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Wednesday, March 11, 2009 09:00 am

Gardeners, start your engines. And cool your jets.

A guide to what you can plant when

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Lettuce is among the hardy plants that can be planted from seed early in the spring.
PHOTO BY BOB FILA/MCT

As temperatures get warmer most of us are starting to dream of the first juicy ripe tomato or the heavenly fragrance of a garden-fresh rose. While we may be ready to get out and garden, it may be a little too early to plant some vegetables and flowers. Understanding the growing needs of plants, and some garden lingo, will lead to a successful gardening project.

How early you can plant depends on the hardiness of the plant and the climate. The USDA plant hardiness zones divide the United States into 10 areas based on a 10-degree Fahrenheit difference in the average annual minimum temperature. The idea of the USDA map is that it provides an easy guideline for categorizing locations suitable for winter survival of a rated plant in an “average” winter. Central Illinois is located in hardiness zone 5B where the average annual minimum temperature is -10 to -15.

The USDA Plant Hardiness Zone map can be viewed on The United States National Arboretum website at http://www.usna.usda.gov/Hardzone/index.html. The USDA hardiness zone doesn’t take into account local variations such as soil moisture, soil type, winds, winter snow cover and other conditions which might affect the viability of individual plants.

Here are some important dates for gardeners to remember.

The average date of the last spring frost in central Illinois is April 15. This means there is a 50 percent or less chance of frost on this date. The frost-free date for central Illinois is May 12. The average date of the first fall frost is October 14.

While the early bird may sometimes catch the worm, when it comes to planting, patience is a virtue. Vegetables and annual flowers are classified by their ability to withstand frost — very hardy, frost-tolerant, tender and warm-loving.

Very hardyplantscan withstand freezing temperatures and hard frosts without injury. They are usually planted four to six weeks before the frost-free date in the spring. For zone 5B, average planting dates are March 25 to April 10. Potato tubers and onion sets can be planted. Collards, spinach, peas, lettuce and turnips can be planted from seed. Very hardy flowers include pansy and ornamental cabbage.

Frost-tolerantplants can withstand light frosts andcan be planted two to three weeks before the frost-free date. For zone 5B, suggested planting dates are April 10 to April 25. Cauliflower, cabbage and broccoli can be planted as transplants. Carrots, beets and radishes can be planted from seed. Frost-tolerant flowers include calendula, sweet pea and snapdragon.

Tenderplants are injured or killed by frost, and their seeds don’t germinate well in cold soil. These plants can be planted on or after the frost-free date. For zone 5B, average dates are April 25 to May 10. Snap beans, sweet corn and summer squash can be planted from seed. Tomato transplants can be planted. Tender flowers include verbena, petunia and nicotiana.

Warm-lovingplants cannot tolerate cold and they require warm soils for germination and good growth. They should be planted one to two weeks after the frost-free date. For zone 5B, dates are May 10 to June 1. Warm loving vegetables need warm temperatures and warm soil before planting. Vining vegetable crops such as watermelon, cucumbers, winter squash, pumpkins and muskmelon can be planted. Pepper, eggplant, okra and sweet potatoes should also be planted.

Jennifer Fishburn is horticulture educator with the Sangamon-Menard Unit of the University of Illinois Extension.

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