Tuesday, March 9, 2010

Cold Frames for Seedlings, Zone 6, Boston

I am going to be using a DIY  cold frame that I purchased from Ocean State for only $20...it's pretty cool. Stands about 5' tall and 3' wide with clear durable plastic, zippered, tent-like cover. I want to utilize it properly as I have never used one before. I'll post snip-its of info I am finding online re: usage. BTW I went back last nite, a month after buying my first one to buy another....got the last one! So excited, I'll post photos of it later.

Pay attention to temperature
While heat and humidity are important for germinating seeds, excessive heat (above 90°F) can damage fragile seedlings. A min/ max thermometer hung on an inside wall of the cold frame is a great way to monitor temperature fluctuations.Give seedlings an early start. Whether you are starting seeds in flats or sowing them directly into the soil, a portable cold frame provides the opportunity to get your plants going a few weeks early, and it eliminates the transplanting shock that many plants face because they will be better acclimated from the outset. If you are seeding in the early spring or fall, focus on cool-season plants, as they tend to have lower temperature thresholds for germination. Keep in mind that seedlings are more susceptible to extreme weather conditions than established plants. If you are sowing directly into a portable cold frame, have it in place two weeks prior to seeding to warm the soil for germination. Whatever method you are using to start your seeds, make sure to keep the seedbed evenly moist. Once seedlings have germinated, the cold frame should be vented more frequently to discourage damping off by increasing air circulation. If you start your seeds in a greenhouse or indoors under lights, you can start them a good six weeks earlier than usual and transplant them to a cold frame you’ve placed in your garden. It helps to have the cold frame in place at least two weeks prior to transplanting to warm the soil. Again, you will need to pay attention to the degree of sunlight, moisture, temperature, and wind. The frame also provides a windbreak while the plants are still small. Because you’re encouraging active growth, you will want to use a transparent cover of plastic or glass. The soil will dry out more quickly inside the cold frame than outside, so be sure to keep the soil moist, especially while the plants are acclimating to their new site. Keep in mind that more plants die of excessive heat and drought in cold frames than from cold damage. Proper ventilation is particularly important for cool-season plants. If you have established transplants, vent the frame when the outside temperature is 40°F or higher. If your plants are closer to the seedling stage, you may want to wait until the outside temperatures are 45°F to 50°F before venting.

Hardening off is simplified
When plants are moved from a warm, sheltered location—such as a greenhouse or indoors—into the garden, they must be gradually acclimated to fluctuations in temperature, sunlight, moisture, and exposure. Generally this is done by carrying the plants outside and back in again for gradually longer periods of time over the course of a week or two. The same effect can be achieved by opening and closing a cold frame over a five- to seven-day period.
The key to a trouble-free hardening-off period is to keep track of the extended weather forecast and plan accordingly. If I am moving out cool-season or young perennial plants from my greenhouse, I will wait for a stretch of weather where the lows don’t fall below 35°F. Even if the temperature drops after this period, plants hardened off and growing in a cold frame will be fine. For warm-season plants, I wait until the temperatures have stabilized and we are within two to three weeks of our last frost date. In general, wait until seedlings have formed multiple sets of true leaves and are well rooted before moving them into cold frames.Once the plants are packed closely into a frame, start venting the frame during the warmest part of the day, gradually increasing the length of time the frame is left open. If you are not able to tend to the frame during the day, try to time the onset of your hardening-off period with cloudy weather, and start by venting the frame just a crack, gradually increasing the open gap each day. As plants acclimate to cooler temperatures, more direct sunlight, and wind exposure, their foliage will often thicken and darken in color. New growth is also a good sign that the transition is going well and your plants are ready for their final move into your garden.  (This info was gathered from finegardening.com- 4 ways to use a cold frame) 
This is the key: Pay attention to the temperature. Keep it cool, not hot. Temperatures inside the cold frame should be below 75 degrees for summer plants, and below 60 degrees for plants that grow in spring and fall. Adjust temperatures by opening and closing the lid. A general guide is this: when outdoor temperatures are above 40 degrees, prop open the lid 6 inches; when the outdoor temperatures clear 50 degrees, open it all the way. Close the lid in late afternoon to trap the heat inside for the cool night. You can also buy automatic venting devices in some gardening catalogs. Be watchful for heavy rains and winds that could damage young plants or seedlings.
(Richard E, Palazzo, “The Gardenator,")

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