Gardening With Allen: Strategies, timing to avoid frost damage

I was going to plant tomatoes this week, but my neighbor suggested that I wait until May. There are plants in the stores already. Why should I wait?

Tomatoes and other warm-weather vegetables and flowers can all be damaged by frost. Our normal last frost date in Clark County varies from April 15 to early May, depending upon elevation.

Even after frost danger is past, plants such as tomatoes, peppers, squash, cucumbers and melons grow very slowly until temperatures are consistently in the 70s or above. Early-planted plants can become stunted and be passed up by vigorous later-planted ones.

A good way to get a head start is to buy and transplant small plants into larger pots and bring them inside at night. By alternating cool, bright outside daytime conditions and warm inside nighttime conditions, plants develop strong, compact growth. I start my tomatoes from seed and use this alternating warm night/cool day regimen to develop strong, sturdy plants.

Although tomatoes and peppers require a longer starting period, cucumbers, squash and melons only need about four weeks to develop a transplantable plant. By planting seeds in 3- or 4-inch pots now, you could have plants ready to transplant outside at the right time. Keep them inside until seeds germinate and then use the alternating in/out method.

Soil temperature is important: One of the main reasons why warm-weather vegetables grow slowly when planted early is cool soil temperature. Soil temperature is also important for seed germination. Warm-weather vegetables such as green beans and sweet corn are normally planted from seed directly in the ground. Corn will germinate at a temperature of about 50 to 55 degrees. The soil usually reaches that temperature by about mid-April. Green beans require a soil temperature of about 60 degrees. I usually wait until early May to plant beans.

Cool weather vegetables: Virtually all the root, leaf and flower bud vegetables are frost-tolerant and do well when planted early. Their seeds will germinate at 50 degrees or lower. Now is a good time to plant seeds of pea, carrot, beet, turnip, radish, onion, lettuce and spinach. Started plants of cabbage, broccoli, cauliflower, kale, and pak choi can be planted outside now.

Cool and warm flowers: Flowers fall into warm and cool categories, just like vegetables. Warm, frost-tender flowers should wait to be planted until May. These include impatiens, begonias, marigold, zinnia, coleus, geranium, dahlia, portulaca and sunflower.

All perennial flowers and most other annuals will withstand a few degrees of frost and can be planted any time now.

Now is also a good time to plant permanent plants such as trees, shrubs, vines, roses and lawns.

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