Always read and follow label instructions!
For the products we sell, mix together in each gallon of spray:
2 oz LiquiCop (= 4 Tbsp)
2.5 – 3.5 oz spray oil
(= 5 – 7 Tbsp, or 1/8 to <1/4 cup)
You can use a hose-end sprayer** if you use the lower amount of oil (you will barely add any water to the concentrated mixture). Otherwise, use a tank sprayer.
Spray the tree thoroughly, to the point of runoff.
It will probably take about two gallons of spray to cover a medium-size tree with conventional training and pruning; one gallon of spray to cover a summer-pruned backyard orchard tree.
Spray peaches and nectarines while they are still dormant.
You can spray other fruit trees such as apricots. plums, and cherries with the same mixture.
Many fruit species such as figs, persimmons, and pomegranates need no spraying. Citrus are sprayed only as needed for specific pest and disease problems.
Dormant and bloom sprays don’t control the worms that get into apples and pears, or the new fruit-fly larvae that are attacking cherries. For those we use growing-season sprays.
The diseases we are concerned about are:
• peach leaf curl, which only affects peaches and nectarines. Sprays are only effective before the buds break. If they show color (green or pink) it is too late.
• brown rot, which primarily affects apricot (and almond) blossoms. See note*. Sprays are only effective when the trees are in bud and bloom. Plums and cherries, as well as peaches and nectarines, can also get brown rot, but it is much less common.
• This spray mixture also helps control shothole fungus, and the oil helps to reduce over-wintering insects.
Notes:
MicroCop (copper sulfate) and Polysul (lime sulfur) are no longer available, so we are now recommending the liquid copper spray. It is less effective for leaf curl, unfortunately, but easier to apply. The problem is that the final spray solution, following label rates, is lower concentration than you were applying before. We cannot recommend that you exceed the label rates.
** You cannot apply both products at the same time in a Dial-A-Pro hose-end sprayer. Apply each at the label rate, 24 hours apart.
* Copper is not effective for brown rot on apricots, and there is no organic or low-toxicity alternative available to homeowners. Chlorothalonil is available, but is very toxic; read and follow label instructions carefully if you choose to use it. Note non-chemical suggestions for control measures at ipm.ucdavis.edu:
Prompt removal and destruction of fruit mummies and diseased plant parts prevents the buildup of brown rot inoculum and helps keep rot below damaging levels. Prune trees to allow good ventilation. Furrow irrigate or use low-angle sprinklers to avoid wetting blossoms, foliage, and fruit. Plant varieties that are least susceptible.
Product information:
LiquiCop
Spray Oil
draft Jan 14 2011
Saturday, January 15, 2011
Tuesday, January 11, 2011
Read and follow label instructions!
Read and follow label instructions.
This is an important phrase! It affects the safety and effectiveness of the products you use. Failure to read and follow label instructions can injure or kill you or others, lead to plant burn, harm beneficial insects and wildlife.
What exactly does it mean? How do we intepret the labels on pesticides?
Signal Word.
Any pesticide, organic or otherwise, is labeled with one of the following words:
Caution
Warning
Danger
Those are in increasing levels of toxicity: Caution products are the lowest toxicity, Danger are the highest. The toxicity is based on direct harm the pesticide may cause by swallowing it, inhaling it, getting it on your skin, or getting it in your eyes. Tests are done to determine how lethal it is and how likely to cause skin or eye irritation.
Different products with the same active ingredient may have different Signal Words due to differing dilution rates of the concentrated or mixed solutions.
Precautionary Statements
These give you a guide as to what makes a particular pesticide dangerous to you or others. It may be swallowing or inhaling the pesticide, absorbing it through the skin or eyes, or direct irritation from contact with the concentrate or mixed spray.
Personal Protective Equipment (PPE):
The label will tell you which protective clothing or gear to wear, how long you, children and pets need to stay out of the treated area. Most people fail to heed this, but it is key to protecting yourself and others from harm.
Environmental Hazards
The label will state whether it is toxic to wildlife. Unfortunately, the impact on bees is not always mentioned. The likelihood of drift, runoff, leaching, and groundwater contamination may be mentioned. These are technical terms that you should understand before you apply the product.
Active ingredient
You may not recognize the name, because a chemical may be better known by its trade name. Example: Daconil is the trade name of chlorothalonil. Manufacturers do not have to disclose the inert ingredients, but do have to list their percentage.
California’s Prop 61 requirement:
If an ingredient in the product, active or otherwise, is “known to the state of California to cause cancer” that must be on the label. It's up to you as to whether that matters to you.
Storage and Disposal
There are general instructions for how to dispose of partially used or empty pesticide containers. Where do you keep your pesticides?
What if you lost the label?
Nearly every company now puts pdf copies of their product labels online. Hey, you can increase the font size and actually read it!
Do organic pest control products have the same labeling?
Yes. Anything that is sold as a pesticide in California has to be labeled. Organic pesticides aren’t necessarily safer than conventional ones.
Here is an example of a commonly used home garden fungicide:
Monterey brand FRUIT TREE, VEGETABLE & ORNAMENTAL FUNGICIDE
“Active ingredient: chlorothalonil 29.6%” You may know this as Daconil, a trade name.
“Known to the State of California to cause cancer.”
Signal Word: “Warning.” Red flag. This is one of the more toxic products homeowners can buy. I always urge purchase and use of a Caution labeled product if possible.
Precautionary Statements: “May be fatal if inhaled. Harmful if swallowed or absorbed through skin. Causes moderate eye irritation. Avoid contact with eyes, skin or clothing. Do not breathe spray mist. Prolonged or frequently repeated skin contact may cause allergic reaction in some individuals.”
Now we know where the Warning label comes from. Given these specific warnings and that higher-toxicity Signal Word, it is important to use the exact protective equipment listed.
PPE: The following are required: long-sleeved shirt, long pants, shoes and socks, protective eyewear, specific types of waterproof gloves, an approved respirator with an organic vapor cartridge or canister with a specific type of filter. You should not even open the bottle until you are wearing all of these listed items.
“Keep children and pets off treated area until dry.” The sprayed material on the leaves can poison them.
Environmental Hazards: Chlorothalonil can kill aquatic invertebrates and wildlife, can drift to nearby water, can runoff into surface water for “several days or weeks after application.” It can leach into groundwater, even when used according to the label.
Directions for Use: These give specific rates of application for certain pests on certain types of plants, by name. The rates are not the same for every crop. Do not exceed them, as they are based on tested effectiveness and are the basis for how toxic the product is considered to be. In some cases they will tell you a maximum amount you can use per year.
The Preharvest Interval (PHI) tells you how many days before harvest you can apply it. These vary by crop (14 days for onions, 7 days for cabbage, day of harvest for carrots), so you need to check the label carefully.
“Avoid spraying plants during extremely hot and sunny weather.” This is because chlorothalonil, like many pesticides, can burn the foliage during hot weather. “Do not apply … within one week … of oil or an oil-based pesticide.” Same issue: you may burn the leaves when used in combination with oil.
Storage and Disposal: These don’t vary much from one product to another, but it is wise to read them. In particular, disposal of the empty container has specific requirements. When you use the last of the bottle, rinse it three times and pour the rinse water into the spray tank. Then puncture the bottle (to prevent re-use) and dispose of it according to local regulations. If you don’t know what those are, contact your local agricultural commissioner.
For some discussion of a new product for vegetables and fruit trees, here is a previous blog article:
http://redwoodbarn.blogspot.com/2010/05/bayer-advanced-fruit-citrus-vegetable.html
This is an important phrase! It affects the safety and effectiveness of the products you use. Failure to read and follow label instructions can injure or kill you or others, lead to plant burn, harm beneficial insects and wildlife.
What exactly does it mean? How do we intepret the labels on pesticides?
Signal Word.
Any pesticide, organic or otherwise, is labeled with one of the following words:
Caution
Warning
Danger
Those are in increasing levels of toxicity: Caution products are the lowest toxicity, Danger are the highest. The toxicity is based on direct harm the pesticide may cause by swallowing it, inhaling it, getting it on your skin, or getting it in your eyes. Tests are done to determine how lethal it is and how likely to cause skin or eye irritation.
Different products with the same active ingredient may have different Signal Words due to differing dilution rates of the concentrated or mixed solutions.
Precautionary Statements
These give you a guide as to what makes a particular pesticide dangerous to you or others. It may be swallowing or inhaling the pesticide, absorbing it through the skin or eyes, or direct irritation from contact with the concentrate or mixed spray.
Personal Protective Equipment (PPE):
The label will tell you which protective clothing or gear to wear, how long you, children and pets need to stay out of the treated area. Most people fail to heed this, but it is key to protecting yourself and others from harm.
Environmental Hazards
The label will state whether it is toxic to wildlife. Unfortunately, the impact on bees is not always mentioned. The likelihood of drift, runoff, leaching, and groundwater contamination may be mentioned. These are technical terms that you should understand before you apply the product.
Active ingredient
You may not recognize the name, because a chemical may be better known by its trade name. Example: Daconil is the trade name of chlorothalonil. Manufacturers do not have to disclose the inert ingredients, but do have to list their percentage.
California’s Prop 61 requirement:
If an ingredient in the product, active or otherwise, is “known to the state of California to cause cancer” that must be on the label. It's up to you as to whether that matters to you.
Storage and Disposal
There are general instructions for how to dispose of partially used or empty pesticide containers. Where do you keep your pesticides?
What if you lost the label?
Nearly every company now puts pdf copies of their product labels online. Hey, you can increase the font size and actually read it!
Do organic pest control products have the same labeling?
Yes. Anything that is sold as a pesticide in California has to be labeled. Organic pesticides aren’t necessarily safer than conventional ones.
Here is an example of a commonly used home garden fungicide:
Monterey brand FRUIT TREE, VEGETABLE & ORNAMENTAL FUNGICIDE
“Active ingredient: chlorothalonil 29.6%” You may know this as Daconil, a trade name.
“Known to the State of California to cause cancer.”
Signal Word: “Warning.” Red flag. This is one of the more toxic products homeowners can buy. I always urge purchase and use of a Caution labeled product if possible.
Precautionary Statements: “May be fatal if inhaled. Harmful if swallowed or absorbed through skin. Causes moderate eye irritation. Avoid contact with eyes, skin or clothing. Do not breathe spray mist. Prolonged or frequently repeated skin contact may cause allergic reaction in some individuals.”
Now we know where the Warning label comes from. Given these specific warnings and that higher-toxicity Signal Word, it is important to use the exact protective equipment listed.
PPE: The following are required: long-sleeved shirt, long pants, shoes and socks, protective eyewear, specific types of waterproof gloves, an approved respirator with an organic vapor cartridge or canister with a specific type of filter. You should not even open the bottle until you are wearing all of these listed items.
“Keep children and pets off treated area until dry.” The sprayed material on the leaves can poison them.
Environmental Hazards: Chlorothalonil can kill aquatic invertebrates and wildlife, can drift to nearby water, can runoff into surface water for “several days or weeks after application.” It can leach into groundwater, even when used according to the label.
Directions for Use: These give specific rates of application for certain pests on certain types of plants, by name. The rates are not the same for every crop. Do not exceed them, as they are based on tested effectiveness and are the basis for how toxic the product is considered to be. In some cases they will tell you a maximum amount you can use per year.
The Preharvest Interval (PHI) tells you how many days before harvest you can apply it. These vary by crop (14 days for onions, 7 days for cabbage, day of harvest for carrots), so you need to check the label carefully.
“Avoid spraying plants during extremely hot and sunny weather.” This is because chlorothalonil, like many pesticides, can burn the foliage during hot weather. “Do not apply … within one week … of oil or an oil-based pesticide.” Same issue: you may burn the leaves when used in combination with oil.
Storage and Disposal: These don’t vary much from one product to another, but it is wise to read them. In particular, disposal of the empty container has specific requirements. When you use the last of the bottle, rinse it three times and pour the rinse water into the spray tank. Then puncture the bottle (to prevent re-use) and dispose of it according to local regulations. If you don’t know what those are, contact your local agricultural commissioner.
For some discussion of a new product for vegetables and fruit trees, here is a previous blog article:
http://redwoodbarn.blogspot.com/2010/05/bayer-advanced-fruit-citrus-vegetable.html
Wednesday, January 5, 2011
In Memoriam: Dan Pratt
I am sorry to report that Sacramento-area nurseryman and garden media personality Dan Pratt died December 25 at the age of 78. Pratt succumbed to injuries from a fall, after a series of illnesses over the last several months.
Employed by Capital Nursery for 24 years, he was heard locally on KFBK (originally KGNR) radio with his Garden Doctor program, which ran for 19 years: first from 9 to 11 a.m. on Saturdays, and then from 8 to 10 on Sunday mornings. For more than 20 years he wrote a weekly column about garden pests for the Sacramento Bee (What’s Bugging You?) and made frequent appearances on local television. His annual garden calendar was sold at garden centers throughout Northern California.
Pratt gave many talks over the years to garden clubs around the Sacramento Valley. He was active in the local chapter of the California Association of Nurseries and Garden Centers, serving as president twice and on the board of directors for several years. Dan led garden tours of Britain and other regions. After his retirement he moved back to his family’s property in Napa.
He leaves a son and daughter and longtime girlfriend. A private burial service has been held.
That all sounds very dry. I considered Dan a friend for over 25 years, having met him when I first got involved in our local chapter of the nursery association. He was always full of ideas, present at nearly every nursery event we worked on, and enthusiastically promoted gardening and the nursery industry. Dan introduced me to radio work and graciously allowed me to host his show when he traveled. After retirement, he and Jo stopped by my shop any time they were passing by Davis, to swap stories and tell jokes. He liked good food, cruises, and terrible puns.
Dan Pratt was a great friend of gardens, gardeners, and garden centers everywhere.
Addendum: from the Sacramento Bee Jan 7 2011
Employed by Capital Nursery for 24 years, he was heard locally on KFBK (originally KGNR) radio with his Garden Doctor program, which ran for 19 years: first from 9 to 11 a.m. on Saturdays, and then from 8 to 10 on Sunday mornings. For more than 20 years he wrote a weekly column about garden pests for the Sacramento Bee (What’s Bugging You?) and made frequent appearances on local television. His annual garden calendar was sold at garden centers throughout Northern California.
Pratt gave many talks over the years to garden clubs around the Sacramento Valley. He was active in the local chapter of the California Association of Nurseries and Garden Centers, serving as president twice and on the board of directors for several years. Dan led garden tours of Britain and other regions. After his retirement he moved back to his family’s property in Napa.
He leaves a son and daughter and longtime girlfriend. A private burial service has been held.
That all sounds very dry. I considered Dan a friend for over 25 years, having met him when I first got involved in our local chapter of the nursery association. He was always full of ideas, present at nearly every nursery event we worked on, and enthusiastically promoted gardening and the nursery industry. Dan introduced me to radio work and graciously allowed me to host his show when he traveled. After retirement, he and Jo stopped by my shop any time they were passing by Davis, to swap stories and tell jokes. He liked good food, cruises, and terrible puns.
Dan Pratt was a great friend of gardens, gardeners, and garden centers everywhere.
Addendum: from the Sacramento Bee Jan 7 2011
Friday, December 24, 2010
Mandarins!
Satsumas and other mandarins
Written for the Davis Enterprise, December 23, 2010
Click on any image for a larger version
We get questions, this one from Davis Enterprise columnist Dan Kennedy:
Please tell me about satsumas and the other types of mandarins: what they are, which are best here, why a frost improves the flavor, and how to grow them.
Dan's recent column [Satsumas, the sweetest citrus, Dec. 8 2010, Davis Enterprise, available to subscribers at their web site] focused on the buying and eating part, and touched on how to grow them. But questions about citrus always seem to beget more questions, as they are a complex group of fruit trees.
Mandarin oranges are a sign of the holiday season in California. In my Southern California childhood it was a Dancy tangerine that filled the toe of the Christmas stocking. We'd spit the seeds at each other out on the dichondra lawn as we waited for the grownups to waken. Dancy is a rich-flavored, juicy, seedy, easy-to-peel type of mandarin orange (tangerine and mandarin are interchangeable terms) that ripens in time to market for the holidays.
What exactly are these Satsuma mandarins we grow?
Satsuma is a generic term for a number of different varieties of (mostly) seedless, easy-to-peel mandarin oranges. The UC Riverside Citrus Variety Collection site lists over a hundred different clonal lines called mandarins, representing a couple of dozen species, numerous hybrids, and many bud sports. Of those, over three dozen from various sources are called Satsumas. Owari Satsuma is the best known, and the classic reference The Citrus Industry (1967) describes Owari as "of ancient and unknown Japanese origin presumably from the old province of Owari, whence the name."
Most common in California is a variant called Frost Owari. H. B. Frost was a researcher at the UC Riverside Citrus Station in the early 1900's. The name has nothing to do with cold-hardiness. (There is also a Frost Lisbon lemon and a Frost Marsh grapefruit, named in honor of Frost's work at developing nucellar seedling clones. That's a whole 'nother column.)
'Owari Satsuma' mandarin
Satsuma, a name we apply to popular mandarin and plum varieties, is just a region of Japan. Be careful what you ask for if you're visiting: they don't call them "satsumas" there, but they do apparently use the term for a type of sweet potato! From a blog: "The area of Satsuma is not famous for tangerines and so it's very strange for us Japanese that Satsuma indicates tangerines in English."
What is a bud sport?
It is a naturally occurring mutation on a branch that differs sufficiently to be noticed and propagated as a separate variety. They occur in many plant, including roses and fruit trees and especially citrus. Bud sports may differ in size, color of the flesh or peel, how early they ripen, variegation of the foliage, etc.. For example, I sometimes get Dobashi Beni Satsuma trees from one grower, "reported to be a limb sport of Owari in the orchard of K. Dobashi in 1940 [in Japan] … Distinctive only because of its deep orange-red color."
What are some other mandarins?
Clementine is another great-selling variety. It ripens later and has somewhat tighter skin. There are several clones of Clementine. In some cases, particularly some earlier-ripening clones, seed is produced when the flower is pollinated. Seeds in a mandarin reduce the market value, so growers want to isolate them from bees to try to keep them seedless. This has led to a dispute between beekeepers and Clementine growers, as the citrus growers want bee-free zones of two miles around their groves!
Cuties® is a marketing device for selling smaller Clementine and Murcott mandarins.
Similar-sounding Pixie is a new variety of mandarin that ripens later and holds up well after harvest, so it extends the mandarin season. There are others: Four Winds Growers in Winters lists 13 different varieties of mandarins for our region.
Why is the fruit sweeter after a frost?
It is the conversion of malic and citric acids to sugars that makes the fruit palatable, and this tends to occur with cold temperatures. Conversion of acids and starches to sugar creates a natural anti-freeze in fruit, leaves (kale leaves are sweeter after frost), stems (maple syrup!), and roots. Preferably not hard freezing temperatures for citrus, as that causes breakdown of the flesh into undesirable off-flavored components and releases bitter compounds from the membrane.
A freeze can do considerable damage to the crop from damage to the trees, but also by making the fruit unusable even for juice. If the growers move fast, they can harvest and process the fruit quickly before off-flavors develop. When a regional freeze threatens, you may see workers harvesting citrus in the middle of the night!
Which ones can we grow?
All mandarins grow readily here, and varieties can be selected for early or later ripening. For example, Owari + Clementine + Encore + Pixie provides fruit from November nearly into summer. The small trees can be planted quite close together to maximize fruit production in a small yard.
Mandarins are among the cold-hardiest citrus. Four Winds Growers recommends frost-protection at 28 degrees, but my Owari trees and fruit have tolerated temperatures into the low 20s without damage. Gold Nugget and Yosemite are new patented varieties that are even more tolerant of cold.
Growing tips!
These small, slow-growing plants can be trained as shrubs or small trees, and can be kept in large containers for many years.
As with all citrus:
- -- plant in a warm, sunny location: as they say at Four Winds Growers, "where the cat sleeps in the sun, citrus grows well;"
-- dig a wide hole, loosening the soil but not amending it;
-- plant "crowned up" -- i.e., with the tree set on a slight rise;
-- make a watering basin around the tree so you can soak it thoroughly and infrequently;
-- fertilize regularly: monthly (or at least seasonally). Adjust pH with soil sulphur, and correct micro-nutrient deficiencies as needed.
Expect fruit beginning in 3 - 4 years, with yields increasing each year thereafter.
More questions:
How long are they ripe, and how can you tell?
The skin loosens over time but is not a reliable indicator of sweetness. It does tell you that the fruit will soon be past its prime. Color of the peel is not a reliable indicator, either. Go by the calendar and sample the fruit, starting in late November. Satsuma mandarins have a narrow ripening range. Around here they are edible by Thanksgiving, though tart; great for the holidays and into January, and then they spoil quickly after rainy periods in January. By February they are puffy and poor quality. Rain is a big factor: the thin peel of satsumas is easily bruised (compared to, say, a navel orange) and rots quickly, damaging the fruit.
Why is the Owari Satsuma mandarin so popular? It's easy to peel and break into segments, seedless, sweet and juicy, and early ripening. Satsumas ripen November through January, marking the start of the citrus season. And it is one of the hardiest citrus for our area. Other mandarin varieties ripen January through spring, with some new types holding on the tree into the early summer.
Visit Redwood Barn Nursery's Home Page |
Tuesday, December 14, 2010
How many chilling hours do we get?
We get lots of questions about "chilling hours" -- the number of hours between 32F and 45F that deciduous fruit trees need in order to break dormancy and flower properly. You will often see the number of hours that a particular variety needs printed right on the label; e.g., Elberta Peach 800 hours. Gardeners in the Bay Area and Southern California may not get sufficient chilling for many varieties, and need to inquire locally about which are recommended for their area.
I've attached an image showing the 15-year trend in chilling for Davis, Ca. Note that the first year shown (1995-96) was unusually low. Chilling hours in the Davis area typically range from 800 - 1000, allowing us to grow nearly any fruit variety available.
For the chilling hours in your area, check this website which shows weather stations all over California:
http://fruitsandnuts.ucdavis.edu/chillcalc/index1.htm
Wednesday, November 24, 2010
Frost Warning? Freeze Warning?
Written for the Davis Enterprise, November 24, 2010
Click on any image for a larger version"He comes, - he comes, - the Frost Spirit comes!
On the rushing Northern blast ... " John Greenleaf Whittier
This week marked the first National Weather Service frost warning of the season. Our main frost season typically runs from Thanksgiving through Valentine's Day. There have been frosts after Feb. 14, and occasionally before the last week of November, but those have been infrequent and of little consequence.
What weather conditions lead to a frost warning?
The poem was a bit of hyperbole on Whittier's part: frost doesn't "rush" in, it forms under still, clear skies. But he had a point. Frost can occur after a cold air mass, usually a storm, moves through the region. Cloud cover during the day gives way to clear skies in the early evening. As heat is lost to the sky, the surfaces cool rapidly. When the air temperature gets to the dew point, fog forms. When surface temperatures drop below freezing, frost forms. [Note that the air temperature you measure or see online may still be above freezing; it is the surface temperature that matters.]
When the surface reaches 32 degrees, the layer of water vapor molecules in contact with that surface freezes, and then the layer above that, and so on. Frost doesn't fall from the air, it freezes directly on a surface. Some surfaces cool faster than others. The metal on your car may show frost by midnight; bare soil by dawn, while grass might not even reach freezing that same morning. It all has to do with how efficiently the particular surface conducts heat.
What would prevent the frost?
"The Frost performs its secret ministry,
Unhelped by any wind." - Coleridge
Unhelped by any wind." - Coleridge
Clouds and fog prevent frost by trapping the outbound heat. Light winds mix the warmer air from above back down to ground level. This is the principle behind the giant fans you see on the edges of vineyards in Napa Valley.
What's the potential for harm in the garden?
Leaves lose heat to the sky! Damage to a plant depends on the structure and contents of those leaves. Soft, succulent plants such as Impatiens turn to mush as the cells rupture. Hardy plants contain sugars and other chemicals that act as natural antifreeze.
A frost is not a freeze.
First, don't panic. If a plant is considered hardy here, damage will be cosmetic. The leaves may look ugly, but the plant will survive. It is a freeze that we are concerned about: a period of colder temperatures when a very cold air mass moves over the region.
Our biggest risk is mid-December to mid-January. Temperatures below the mid-20's are unusual here and spell trouble for many plants. On December 23 1990 we reached 16 degrees. The morning of January 14 2007 got to 20 degrees.
Freeze damage is a matter of how cold we get, for how long. That morning in 1990 was the start of a ten-day episode, with each successive day causing further tissue damage to leaves, shoots, and eventually the woody parts of plants.
Which plants are we going to lose on a frosty night?
Pansy 'Delta Premium' -- no need for protection!
Which plants should we protect from frost?
Some succulents such as jade plant, some aloes, and kalanchoes.
Tender subtropicals such as hibiscus and mandevilla.
Semi-tender subtropicals such as bougainvillea, Guatemalan avocado, Mexican lime, young lemon and citron trees.
Which plants should we protect from a freeze?
Older lemons, other young citrus trees, Mexican avocado, geranium (Pelargonium). Blossoms of Lilac vine (Hardenbergia), which bloom in late winter, can be saved by covering the plants.
As temperatures drop further we may get concerned about some of the hardier citrus. Tangeloes, grapefruit, navel and Valencia oranges can be damaged in the mid-20's.
There are many subtropical plants I don't worry about. Brugmansia, lantana, and passionflower may defoliate, or be partially killed, but will recover. Once you get used to the winter appearance of these semi-tender plants, you'll worry less. Just think of them as deciduous. Leave them alone: wait until new growth begins in spring before you cut off the frost-burnt parts.
Passiflora 'Coral Glow'
We grow many subtropical plants in Northern California. Some are badly harmed by freezing weather, while others (such as the Coral Glow Passionflower shown here) re-sprout readily in spring. Temperatures in the upper 20's will damage the leaves and cause some die-back, but the plants will recover. Lower temperatures may completely kill the tops. Damage can be reduced by taking simple measures to trap or provide heat to the plant.
Some citrus are much hardier than lemons and limes. My mandarins and kumquats have been through major freezes with minimal damage. Fruit of Satsuma mandarins may be harmed at very low temperatures, so you might harvest the fruit if extreme cold is predicted. But citrus fruit won't ever get any sweeter once you pick it, so stripping the tree is a last resort.
There are two main ways to protect plants:
Trap heat.
A plant under an overhang is safe, as the building will keep the heat from escaping to the sky. Frost blankets, which are made of light fabric that allows light in, act to create a mini-greenhouse. Anchored with metal pins, these are the simplest way to provide protection.
Using frost blanket to protect fruit on a mature lemon tree.
Provide heat.
Old-fashioned holiday lights generate enough heat to keep the plant warm. Even a 40-watt bulb on a shop light fixture, attached at the base of the tree (grounded outdoor-rated only!) may be enough for a small tree. Combined with the frost blankets, you can get a few degrees of warmth, enough to keep the local temperature above freezing.
Finally, plants in containers may be damaged by desiccation (cold-induced drying) during freezing weather. Keep your outdoor containers watered during the winter! They won't need it very often: once every week to ten days should be fine if we don't have rain.
Monday, November 8, 2010
Fall Color in the Sacramento Valley!
Why do leaves turn color in the fall?
This is right up there with 'how do they grow seedless watermelons?' among the most-asked questions directed at plant professionals.
The answer is simple! The days get shorter, the nights get colder, and Jack Frost magically paints the leaves in your yard!
Well, actually, the answer is more complicated, involving daylength (actually nightlength), temperature, nutrients, and genetics.
Trees that have adapted to cold winter climates go through several steps as winter approaches. The first part of the process is a reaction to longer nights. The plant forms a layer at the base of the leaves that blocks the movement of carbohydrates (sugars, starches) out of the leaves, and blocks the movement of minerals into the leaves. That 'abscission' layer eventually gets brittle and breaks, so the leaf falls.
October Glory maple
But before that happens, the plant produces less and less chlorophyll because it has less stuff to make it from. That is the pigment which makes leaves green. It is also the most fragile pigment, breaking down in sunlight very quickly. Usually the plant is replenishing it very quickly. But as it breaks down and becomes less abundant, the less common pigments of yellow and orange become visible. So these are the first fall colors that we see. Those colors were already there; we're just seeing them now because the green is gone. This first reaction mostly follows the calendar, although severely drought-stressed plants will begin to go dormant earlier than normal.
Some minerals are mobile within the plant, moving from one place to another as needed. The plant moves phosphorus out of the leaf and into the stem where it is stored during cold weather. The absence of phosphorus changes the chemical reaction in the leaves, and the remaining trapped carbohydrates are now made into certain other pigments, notably the ones that are red and purple. So these are the more spectacular colors that we see next. They weren't there before; the tree is making them now out of what's left in the leaf.
Chinese pistache leaves
Some trees make more of these pigments than others do, so it varies between species. There are also genetic differences of seedlings within a species. Variation in temperature from year to year, and the nutrient status of the specimen, also affects fall color. Within those species that have the pigments to begin with, sunny clear days and cool nights encourage the production of more red and purple pigments. A tree with adequate nutrition will have more basic material to work with to create pigment. Trees that are overwatered have damaged root hairs, so they've been unable to take up nutrients readily during the summer.
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