By Mary Small,Urban Integrated Pest Management Agent for Colorado State University Cooperative Extension
Starting transplants in the home is a great way to grow certain varieties of plants that are not readily available as transplants in the nursery.
Some problems occur, however, when you grow your own transplants. Many homes are too warm and have inadequate light, resulting in soft, spindly and pale seedlings. Sturdy, healthy seedling are grown under high light intensities and fluctuating temperatures (warm days and cool nights). For example, desired daytime temperatures may be 70-75 degrees and nighttime ones, 50-55 degrees depending on the species.
One answer is to construct a special hotbed/cold frame structure. Using an unheated basement or other cool room, and adding solid warming cables and artificial light also works.
"Damping off" is another problem that often plagues seedlings. It is a fungal disease, caused by one of several soil-born organisms. Damping off may prevent seed germination altogether by plugging up the conductive tissue of a developing seedling. Seeds may be killed just as they are approaching full development. Using pasteurized soil or a soilless mix can help you avoid this problem. Providing correct temperatures, correct light and avoiding over watering are also beneficial.
Novice gardeners often plant seeds too early, in hopes of having large transplants. Unfortunately, these giants often develop growth and production problems. The transplanting procedure shocks plants. They have the best chance of recovering quickly when they are smaller rather than larger.
To grow transplants of the appropriate size, decide when you want to plant them outdoors. Find out the seed-to-transplant time and add seven to ten days for hardening off. Backtrack the total amount to time from your desired planting date and you have arrived at the planting date. For example, let's look at peppers. The goal will be to plant hardened-off pepper plants outside May 30. It takes 8 to 10 weeks to grow a pepper transplant, so that would be (using 10 weeks) March 21. After including 10 days for hardening off time, the planting date becomes March 11.
Hardening off is the next step. This process prepares the transplants for outdoor conditions and plants will struggle if not subjected to it. A few days before "hardening" starts, reduce the amount of water plants receive, but don't allow them to wilt. To harden, begin by putting plants outdoors in a protected area for a few hours, then bring them back in. During the next ten days, gradually increasing the amount of time they are outside and increasing their exposure to wind and sun. After they've experienced several days of 10 to 1`2 hours outdoors, leave them outside 24 hours a day for a couple of days.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010