Thursday, May 13, 2010

Be sure to ventilate your greenhouses

Greenhouses, Cold Frames, Hoop Houses, and other season-extension technologies do a great job of allowing us to continue growing tasty local vegetables during the "off-months" of winter. However, with the arrival of warmer weather, and the Springtime sun is traveling ever higher through the sky, one must be careful to avoid too much heat. These spinach leaves scorched due to a combination of too much heat and strong sunlight hitting the leaves while there was still water from morning's irrigation beaded-up on the leaves. Spinach is a cool-season crop, so it loved the greenhouse during January and February, but even by April greenhouses get too hot for Spinach to thrive.

To avoid similar problems in your own cold frames and greenhouses, be sure to water as early in the morning as possible so that water can evaporate off the leaves gradually before the sun gets too strong. Also, be sure to keep air moving as much as possible in any cold frame or greenhouse. Sides that roll-up or down are great features if you are putting up a new hoop structure. Removable end-walls will allow the hoop house to continue to be useful well into the summer: eggplant, peppers, and tomatoes all do better with some shelter from the rain and the extra heat early-on, but you need to keep maximum indoor temperatures below 90* F. or so for the plants to continue to thrive into the summer.

If your greenhouse lacks enough vents to move air passively, you may need to employ extra fans to cool things off. Keeping air moving will also help reduce disease problems such as damping-off problems in seedlings (i.e.- Pythium, Rhizoctonia).

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