To grow a successful vegetable garden in northern Illinois--or anywhere--grow varieties suited to your area and plant seeds and/or transplants at the proper season. For example, during the short growing season in northern Illinois, plant tomato varieties that mature less than 70 days from transplanting. This way you'll be able to harvest as much fruit as possible before the vines are killed by frost. Don't grow crops that require more than 90 days to mature, such as sweet potatoes and peanuts; your season is simply not long enough for these long-season crops to mature.
Determine the dates of your average last spring frost and first fall frost. In most parts of northern Illinois the last spring frost will be approximately May 1st through May 15th. These dates will dictate the correct planting dates for vegetables.
Choose varieties suited for growing in northern gardens. Comb seed catalogs and choose varieties of vegetables that are quick-maturing, choosing hybrid varieties when possible. Hybrid varieties of vegetables are more reliable and usually bear their crops faster than open pollinated varieties. Vegetable varieties that have won the All-America Selections award are also good choices for northern gardens because of their outstanding performance in trials. Choose and plant vegetable varieties that are proven to have resistance to or tolerance of plant diseases. This can help to avert a total crop failure from pests or disease.
Plant hardy vegetables about four to six weeks prior to the date of your last spring frost, including brassicas such as broccoli, cabbage and collards. Lettuce, spinach and other salad greens; plus peas, radishes, onions and potatoes can also be planted at this time.
Plant tomatoes, corn, and squash on or near the average date of your last spring frost.
Plant peppers, eggplant, pumpkins, melons and sweet potatoes about 10 days to two weeks after your last spring frost.
Prepare the planting bed so that the soil is loose, friable and well-cultivated and the bed is free of rocks and large clumps of soil. Add a 2- to 4-inch layer of organic matter such as compost and peat moss to the surface of the soil to increase its fertility. Turn over the top layer of soil with a shovel to incorporate these organic soil amendments.
Provide young transplants and seedlings with consistent moisture. Spray or mist the seedbed daily and water small plants or transplants as needed to keep the soil moist and help reduce transplant shock. As the plants mature, provide them with the equivalent of an inch of rainfall per week.