AMES, Iowa – Some vegetables are planted in the garden using small plants (transplants) rather than seeds. This is standard practice with warm-season vegetables like tomatoes, peppers and eggplant and is becoming the practice with cucumbers, squash, cantaloupes and watermelons because transplants shorten the time by several weeks between planting and harvest. Horticulturists with Iowa State University Extension and Outreach provide answers to questions that will increase gardeners’ success with transplants. Contact Iowa State Hortline at email@example.com or 515-294-3108 to have additional questions answered.
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.
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 location. 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 six or seven days of hardening.
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.
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 in mid to late April. 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.