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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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Dig In: Garden Checklist

For week of Sept. 24:

This week our weather will be just right for fall gardening. What are you waiting for?

* Now is the time to plant for fall. The warm soil will get these veggies off to a fast start.

* Keep harvesting tomatoes, peppers, squash, melons and eggplant. Tomatoes may ripen faster off the vine and sitting on the kitchen counter.

* Compost annuals and vegetable crops that have finished producing.

* Cultivate and add compost to the soil to replenish its nutrients for fall and winter vegetables and flowers.

* Fertilize deciduous fruit trees.

* Plant onions, lettuce, peas, radishes, turnips, beets, carrots, bok choy, spinach and potatoes directly into the vegetable beds.

* Transplant cabbage, broccoli, kale, Brussels sprouts and cauliflower as well as lettuce seedlings.

* Sow seeds of California poppies, clarkia and African daisies.

* Transplant cool-weather annuals such as pansies, violas, fairy primroses, calendulas, stocks and snapdragons.

* Divide and replant bulbs, rhizomes and perennials. That includes bearded iris; if they haven’t bloomed in three years, it’s time to dig them up and divide their rhizomes.

* Dig up and divide daylilies as they complete their bloom cycle.

* Divide and transplant peonies that have become overcrowded. Replant with “eyes” about an inch below the soil surface.

* Late September is ideal for sowing a new lawn or re-seeding bare spots.

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