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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Selecting and Planting Annual Flower and Vegetable Transplants

This article was published originally on 4/18/2012

Home gardeners will soon be buying annual flower and vegetable transplants from local garden centers and greenhouses. To help insure a successful start to the gardening season, select strong, healthy plants and harden them outdoors for a few days prior to planting. Proper planting is another key to success. 
 
Selection
 
Select short, stocky plants with dark green foliage. Avoid tall, spindly plants. Small to medium-sized transplants become established in the garden more quickly than large ones. Short, stocky vegetable transplants are often more productive than large plants with flowers or fruits. When selecting annual flower and vegetable plants, large transplants are usually not the best choice. 
 
Hardening
 
Annual flower and vegetable plants started indoors or purchased from greenhouses should not be planted directly into the garden. The intense sun and strong winds may damage or kill the tender transplants. Plants should be “hardened” (acclimated to outdoor growing conditions) before transplanting them into the garden. Initially place the plants in a shady, protected site. Then gradually expose the plants to longer periods of direct sun. Closely watch the plants during this period. If possible, check on them at least once or twice a day. Thoroughly water the transplants when the soil surface becomes dry to the touch. Move the plants indoors if strong winds, a severe storm, or an overnight frost threatens them. Transplants should be ready to plant after 6 or 7 days of hardening. 
 
Planting
 
Most annual flowers should be planted outdoors when the danger of frost is past. A few frost tolerant annuals, such as pansy, sweet alyssum, and snapdragon, can be planted two to three weeks earlier. Cabbage, broccoli, and cauliflower transplants can be planted outdoors in early April in southern Iowa, gardeners in northern counties should wait until mid to late April. Tomatoes, peppers, cucumbers, melons, and other warm season vegetables should be planted after the danger of frost is past. 
 
Carefully remove plants from plastic cell packs by gently squeezing the bottom on each compartment. Plants in plastic pots can be removed by tipping them on their sides and tapping the bottom of the pots. 
 
If possible, plant annual flowers and vegetables in the garden in the evening or on a cloudy day. Planting at these times lessens transplant stress and allows the plants to recover somewhat before being exposed to the strong, mid-day sun. Place plants in the ground at the same depth or slightly deeper (no more than ½ inch deeper) than they were in their containers. (Tall, leggy tomato plants can be planted much deeper than previously grown as roots will develop all along the buried stems.) Many annuals, such as petunia, snapdragon, salvia, and periwinkle, should be pinched back to encourage branching. Others, such as impatiens, are self-branching and don’t require pinching. It’s also advisable to remove flowers on blooming annuals. Blossom removal aids plant establishment. Vegetable transplants should not be pinched. 
 
After planting, water each plant with a dilute fertilizer solution. A dilute fertilizer solution can be prepared by adding a small amount of a water soluble fertilizer (such as Miracle-Gro) to one gallon of water.