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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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Garden Checklist for week of June 8

Get out early to enjoy those nice mornings. There’s plenty to keep gardeners busy:

* Warm weather brings rapid growth in the vegetable garden, with tomatoes and squash enjoying the heat. Deep-water, then feed with a balanced fertilizer. Bone meal or rock phosphate can spur the bloom cycle and help set fruit.

* Generally, tomatoes need deep watering two to three times a week, but don’t let them dry out completely. Inconsistent soil moisture can encourage blossom-end rot.

* It’s not too late to transplant tomatoes, peppers or eggplant.

* From seed, plant corn, melons, pumpkins, radishes, squash and sunflowers.

* Plant basil to go with your tomatoes.

* Transplant summer annuals such as petunias, marigolds and zinnias.

* It’s also a good time to transplant perennial flowers including astilbe, columbine, coneflowers, coreopsis, dahlias, rudbeckia, salvia and verbena.

* Feed camellias, azaleas and other acid-loving plants. Mulch to conserve moisture and reduce heat stress.

* Cut back Shasta daisies after flowering to encourage a second bloom in the fall.

* Trim off dead flowers from rose bushes to keep them blooming through the summer. Roses also benefit from deep watering and feeding now. A top dressing of aged compost will keep them happy. It feeds as well as keeps roots moist.

* Pinch back chrysanthemums for bushier plants with many more flowers in September.

* Tie up vines and stake tall plants such as gladiolus and lilies. That gives their heavy flowers some support.

* Dig and divide crowded bulbs after the tops have died down.

* Feed summer flowers with a slow-release fertilizer.

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