Andy Rideout column: A few tips for 'hardening' plants in the spring
This spring, many of you will grow your own transplants from seed. This is a fairly simple process that requires only minimal equipment.
In only a few weeks you can grow seedlings to a size suitable for planting into the garden, containers, or raised beds. Before you move your young, tender transplants to the garden, they must first be hardened or acclimated to outdoor temperatures, sunlight, wind, and other environmental factors.
Plants taken directly from a controlled environment to the garden most often scorch from sunlight and wind and will either die or be severely stunted.
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The hardening process, also called "hardening off," changes tender and succulent plants into tough plants with stronger stems and leaves capable of withstanding wind and sunlight.
This process also helps develop cuticle on the leaf and stem surfaces which reduces water loss. When transplants are the proper size, move them to a shady, protected location outdoors.
A few guidelines to hardening include:
Keep transplants in the shade, gradually move them into sunlight for short periods each day.
Don’t take out transplants on windy days or when temperatures are below 45 degrees (this includes cool season vegetables).
Bring transplants back indoors at night for the first few days unless temperatures are very mild.
Reduce watering frequency but don’t let plants dry out completely.
Don’t fertilize during the hardening period.
The hardening process should begin one to three weeks before your vegetable transplants are ready for the garden. The time it takes a plant to be completely hardened for planting depends on the conditions under which the plant was grown.
Don’t rush the hardening process since even if the transplant survives planting, growth and fruiting will be delayed and yields will be reduced. Let the condition of the plant be your guide.
Another way of hardening transplants is to place them in a cold frame. A cold frame is a simple structure that protects plants from wind and utilizes the sun for heat.
Cold frames allow the sun to transmit energy through its lid where it can be stored as heat in the soil floor. The heat is slowly released overnight to keep transplants warm.
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Cold frames are most often built above ground of treated wood, although permanent frames can be made of poured concrete or masonry blocks. Previously lids were made of wood and glass, but are more likely made of plexiglass or a double layer of clear plastic today. Doubling plastic creates a dead air space for additional insulation.
The lid should be hinged for easy opening as a source of ventilation and temperature control. Place cold frames away from trees, near a water source, and with a southern exposure.
Adjust the lid of the cold frame every few days to help harden plants. On mild, sunny days you may need to open the lid wider. When very cold temperatures are expected you should bring your transplants back indoors.
Cold frames can also be used for growing cool season crops (i.e., lettuce, radish) to harvest before regular planting season. You can also extend your growing season into November or December by growing the same crops in cold frames.
When hardening is complete, your plants can be set out in the garden. Transplant on a cloudy day or late afternoon and keep plants shaded for two to three days until they are established.
Even hardened plants may wilt when exposed to full sun at first though they generally recover in a few days. Keep plants watered as necessary. Seedlings grown in peat pots or peat pellets may be planted directly into the garden.
Break the base of the peat pot to improve root penetration and drainage and remove the top edges of the pot that extend above the soil line. These edges can act as a wick that moves water away from the root zone.
Growing your own vegetables from seed can be fun and rewarding just remember to correctly acclimate your new transplants to outdoor conditions properly.
P. Andrew Rideout is the University of Kentucky Extension Agent for Horticulture at the Henderson County Extension Office. You can reach him by email at pandrewrideout@uky.edu.
This article originally appeared on Henderson Gleaner: Kentucky gardening tips: How to 'harden' plants in the spring
