Master Gardeners: Ready tender starts for life outside

Q: Is there a foolproof way of hardening off plant starts? I usually end up forgetting them outside until they're frozen or sunburned.

A: Hardening off plants that you have started indoors is an essential step if you want vigorous growth when you finally plant them outside.

Surprisingly, exposure to the intense light from the sun can be as damaging to starts as too much cold. They must be exposed gradually to the increased light, wind and cold until they get used to it. Tender plants such as tomatoes, peppers, melons and squash, or any frost sensitive plant, cannot "get used" to below freezing temperatures, so they must be protected from frost until the weather warms.

Hardening off should begin at least two weeks before you hope to plant. It involves exposing your starts to longer and longer periods of outdoor conditions until they have developed the internal structures and processes to deal with the great outdoors. Start with 15 minutes of exposure to direct sun in a sheltered area and gradually increase the length of exposure each day. As long as your starts continue to look healthy, exposure time can be doubled each day. Plants should also be gradually introduced to cooler night temperatures and gradually increasing amounts of wind.

With the busy lives most of us lead, this process can be very frustrating. It is difficult to schedule life around your juvenile plant start's growing pains. More than one gardener has bolted out of bed in the middle of the night and run out on the porch to find their forgotten tomato plants frozen; it's very frustrating to see weeks of work down the drain -- or in the compost heap.

The following are suggestions for making the hardening off process easier and more successful for you.

* When daytime outdoor conditions are temperate enough, place your plant starts outside for an hour or so a day beginning when they are very small. Plants that are exposed to outside conditions from the beginning will need less coddling later on.

* Thoroughly water starts before putting them outside. Large plants in small pots need a lot of water on a warm day.

* Set a timer in the house or on your cell phone, even if it's only for 15 minutes. Program a reminder into your cell phone or an alarm clock at night to double-check before bedtime and frosty temps to make sure all is safely inside.

* To prevent sunburn, set plants in a spot that will get sun for a short time but will eventually be in the shade, such as the east side of the porch or garage.

* Lay a sheet of wooden lattice on four blocks and harden off plants underneath. This creates a semi-shady environment where starts can be set out for several hours from the beginning.

* Starts can be set out during the daylight hours under a double layer of spun row cover. This thin fabric may be purchased at a nursery or garden center, and can be laid right on top of the plants. Secure the sides and ends so that the fabric rests lightly on the starts and can not be blown off by the wind. After a few days, one layer can be removed, letting in more light. After a week, the final layer can be removed. Spun row cover also gives a degree or two of frost/cold protection.

* Set plants out where you will see them when you come and go and can monitor their condition.

* If high winds are a problem in your area, provide some shelter. A large rock or a heavy box, a fence or outbuilding, or a shelter from bales of straw on three sides will break the wind as your starts get stronger.

* A fan that gently moves plant starts while they are growing inside will create stronger starts from the beginning.

* If you're away from home during the day, consider investing in a cold frame with a glass or plastic door that automatically opens and closes to regulate the temperature inside. If the weather is hot and sunny, shade with a piece of lattice or shade cloth for added protection for the first few days of exposure.

* Plants purchased from outside racks or the greenhouse of a nursery or garden center are usually already hardened off. If they are inside the store when you purchase them, you should ask if they've been hardened off.

* Washington State University Extension Master Gardener Program is an organization of trained volunteers dedicated to horticulture and community service. Questions about gardening, landscaping or the program may be directed toward the Master Gardener Clinic by calling 509-574-1600 or visiting the WSU Extension office at 104 N. First St. in Yakima. New volunteers are welcome.

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