Saturday, July 7, 2012

Garden Questions in Early Summer!

I heard the “climate zones” have changed because things are getting hotter. Which zone are we in now?
Recently the USDA Plant Hardiness Zones were changed to reflect the warmer winters that have been observed in many parts of the country. No changes were made to California zones, because winter temperatures have not warmed in most parts of our state. The major changes have been observed in the southeastern U.S.
Western gardeners generally use Sunset Zones, not USDA zones. USDA zones only reflect winter low temperatures. Sunset Zones, created by the publishers of the Sunset Western Garden Book years ago, are much more detailed, showing the differences caused by local geography. Davis is in Sunset Zone 14: a hot interior climate with strong coastal influence (the delta breeze that we all appreciate so much on summer evenings). Woodland is in Sunset Zone 8: less coastal influence. For winter hardiness purposes, both are in USDA Zone 9.
So a recent comment in a gardening article in the Sacramento Bee got me curious. From the June 12 edition, in an article titled Gardening's Busy Season Starts With Understanding Climate, an author from the Bay Area is quoted, "Our weather is changing. I've lived in Alameda my whole life, and it's not the same climate I grew up with - it's hotter. We have to adapt. It's one more challenge for gardeners."
Well, the statistics don't actually show that for many parts of California, and particularly not for coastal areas such as Alameda. 30-year temperature data compiled by the National Climate Data Center shows average temperatures have dropped in California's coastal cities and areas such as Davis and Sacramento that have strong coastal influence, while temperatures have increased slightly in interior cities such as Fresno and Redding that don't have the delta breeze. Reasons? Perhaps the Pacific Decadal Oscillation, of which we are in a cool phase.
Bottom line: California gardeners needn't worry about reports of gardening zones changing. Your old books are still valid.

Question from another plant pro: Thrips on roses. What is your experience and what would you recommend to a homeowner to manage the situation? They used the Bayer 3 in 1 product 10 days ago.
Thrips are tiny insects that feed on the tips of the rose buds before they open, causing the petals to distort and the flowers to open imperfectly. Pull back the petals and you will see fast-moving very skinny insects less than a quarter-inch long inside the bloom. Thrips in our area show up on flowers as the nearby grasses dry off in late spring and they move into our gardens looking for food; they are worse on light-colored roses than dark ones.
Spraying with anything is likely to delay the population increase of the natural predators. It isn't the answer the gardener wants, but it's the honest one. We all need to stop selling and using the combination products due to their environmental harm and unintended consequences.
Bayer 3 in 1 is a combination insecticide, miticide, and fungicide. The insecticide part is taken up into the plant and poisons the insect after it feeds. Since it has to feed first, and the feeding is what causes the damage, you still get the damage. It is one of the very worst combinations a gardener can apply with respect to harming bees. Combine tau-fluvalinate with tebucanazole and imidacloprid? Toxicity of the first ingredient to bees increases something like 1000-fold when combined with SBI fungicides such as tebucanazole. And the imidacloprid itself is known to be harmful to bees. So we have a gardener unnecessarily applying a miticide and a fungicide to a plant on which the only identified pest is an insect, and doing significant harm to bees and other beneficial insects with a product that will only marginally manage the thrips (if at all).
Neem sprays might help, since they could smother existing thrips and repel any new ones. Vigorous washing of the plant might help, and will reduce aphids and mites in any case. Ace hardware stores sell a hose-end pressure washer that is great for managing pests on garden plants. More to the point, thrips season will pass. Beneficial insects populations will catch up with the thrips, hot weather will reduce the reproductive rate of the pest, and your roses will be back to normal again.
Bottom line: there is no conventional pesticide, labeled for thrips or not, that gives good control on roses. The damage is done to the blossom before the pesticide takes effect, even if it works. Thrips populations develop resistance to pesticides very quickly. Some products have very adverse effects on beneficial insects. I know garden center professionals want to sell a solution to a problem, but often I find myself explaining that we don't have one. These problems tend to be seasonal and of short duration.

A dwarf Butterfly bush? Wowzer!
We appreciate your enthusiasm. Yes, breeders have achieved short, compact-growing Buddleias. Commonly called Butterfly bush, Buddleias have been long-time garden favorites for their long season of bloom, fragrance, attraction to hummingbirds as well as butterflies, and tolerance of heat and drought. But even the most compact types got to 5 to 6 feet tall, and the older ones were even taller and rangier.
Enter the Buzz Buddleias, and the Flutterbye Petite Buddleias. Little three-foot mounds of color, blooming non-stop from May through summer. Available in purple, lavender, pink, and white, these can be kept in containers or planted in the front of the border. Mix them with lavender, rosemary, rockrose, or other sun-loving low shrubs and perennials.

My clematis came up and bloomed real nicely, and now it's set those seed things. How can I get it to bloom again? Do I have to cut those off?
That plant won't bloom again this season. Each clematis variety blooms for a few weeks. But there are varieties available for bloom at different times spring through mid-summer. The seedheads are interesting and sort of attractive; removing them is tedious, unnecessary, and won't yield any further bloom.
Clematis have a reputation for being fussy. They're not, really; they just like their roots in rich, loose soil that is shaded a bit, and they need regular watering. The tops are fine in full sun or partial shade. Once established, they can be very long-lived and carefree.
Most types put on vigorous growth in just a few weeks in the spring, then bloom, and then rest for the remainder of the season. So the key is to keep the root system healthy and vigorous to build up the plant for the next growing season. Fertilizing in late summer with an organic plant food will help make a more robust plant the following year.

I bought some moss ground cover and planted it in the shade, and it isn't doing well. Looks like it's dying. Is it not getting enough water?
Wrong plant, wrong place. Or if you prefer: misleading common name. Irish moss and Scottish moss (varieties of Sagina subulata) are actually not mosses at all. They are in the carnation family and prefer full sun and slightly dry conditions. For a soft green look in moist shade, try Baby's tears (Helxine soleirolii).

My tree in my lawn has never grown as well as the others. Should I feed it? Why do you recommend keeping grass clear away from trees?
Grass roots compete significantly with tree roots! Trees planted with grass growing up to their trunks grow as much as 30% more slowly than those with the grass cleared. Feeding trees in the lawn is very difficult because grass roots are very efficient at 'stealing' nitrogen. You end up feeding the grass, not the tree. Clear the grass from an area at least 3 to 4 foot diameter around each tree. Then you can fertilize a young tree, using an organic source of nitrogen in spring and/or fall. Established trees need no feeding unless they show specific deficiency symptoms.
Trees in grass are also vulnerable to damage from power equipment such as mowers and especially weed trimmers. Repeated damage harms the water and food conducting part of the tree (the cambium) and stunts it, and creates an avenue for disease to enter. Finally, grass or mulch up against the stem of any plant traps moisture, inviting crown rot fungus. Trees and grass don't mix!

For further reading:
To check out the new hardiness zone map, visit

Want to see the differences from 1990 to 2006? For an interactive map, visit:

Article about climate data:

For more on pesticide interactions:

Dwarf butterfly bush is a great new addition to the dry, sunny flower border. Shown here with Euphorbia Ascot Rainbow is the variety Buzz Purple. These compact shrubs grow to three feet or so with equal spread. Butterfly bushes bloom on new growth, so they can be trimmed or cut back as needed. Hummingbirds and butterflies love them.

Here is the Buzz Buddleia in front of a more typical butterfly bush. The tight growth habit, with smaller leaves, leads to a mound of grey-green leaves and continuous purple flowers from spring through summer. These new dwarf hybrids are sterile, so blooms are more abundant (no energy going into seed production), and they won't reseed.

As of late June, our Clematis Ville de Lyon has been blooming since late May and will continue for another couple of weeks. The flowers are followed by interesting seedheads. Clematis like soil that has been enriched with compost, and the roots prefer shade. But the tops can grow up into full sun, or will bloom adequately in partial shade. Established vines can give dozens of blooms over several weeks, with varieties that start in early spring and others blooming in summer.

Clematis montana hybrids bloom in spring, usually March to April. The blossoms are smaller than later hybrids, but more abundant. The blooms smell lightly of vanilla. The Montana hybrids are unusual in that they bloom on old wood, so they should be pruned only after they have finished flowering. The pink flower shown is C. montana Mayleen, and the white one is C. montana grandiflora.

The Viticella hybrids bloom mid-summer, after most other Clematis are done. This plant, a variety called Polish Spirit, is scrambling all down a Nandina hedge on the north side of my house, and provides dozens of blooms over several weeks. Clematis naturally like to grow behind other plants, climbing up onto shrubs, trees, or climbing roses. They are light and open, so they don't suffocate the plant that is supporting them.

It's called Irish moss, and it looks like moss, but students of botany will recognize that it can't be a true moss: mosses don't flower! It's actually a ground cover in Caryophyllaceae, the carnation family. Irish and Scottish mosses prefer full sun.

For a mossy-looking ground cover for moist shade, try Baby's tears. It looks delicate, but can actually spread pretty freely in the shade. Baby's tears won't tolerate direct sun, and may frost back a bit in winter (but aways recovers). Great around stepping stones or with ferns and woodland flowers.

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