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Winter chill brings out spring lilacs

Even low-chill varieties need some cold time

Lilacs are putting on a show right now, thanks to enough winter chill hours. (Photos: Debbie Arrington)





More proof we had a chilly (if dry) winter: Lilacs.

Throughout my Sacramento neighborhood, lilacs are putting on a spectacular spring show. That includes my own backyard.

Of course, these are “low-chill” varieties such as Lavender Lady, California Rose and Angel White. They still need a considerable amount of “chill hours” (often 500-plus), but nowhere near that of higher chill varieties. Chill hours measure the time spent below 45 degrees.

Lilac blooms
Unfortunately the perfume of these lilacs can't be shared in print.

Bred to be grown in USDA Zones 3-8, most hybrid lilacs require 2,000 chill hours. That’s more than double what we typically get in Sacramento (USDA Zone 9). Our final totals for the winter of 2020-2021: 730 to 1,012 chill hours in the Sacramento Valley and 859 to 1,195 chill hours in the foothills.

But that was enough to prompt those local “low-chill” lilacs to bloom like crazy.

Now is a good time to shop for lilacs in nurseries or admire them in landscapes. This when they look (and smell) their best.

Even with plenty of chill, common lilacs ( Syringa vulgaris ) and their hybrids can be tricky to get to bloom year after year. Like hydrangeas, their flowers are dependent on well-timed (or no) pruning.

Next spring’s flowers form on the stems right after this year’s blooms are done. But you’ve got to do something; leaving the spent flowers on the bush can inhibit blooming the next year, too.

The trick is to snip off the spent blooms where the leaves join the stem just above where the new buds are forming. Don’t prune heavily and never after Memorial Day; if you do, you won’t have flowers the next spring.

Lilacs don’t need much fertilizer. Give them a little bone meal while they’re dormant in winter. They need at least six hours a day of sun and good air circulation. (When crowded, they can develop powdery mildew.) In Sacramento, they prefer morning sun and some afternoon shade; otherwise, they can get sunburned.

Bee on a lilac blossom
Bees enjoy lilacs, too.
Lilacs demand good drainage and soil on the slightly acidic side. Water-wise, they like deep irrigation once a week or twice a month, depending on the heat. They don’t like life next to a lawn; that’s when they tend to get over-watered. Constant year-round irrigation also keeps lilacs from entering dormancy; they need that winter sleep to develop their blooms.

Butterflies and beneficial insects love lilacs. Expect to see swallowtails enjoying this spring bloom.

Lilacs also require patience. After transplanting, a new bush may not bloom for three years – or more. But once established and comfortably chilly, it will start flowering relatively reliably for decades to come.

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Garden Checklist for week of Feb. 16

Take advantage of this nice weather. There’s plenty to do as your garden starts to switch into high gear for spring growth.

* This is the last chance to spray fruit trees before their buds open. Treat peach and nectarine trees with copper-based fungicide. Spray apricot trees at bud swell to prevent brown rot. Apply horticultural oil to control scale, mites and aphids on fruit trees.

* Check soil moisture before resuming irrigation. Most likely, your soil is still pretty damp.

* Feed spring-blooming shrubs and fall-planted perennials with slow-release fertilizer. Feed mature trees and shrubs after spring growth starts.

* Transplant or direct-seed several flowers, including snapdragon, candytuft, lilies, astilbe, larkspur, Shasta and painted daisies, stocks, bleeding heart and coral bells.

* In the vegetable garden, plant Jerusalem artichoke tubers, and strawberry and rhubarb roots.

* Transplant cabbage and its close cousins – broccoli, kale and cauliflower – as well as lettuce (both loose leaf and head).

* Indoors, start peppers, tomatoes and eggplant from seed.

* Plant artichokes, asparagus and horseradish from root divisions.

* Plant potatoes from tubers and onions from sets (small bulbs). The onions will sprout quickly and can be used as green onions in March.

* From seed, plant beets, chard, lettuce, mustard, peas, radishes and turnips.

* Annuals are showing up in nurseries, but wait until the weather warms up a bit before planting. Instead, set out flowering perennials such as columbine and delphinium.

* Plant summer-flowering bulbs including cannas, calla lilies and gladiolus.

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