You bought a plant at the Master Gardener plant sale. Now what?
By Mary Fran McClure
WSU Chelan/Douglas County Master Gardener
Have you ever spent time in a greenhouse? It is a sublime place — warm, gently sunny, quiet and brimming with the energy of growing plants. I do love volunteering outside in the gardens our local Master Gardener program maintains, but I jumped at a chance to work in the greenhouse, up-potting seedlings for the Master Gardener Foundation Plant Sale on April 25.
In the greenhouse, the plant starts are kept indoors, watered daily and encouraged to grow without disturbance from temperature swings, wind, heavy rains or UV radiation.
For the past month, Master Gardeners have been germinating seeds, tending to the seedlings in the greenhouse and repotting the strongest plant starts into the pots you might have picked up for your own garden, if you attended the local Master Gardener plant sale. Reflecting on the spa-like environment your new plant grew up in, your job now, as caretaker of this plant, is to prepare it for the real world.
The process of acclimating an indoor plant to the outdoors, called “hardening off,” is a transition period that gives plants a chance to create natural defenses to environmental stressors. Plants that are ready for the outdoors have less “transplant shock” to overcome and experience continued growth more quickly than plants that have not built natural defenses prior to planting.
Hardening off is a simple process, but it does require moving your plants daily. For ease, keep them on a rolling cart. Locate a shady spot outdoors that will offer some dappled sunlight and protection from wind and rain, such as under a tree or a carport. The first day, roll your plants out to that spot for 3-4 hours in the morning, then bring them inside to a sunny window or under a grow light. The next day, increase the time to 4-6 hours. Continue incrementally increasing time outdoors, along with increased exposure to sunshine. Check the weather daily and keep plants indoors if the temperature will be below 45 degrees. Water once in the morning and ensure the plants do not wilt. By the end of week two, the plants can be left out overnight.
The time to harden off your plants is 1-2 weeks before the last frost, after which you can transplant your plants into the garden. In Chelan, Wenatchee and warmer areas of Chelan and Douglas counties, the first planting date is generally Mother’s Day weekend. In Leavenworth and other cooler areas, it is generally safe to plant around the end of May.
Keep an eye on soil temperature, either online via AgWeatherNet (https://weather.wsu.edu) or by sticking a thermometer into the soil in your garden; soil above 40 degrees is fine for cool-season crops, while soil above 60 degrees is safe for those precious, heat-loving tomatoes and other warm-season crops.
Why harden off your plants? It may seem like a burdensome extra step, but it is a step that will increase the vitality of your plants. Plants experience stress from their environments just like any other living thing. Plants that germinate outdoors are exposed to wind, ultraviolet radiation, temperature swings, and inconsistent exposure to water. Indoor plants have no need to develop any resistance to these stressors. Hardening off indoor plants over the course of one or two weeks is a gentle way to ease your plants (and yourself!) into the garden.
Source: South Dakota State University Extension, “Harden Your Transplants Prior to Planting Your Garden, bit.ly/sdsuhardenplants.
A WSU Chelan and Douglas County Master Gardener column appears weekly in The Wenatchee World. To learn more about your local Master Gardener program, visit bit.ly/wsucdmgprogram or call (509) 667-6540.