Hardening Off Those Plants

Curious about what "hardening off" means and why it's important? Here's a blog from our archives to help you prep your cold-season transplants for the great outdoors. 

Plants need to be hardened off before being transplanted. What does this mean? It is the process you take them through to get used to direct sunlight, wind, cold, heat, dryness, and any other weather conditions they will be asked to live through during their lives. When plants are started in the greenhouse, in trays or pots, their world is sheltered and comfortable; food is readily available in the compost-fortified soil, and the temperatures are carefully regulated. Once it is time to go out into the harsh world of the garden, the goods and services become a little more scarce for those baby plants and they go through a bit of withdrawal known as "transplant shock."  Hardening them off gives them a gradual adjustment to this new world.  It is best to start out by putting the plants outside for a few hours, and then bringing them back in; this gives them a small taste of direct sunlight. In any greenhouse, the plastic film filters out 10 to 25% of the sun's rays and the tender plants are literally sun-burned when they first encounter that unmediated light.  Here is how I do it at my house. When you buy plants that were grown by Red Wagon Plants, they have already been hardened off and you can put them right in the ground. The following method is important to follow if you are working with plants that you know are not hardened off yet.

Once they have gotten used to a few hours of sunlight at a time, they can stay outside overnight, but under a protective row cover.

The cover comes off in the daytime and the plants are acclimated to being where they will be planted for a few days.

If the temperatures drop down below freezing, cover them again. Cold hardy plants such as broccoli, cabbage, kale, hardy lettuces, hardy herbs, escarole, scallions, onions can take a frost without a problem, but they will do it with more grace and strength if they have been gradually introduced to those temperatures.

Once the plants have had a few cold nights, under cover, they can have a couple more nights without cover, and then are properly hardened off and ready to go in the ground.

It's also a good idea to give cold-weather transplants a little extra compost or a fish/seaweed emulsion watering at transplant time. It is hard for plant roots to uptake nutrients in cool weather and this will aid their transition as well.

Don't Fear Frost! Extending Your Growing Season

Here in Vermont, we can count on just a few frost-free months. But with a little bit of planning, strategic planting, and getting the right tools, you can harvest through a bit of frost and snow. But by planning out crop planting so that crops are mature before the short days and cold weather hits, you can then protect them and harvest them well into winter.

Row covers such as reemay are usually used with hoops made of #9 gauge wire so that the fabric does not rest right on the plants. These covers breath and come in various weights. They allow light and water in, but raise the temperature of the soil and air inside the cover.

Cold frames are simple boxes that are filled with good quality soil and are covered with windows (called "lights") or clear plexiglass or sometimes plastic. They are used for season extension, plant protection, as mini-greenhouses, and as a place to overwinter tender perennials. The covers are closed at night and opened on sunny days. Lettuce, spinach, hardy greens, and herbs can be grown most of the winter in a hot bed with a south facing light. "Hot beds" are deep cold frames that hold a thick layer of manure below the soil. As the manure decomposes, it lets out a tremendous amount of heat which keeps the frame very warm at night even in the winter. Cold frames can be made out of wood, straw, stone, concrete with old storm windows on hinges. The windows must be small enough that they can be opened and closed easily by raising them up and propping them with a stick.

Straw mulch is a great way to extend the season for vegetables such as kale, spinach, carrots, beets and other root crops. Once the crops are matured, a very thick layer of straw around the base of the plants will keep the ground from freezing so that the roots may still be harvested. The straw also keeps the top of the crops from freezing in extreme temperatures. Spinach can be overwintered under straw so that an early spring crop can be eaten. Kale lasts well into winter and is also helped by a deep straw layer so that the cold wind does not completely dessicate the leaves.

Every home garden has microclimates. It is a good idea to take advantage of these when planning the fall garden. A south-facing foundation wall is a great place to prep a small area for greens and herbs that will be well sheltered from cold, northern winds. It's a good place to situate a cold frame as well and to plant it with radishes, greens, and other crops that will benefit from the micro climate.

Containers are another great way to extend the season. Herbs, greens and lettuces can be planted in pots, apple crates, milk crates, or window boxes and moved inside when the weather gets too cold. While they might not last all winter long, they will certainly give you some fresh eating for a few months longer...all you need is a sunny spot or some simple grow lights. Thyme, parsley, rosemary, and sage all do well in containers in the home and will last all winter. Kale and lettuce will last up to 5 or 6 weeks longer than they would outdoors.

Photograph by One Green Generation . Creative Commons license.