Bedding plants for flowers and vegetables are available as seedlings, known as transplants. They’re sold by garden centers, nurseries and through the mail. Carefully time your purchases according to local average weather conditions for planting. Purchased transplants can be temporarily sustained in a bright window or under energy-efficient grow lights if necessary.
When buying transplants, the condition of the plant is often more important than its variety. Transplants purchased through the mail (usually a unique heirloom variety not found locally) will often arrive appearing stressed and should be immediately planted according to the instructions provided by the grower. These transplants should quickly rebound to a healthy state.
A good transplant would be at least as wide as it is tall. It should have a stocky stem with dark colored (usually green), thick leaves and, if possible, it should not be flowering, although, if purchasing more mature transplants, they will likely be flowering. Choose the best, healthiest plants that are free of disease and insects. Avoid any neglected plants. Use caution when buying transplants after a cold, wet spring because they may not have been sold quickly enough. Avoid tall, thin and pale plants that have not received enough light or water. Also, some vegetables that are now sold as transplants are actually better when grown from seed sown directly into the garden.
The outdoor environment can be very harsh for a transplant. So, harden the transplants before planting to increase their chance of survival. Place them outdoors where they will receive direct sunlight but out of the wind for a few hours each day for a week. Gradually lengthen the amount of time outside each day. Move the plants inside at night if temperatures drop to near freezing. Keep them watered and plant them as soon after hardening as possible according to planting guides for the area. In windy locations, consider protecting transplants from battering winds.
For more information, see the following Colorado State Extension fact sheet(s).