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University of Illinois Extension

Summer in the Vegetable Garden

June 20, 2014

URBANA, Ill.  – Summer can be a hectic time in the vegetable garden, said a University of Illinois Extension horticulture educator.

“Heat, wind, rain, insects, squirrels and disease can make gardening difficult,” said Ron Wolford. “The following are some month-by-month suggestions to help you combat those summer hazards and produce a bumper crop of vegetables.”


Plant warm-season veggies: Warm-season veggies need warm soil and air temps. Plant or direct seed pumpkin, cucumbers, squash, and melons the first week in June. TIP: Check out the U of I Extension website, ‘Watch Your Garden Grow,’ at http://urbanext.illinois.edu/veggies/ for detailed information on growing vegetables.

Check for cabbage worms on cabbage and collards: Cabbage worms can do a lot of damage to cabbage and collards by chewing large holes in the leaves. The adult white or brown butterflies lay eggs on the undersides of leaves. Control by covering the plants with row covers or spraying with the biological control Bacillus thuringiensis (BT).

Attract beneficial insects: Don’t waste your money on buying a box of ladybugs at your local garden center. Ladybugs will fly away if there is not an ongoing food source for them. Attract beneficial insects and parasites by planting flowers in your vegetable garden. Some good choices are cosmos, coneflowers, dill, yarrow, tansy, fennel, marigold, zinnia, salvia, sage, and sweet alyssum.

Scout the garden for insects: Take the time to walk through your garden every couple of days checking for insects. Insects and insect egg masses can be found on the upper and undersides of leaves. Insect populations can increase rapidly. Aphids, for example, can go from a few to hundreds in a short period of time. Always identify the insect before deciding if treatment is needed. Call your local U of I Extension office for assistance in insect identification. TIP: Clean up the garden at the end of the growing season because insects will overwinter in dead plant debris.

Use organic mulches: Mulches help to reduce the evaporation of moisture from the soil and reduce weeds. Mulches help to maintain uniform soil temperatures. Organic mulches include compost, shredded bark, leaves, pine needles, cocoa bean hulls, and dried grass. Avoid using grass clippings that have been treated with pesticides. Put down a 2- to 4-inch layer of mulch around vegetable plants after the soil has warmed. TIP: Dig the mulch into the soil at the end of the gardening season. This practice will add nutrients to the soil and improve soil structure and drainage.

Install a rain gauge: Rainfall can vary over just a few miles in the summer. Installing a rain gauge in your yard will give you an accurate measurement of rainfall. Install your rain gauge in an open area away from your house and trees. TIP: Empty the gauge after each rainstorm.


Give your vegetables an inch of water per week: Vegetables need at least 1 inch of water per week. Water the soil to a depth of at least 6 to 8 inches. Do not water during the hottest part of the day. Water at the base of plants to avoid wetting the foliage. Wetting the foliage is an open invitation to disease. TIP: You will lose 50 percent of moisture applied through evaporation when watering between 10 a.m. and 3 p.m.

Watch for blossom-end rot on tomatoes: Blossom-end rot causes the blossom end of the tomato to turn brown and black. This is not a disease. It is a calcium deficiency caused by high temperatures and fluctuating soil moisture levels. It usually occurs on the first ripening fruits. Water tomatoes consistently with the equivalent of 1 inch of water per week to avoid fluctuating levels of soil moisture. Mulches also help to conserve moisture.

Watch for leaf spots on tomatoes:  Leaf spot diseases are common on tomatoes. Yellow or brown spots occur on the lower leaves first. Remove the infected leaves to prevent further spread. Growing tomatoes in cages and staking tomatoes helps to control leaf spots. Control tomato diseases by removing old tomato-plant debris from the garden and avoid wetting the foliage when watering. TIP: The best way to prevent vegetable disease is to buy disease-resistant vegetable varieties.

Watch for tomato hornworms:  Tomato hornworms are 3- to 4-inch long, green worms with white stripes and a horn at the rear end. If there are large enough numbers, they can strip a tomato plant of leaves. They are difficult to find because they blend in with tomato foliage. Sometimes you will not notice them until feeding has occurred. The easiest control is to pick them off and squish them with your fingers. TIP: If you see white bumps on the back of the hornworm, the worm will soon die. A parasitic wasp lays eggs in the hornworm. The eggs hatch and larvae feed on the worm. They eat their way through the worm’s skin and pupate, spinning the white oval cocoons.


Harvest onions:  Harvest onions when the tops have turned yellow and fallen over. Pull the bulbs and let them dry. Place the bulbs on screens or hang in small bunches for two to three weeks to complete the curing process. After drying, cut the tops back to 1 to 2 inches long and place bulbs in cool storage area with good air circulation

Protect tomatoes from squirrels:  Pick tomatoes when they show some pink color and bring them indoors to ripen. This will save the tomatoes from squirrels who like to take a bite out of ripe ones. To ripen tomatoes, place them in a paper bag. Punch some holes in the bag and fold the top over. The bag will help to keep some of the natural ethylene gas in place, which aids in the ripening process. Check them daily. TIP: You can also wrap tomatoes in newspaper for ripening.

Sow radish, lettuce, spinach, and chard in late August:  Leaf  lettuce, spinach, radishes, and chard can still be planted for a fall harvest. Prep the soil for planting and fertilize before seeding. TIP: Mix Lettuce ‘Black-Seeded Simpson’ with a red leaf lettuce variety like Lettuce ‘Red Sails’ and plant in late summer or early fall in empty areas of your veggie and flower garden. These colorful plantings make great salads and will survive hard frosts.

Plant a green manure crop: Sow a green manure crop in empty areas of the vegetable garden. Sow seeds of oats, rye, or buckwheat. Cut the plants back if they flower to stop them from self-seeding. The green manure crops can be dug into the soil in the spring. Wait two to three weeks for the crop to decompose before seeding or transplanting. Green manure crops will add nutrients to the soil and improve soil structure.

Start a compost pile: Late summer is a great time to start a compost pile because of the plethora of plant material available as the garden season ends and fall begins. Composting is a great way to turn plant material from your vegetable garden into a dark, crumbly soil conditioner. TIP: Check out the Extension website ‘Composting for the Homeowner” at http://web.extension.illinois.edu/homecompost/.

Source: Ron Wolford, Extension Educator, Horticulture, rwolford@illinois.edu

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