Monday, February 4, 2013

Lilacs and Redbuds for Spring!

Lilacs and Redbuds for the Sacramento Valley

Watch out for sentences that begin with “in my day.” It's a sign that some old guy is about to tell you a story about the way things used to be.

Syringa 'Sensation' -- lilac

Well, in my day, people planted fruit trees in the winter, bulbs in the fall, tomatoes in April or May. And some flowering shrubs (including roses) and shade trees were also planted in the winter, when they're dormant. But as each new cohort of beginning gardeners comes along, I realize that these seasonal gardening cycles haven't been passed down from the previous generations. Nowadays lots of people look for daffodils in spring, fruit trees in summer. Industry terms like “bare-root” are no longer common knowledge.

Most deciduous fruit trees, most roses, many shade trees, and a lot of flowering trees, shrubs, and vines are grown in fields like agricultural crops. They're planted very close together, pruned and trained minimally, and then dug up by machines in December. That's when the whole supply for the season becomes available. All the soil is washed off the roots, and they are stacked and bundled and shipped off to nurseries all over the world.

The roots are bare, so they are called bare-root. They're dormant, and stay that way for several weeks. So garden centers can stick them in shavings or sand, keep them moist, and (hopefully) sell them to you before they leaf out. Or they can pot them up when they have time. If sales are strong, selection tends to dwindle by late spring. This applies to certain popular flowering shrubs. I want to highlight two of these that have best availability in the winter and spring.


“I didn't know we could grow those here!” is the most common thing I hear about this old favorite garden plant. This is reinforced by many online resources which inexplicably list lilacs for “zones 3 through 7.” We're in USDA zone 9. They don't bloom reliably in Southern California or coastal climates due to a lack of winter chilling. But we get sufficient chilling here, and they sure do bloom.

Those online references are usually from the East coast or Midwest, and California is different. The zones they are referring to are USDA zones. West-coast gardeners do better to use the Sunset Western Garden Book. We're Sunset Zone 14, and Sunset lists the Common lilac (Syringa vulgaris) for zones 1 - 11 and 14.

When we bought our rural property it came with lilacs that had been planted decades prior by the original owner. They've always grown and bloomed well for us with very little care; in fact, the original shrubs have reseeded. And I've planted more. Lilacs tolerate nearly any soil type, prefer alkalinity (something that likes Davis water!), and accept drought. Full sun is best. They will grow in some shade, but mildew on the leaves can be a problem. You can prune them, or not, as you prefer. Just wait to do it until after they bloom. The only caveat as to location is that they should not be in a cold-sheltered location. Lilacs want winter chill, so don't plant them against your house. Out in the open is best.

Cercis 'Don Egolf' -- Chinese redbud
There are hundreds of varieties; dozens of species, with many hybrids within and between those species. Best-known and loved are the varieties of Common lilac (Syringa vulgaris), as they have the largest flowers and most fragrance. They bloom at the end of the branch in the spring, and the bushes have an upright habit. Others bloom all along the branches, with clusters of smaller flowers, often also very fragrant. A good example is the Arboretum AllStar, the laceleaf Persian lilac (Syringa x persica laciniata). These tend to have a more informal, arching growth habit.

Climate change indicators?

My lilacs bloom from early to late April, varying slightly by year and by variety. Lilacs have long been noted as plants that mark the season: their leaf emergence and bloom is a sure sign of spring. In fact, they hold a special place in the study of phenology, which is the science that connects seasonal biological phenomena to variations in climate. Gardeners and botanical gardens have been recording the dates of flowering of lilacs for generations.

Phenology is just a fancy term for what old gardeners have done for years. “Plant corn when oak leaves are the size of a squirrel's ear,” is an example. Handy if you have an oak tree and a squirrel nearby. Or this: “Plant bean, cucumber, and squash seeds when lilac is in full bloom.”

In the 1950's a more systematic approach to using phenology was developed. In order to provide consistency, and avoid planting an invasive species, a naturally sterile variety of Syringa chinensis called Red Rothomagensis was distributed to hundreds of sites around the country, and a reporting network was created. The results? “Regional differences were detected, as well as an average 5-6 day advance toward earlier springs, over a 35-year period from 1959-1993… spring warming is strongest regionally in the northwest and northeast…” So when grampa says, “sure seems like the lilacs are bloomin' earlier than they used to,” he is right.

Want to participate? Check out the USA National Phenology Network at

Red Rothomagensis is sometimes available in garden centers.


Every March when the redbuds in the Arboretum come into bloom, we get lots of inquiries. Compared to lilacs, these get a little dicier. Do they grow here? The answer is more complicated.

Western redbud (Cercis occidentalis) is our native species, represented locally in the Warren G. Roberts Redbud Collection in the UC Davis Arboretum. It grows fine here so long as you don't water it very often after it is established (usually by the second summer). Western redbud is very prone to crown rot if it gets watered too frequently. It is a multi-stemmed shrub, rarely grown as a tree.

Eastern redbud (Cercis canadensis), very common in nurseries, doesn't like our dry heat. During hot spells the leaves get badly spotted and burnt. That goes for the regular species as well as the red-leaved variety called Forest Pansy. You can try planting them in the shade of a taller tree, but expect unsightly foliage by mid-summer. This species is not at all drought tolerant.

Just to confuse things, a variant or hybrid of the Eastern redbud called the Oklahoma redbud is quite heat tolerant. Usually classed as Cercis canadensis texensis, it has a thicker, glossier leaf that resists sun scorch. A smaller tree than the Eastern redbud, but larger than our Western redbud, it can tolerate some drought, and also can take regular watering, so it is one of our best choices for the garden.

Yet another good garden variety is a variety of Chinese redbud (Cercis chinensis) called Don Egolf. This seedling was discovered in the U.S. Arboretum in Washington. Very slow-growing, it also happens to be naturally sterile. If the seed pods of the other types bother you, this one is cleaner. The flowers are a more intense dark magenta purple than the other varieties. Tolerant of watering as well as some drought, it has an upright form but only appears to get to about ten feet tall.

Redbuds can tolerate nearly any soil type, and don't mind alkaline water. No pruning needed.

Lilacs and redbuds both fit in a low-water landscape. They have spectacular blooms, and are carefree.