Extension Educator, Horticulture
Mother Nature bats last. And sometimes she carries a particularly big bat. About the time we think it's the last pitch of the bottom half of the last inning, we end up with an extra inning of winter. A few warm days in March and we are in the outfield admiring the grass while Mother Nature blasts a cold one over the fence.
Just in case you are as confused as the robins, here is a run down on spring planting.
First let's determine our frost dates. In central Illinois our average date of last frost is April 15 -20 with the later date for more northern counties. The date of last frost is May 15. The first vegetables that can be planted are the very cold hardy ones. These plants withstand freezing temperatures and hard frosts without injury and seeds will germinate readily in cold soils. They can be planted 4-6 weeks before average date of last frost so early March through mid-April.
Very hardy vegetables for extra early planting by seed include: collard, kohlrabi, kale, rutabaga, salsify, leaf lettuce, peas, spinach and turnips. Spinach and lettuce seeds may even be planted in the fall for spring crops. Hardy transplants include: cabbage, broccoli, Brussels sprouts, parsley, Irish potato sets (baby potatoes), onion sets (baby onion bulbs), asparagus crowns, and rhubarb and horseradish plants.
Frost tolerant vegetables can be planted 2-4 weeks before average frost date so mid-March through April. These vegetables withstand light frosts and seeds germinate in cool soils, but not as readily as the very hardy group. Frost tolerants include seeds of beet, Swiss chard, mustard greens, radish, parsnip, lettuce, carrot, arugula, green onions, Asian greens, and endive. Transplants of cauliflower, Chinese cabbage and leeks can also be planted now.
Early plantings of cool season vegetables produce the best quality vegetables. In addition many vegetables flourish and produce a crop before all the insects wake from a long winter's nap.
In contrast we should wait until mid-May for warm-loving vegetables such as tomatoes, squash, peppers, sweet potatoes, watermelon, okra, lima beans, eggplants, and cucumbers. These plants don't grow well and their seeds often won't germinate well during cool weather. Their seeds germinate best at warm 70 degree F temperatures.
Some annual flowers will withstand light frosts. These include: annual phlox, blanket flower, cornflower, cosmos, lobelia, globe amaranth, marigold, morning glory, pansy, petunia, pinks, strawflower, sweet alyssum and sweet pea. These are best planted after mid-April as seeds or plants.
Annual flowers and herbs that can be injured by light frosts include: ageratum, basil, cockscomb, coleus, flowering tobacco, geranium, impatiens, moss rose, nasturtium, periwinkle, scarlet sage, verbena, wax begonia and zinnia. Planting date for these is mid-May.
If you just can't wait to plant, there are ways to stretch the season for planting a few weeks earlier than usual by providing frost protection. Now before dreams of orange trees dance in your head realize frost protection will help only a few degrees. One innovation for early season vegetable production is the floating row cover. Row covers are a type of fabric made of white ultraviolet-light-stable spun bonded polypropylene plastic. They are very lightweight and allow air, light and water penetration. In less windy areas place the cover directly over the crop and allow it to float as the plants grow. In particularly windy areas a hoop support may be necessary. The protection provided may amount to a 4 degree F difference in temperature on frosty nights. Plastic vented row tunnels offer more protection.
Remember never work the soil when it is too wet. If soil holds together after squeezing in your hand then the soil is too wet. If you just can't wait to plant, broadcast the seed over the untilled soil and cover seed with potting soil or compost.