Wait until soil temperature warms to 65 degrees
These Juliet tomatoes are just the right size for planting -- if it were April. As it is, February is too cold, yet the seedlings were already on display for sale this past Wednesday. Kathy Morrison
Is it too early to plant tomatoes? Yes! It’s mid-February and still winter, no matter the daytime air temperature or how much sun. Ignore those tomato seedlings now showing up in nurseries; if planted in the ground now, they’ll only suffer.
But to know for sure about tomato planting time, feel your soil. More specifically, measure its temperature.
Soil thermometers, available at nurseries, are a handy tool that will prevent costly planting mistakes. Know which seeds and tender transplants need soil temperature-wise before condemning them to a frosty demise.
Right now, our soil is too cold for even cool-season crops to get comfortable. According to UC Davis’ weather stations, soil temperature at its Russell Ranch test site on Friday afternoon (Feb. 17) was 46.3 degrees, measured about 8 inches below the surface; 46.5 degrees about 4 inches down. Cool-season vegetables such as beets and lettuce need 50-degree soil for root development and growth. When soil is too cold, the seed can rot before it sprouts.
Tomatoes, peppers and other summer crops require soil at least 60 degrees to get started; they’ll still just sit there and not really grow, but at least their roots won’t feel like they’re freezing. To get off to a strong start, tomatoes prefer at least 65-degree soil when transplanted.
And that’s almost 20 degrees warmer than our soil is now.
When will our soil reach 65 degrees? Most likely in mid to late April, our traditional tomato planting time.
In the meantime, if you've already succumbed to the lure of those tomato seedlings, any plants that look ready to go into the ground can be transplanted into 1-gallon black plastic pots. Line the pots with several sheets of newspaper for extra warmth and insulation before filling with potting mix. The black plastic will absorb heat and help root development inside the pot – while our native soil remains cold for several more weeks.
In their cozy black pots, baby tomato plants can grow strong and develop a sturdy rootball. Once their future planting bed warms up into the 60s, transplant the seedlings – with rootballs intact – into their summer homes.
For a look at UC Davis’ weather station reports and soil temperature: https://atm.ucdavis.edu/weather/uc-davis-weather-climate-station/.
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Garden Checklist for week of April 21
This week there’s plenty to keep gardeners busy. With no rain in the immediate forecast, remember to irrigate any new transplants.
* Weed, weed, weed! Get them before they flower and go to seed.
* April is the last chance to plant citrus trees such as dwarf orange, lemon and kumquat. These trees also look good in landscaping and provide fresh fruit in winter.
* Smell orange blossoms? Feed citrus trees with a low dose of balanced fertilizer (such as 10-10-10) during bloom to help set fruit. Keep an eye out for ants.
* Apply slow-release fertilizer to the lawn.
* Thoroughly clean debris from the bottom of outdoor ponds or fountains.
* Spring brings a flush of rapid growth, and that means your garden is really hungry. Feed shrubs and trees with a slow-release fertilizer. Or mulch with a 1-inch layer of compost.
* Azaleas and camellias looking a little yellow? If leaves are turning yellow between the veins, give them a boost with chelated iron.
* Trim dead flowers but not leaves from spring-flowering bulbs such as daffodils and tulips. Those leaves gather energy to create next year's flowers. Also, give the bulbs a fertilizer boost after bloom.
* Pinch chrysanthemums back to 12 inches for fall flowers. Cut old stems to the ground.
* Mulch around plants to conserve moisture and control weeds.
* From seed, plant beans, beets, cantaloupes, carrots, corn, cucumbers, melons, radishes and squash.
* Plant onion sets.
* In the flower garden, plant seeds for asters, cosmos, celosia, marigolds, salvia, sunflowers and zinnias.
* Transplant petunias, zinnias, geraniums and other summer bloomers.
* Plant perennials and dahlia tubers for summer bloom.
* Mid to late April is about the last chance to plant summer bulbs, such as gladiolus and tuberous begonias.
* Transplant lettuce seedlings. Choose varieties that mature quickly such as loose leaf.
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