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Frost-free date and gardening       Send a link to a friend

By John Fulton

[APRIL 3, 2006]  While 70-80-degree temperatures get us used to spring and summer, we may be jumping the gun on planting warm-season garden items. Many annual flowers, tomato plants and other warm-season plants should not be set out until after May 10.

When we look at our average frost-free date, we see that it is April 25. About half the time in the last 30 years, the average last spring killing frost has occurred by this date. That also means that about half the time it hasn't. Last year was a good example of a late-season freeze.

Those selling transplants love those of us who like to buy these plants in mid-April. More years than not, they get to sell us at least two sets of transplants. Of course, all bets are off if you use protective covers, such as milk jugs, row covers or wall-of-water types of protection.

Usually it is just as easy to wait until the recommended date, and that would be after the range of April 25-May 10 for green beans, sweet corn and tomatoes. These are all considered "tender vegetables."

Melons, peppers, pumpkin and squash are considered "warm-loving" and should be planted in the range from May 10- June 1. Pumpkins planted for Halloween jack-o'-lanterns should be planted about Father's Day. These pumpkins will get ripe too quickly for use in late October if planted the normal time.

We are getting quite a few questions about fertilizing a garden. The normal rule-of-thumb rate (without soil test information) for fertilizing flower or vegetable gardens is about 15 pounds of 10-10-10 per 1,000 square feet. If you are using 12-12-12 or 13-13-13 fertilizer, use about 12 pounds per 1,000 square feet. Soil pH may need to be adjusted due to the addition of lime and sulfur, which are acidifying. Generally, about 4.25 pounds of lime neutralizes the acidity from 1 pound of nitrogen or sulfur. Beware of pH requirements for different plants before you go out to apply lime. Surrounding plants are also affected. Examples would be blueberries, rhododendron, azalea, pin oaks and many evergreens.

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One of the more popular questions, at least during the growing season, concerns how to prevent the leathery rot on the bottom of tomatoes. The leathery rot is called blossom end rot. It is caused by a calcium imbalance in the plant. You could apply some lime to the area where tomatoes will be planted. Lime supplies calcium. The more reliable method is to mulch tomato plants well. This evens out the soil moisture available to the plants. The alternative is watering on a frequent basis. See the precautions in the previous paragraph on too much lime.

Soil conditions permitting, it is time to seed things such as asparagus crowns, leaf lettuce, onions, peas, potatoes, radishes, rhubarb plants, spinach and turnips. Give it another week or two and it is time to plant such things as broccoli, cabbage and cauliflower. As with most things, a little bit of preparation goes a long way in preventing problems later on.


  • It is time to get the crabgrass preventer on, but don't apply it if you seeded your lawn.

  • It is time to mow already. Remove no more than one-third of the leaf blade at a time to avoid raking or catching clippings.

  • Cut back butterfly bushes to live material, with a 10-inch maximum height.

  • Harden off vegetable transplants.

  • Cut back ornamental grasses to a height of 4 inches or so.

[John Fulton, unit leader, University of Illinois Extension, Logan County Unit]

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