Can grow lights reduce hardening off time?

When used properly indoors, grow lights can considerably shorten the hardening off process. UV-enhanced lights prepare seedlings by mimicking the natural sunlight spectrum. They stimulate the production of cuticles and thicken stems before the plants go outdoors. I have cut the hardening period of tomatoes in half with this method.

When preparing for outdoor planting, the more time you can invest indoors, the smoother the transition will be. UV-enhanced light sources produce thicker leaf cuticles than ordinary light. Darkness and strain on the plant's stems (in flying the leaves) grow stronger stems. I position oscillating fans near light-bearing seedlings to produce these effects. The combination permits 50% less time in hardening for outside growth.

Watch for signs of light preparedness in the plants. Well-prepared seedlings are deep green with waxy leaves. Stems are tough and flexible. Plants show no wilting on the first exposure to the outdoors. I use 30 minutes of actual sunlight for this test before a full hardening.

Prepare transitional plants gradually, even with light preparation. Introduce them to two hours of morning sun after they have become accustomed to indoor light. Increase the exposure gradually, even though they are ready. For the first two days of outdoor work, please avoid exposing them to the noonday sun. This will prevent a regression in the growth of the plants.

Read the full article: The Complete Guide to Hardening Off Seedlings