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Is it too early to plant tomatoes?

Soil temperature is key to transplant success

Tomato seedlings
Just because they're in the nurseries doesn't mean it's time to plant tomatoes.
These likely were greenhouse-grown, meaning they really need ideal (warm)
soil conditions to get growing. (Photo: Kathy Morrison)

“Can I plant tomatoes now?”

Record warm days have prompted that thought among many Sacramento-area gardeners. Super Bowl Sunday proved to be the hottest February day ever recorded in Sacramento – 78 degrees.

Following several springlike days in the 70s, plants (and people) are responding to this warmth as if it’s April, not mid February. Spring flowers are quickly coming into bloom. Some local nurseries have already started putting out tomato seedlings for sale.

But that doesn’t mean it’s time to transplant those baby tomato plants outside – into the cold, hard ground. Because that soil is still mighty chilly.

According to the UC Davis weather and climate report, soil temperature was still only 51 degrees at its campus weather station Sunday. That’s typical for late winter/early spring. Afternoon air may be warm, but overnight temperatures are still dipping down into the 40s.

Tomatoes need warm soil to grow, develop strong roots and thrive. Transplant a tomato seedling into cold soil, it will just sit there and sulk (or worse).

Ideally, tomatoes and other summer crops such as peppers, squash and eggplant need soil temperatures above 60 degrees before transplanting. Tomatoes prefer soil temperatures even warmer. Oregon State University researchers found that soil temperatures in the 65- to 70-degree range were the sweet spot for tomato transplanting.

When will we see soil temperatures that warm? Most likely April, say the weather forecasters. April also is Sacramento’s traditional tomato transplanting time.

The best way to know for sure in your own garden is to use a soil thermometer. Available at nurseries, this simple device can check soil temperature at a glance; just stick it in the ground. (It’s a lot like checking the temperature of a roast in the oven with a meat thermometer.)

Soil in raised beds warms faster than soil in level ground. The same goes for soil that gets reflected heat from concrete walks or buildings. Wherever, our soil is still not going to reach 60 degrees for at least four to six weeks, say soil experts.

A lot of weather can happen between now and April. Sacramento’s historical frost date – the last day with a threat of freezing overnight temperatures – is March 23. Baby tomato plants also don’t cope well with heavy rain. A March miracle with 3 or more inches of rain would definitely help our water outlook, but could cause any early transplants to damp off in cool, wet soil.

So, wait on the tomatoes for now, and concentrate on leafy greens instead. Your salad garden may not have extra-early Early Girls, but there’s still time to plant more lettuce.

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Dig In: Garden checklist for week of Jan. 29

Bundle up and get work done!

* Prune, prune, prune. Now is the time to cut back most deciduous trees and shrubs. The exceptions are spring-flowering shrubs such as lilacs.

* Now is the time to prune fruit trees, except apricot and cherry trees. Clean up leaves and debris around the trees to prevent the spread of disease.

* Prune roses, even if they’re still trying to bloom or sprouting new growth. Strip off any remaining leaves, so the bush will be able to put out new growth in early spring.

* Prune Christmas camellias (Camellia sasanqua), the early-flowering varieties, after their bloom. They don’t need much, but selective pruning can promote bushiness, upright growth and more bloom next winter. Feed with an acid-type fertilizer. But don’t feed your Japonica camellias until after they finish blooming next month. Feeding while camellias are in bloom may cause them to drop unopened buds.

* Clean up leaves and debris around your newly pruned roses and shrubs. Put down fresh mulch or bark to keep roots cozy.

* Apply horticultural oil to fruit trees to control scale, mites and aphids. Oils need 24 hours of dry weather after application to be effective.

* This is also the time to spray a copper-based oil to peach and nectarine trees to fight leaf curl. Avoid spraying on windy days.

* Divide daylilies, Shasta daisies and other perennials.

* Cut back and divide chrysanthemums.

* Plant bare-root roses, trees and shrubs.

* Transplant pansies, violas, calendulas, English daisies, snapdragons and fairy primroses.

* In the vegetable garden, plant fava beans, head lettuce, mustard, onion sets, radicchio and radishes.

* Plant bare-root asparagus and root divisions of rhubarb.

* In the bulb department, plant callas, anemones, ranunculus and gladiolus for bloom from late spring into summer.

* Plant blooming azaleas, camellias and rhododendrons. If you’re shopping for these beautiful landscape plants, you can now find them in full flower at local nurseries.

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