Hartley Magazine

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Tips for Growing Greenhouse Seedlings That Thrive

Struggling with supplemental lights and squeezing plant flats into your house or apartment can make growing seedlings a challenge–but greenhouse gardeners enjoy the benefits of planting in environments ideal for their purpose. Whether you grow under glass or not, here’s how to insure your plants turn out the best they can.

As in so many other things in life, timing is everything. It’s common to push the season and begin planting too soon. Try to wait; do the math to see how long it really will be until they go outside. Greenhouses simplify maintaining plants undercover, but once they’re ready to move, keeping them crammed in pots simply isn’t good for their health.

Correct spacing is also important. Even in the very beginning, sowing seeds too thickly doesn’t give seedlings the best start. Especially once they’ve moved onto larger containers, the space between plants critically affects growth. Tightly positioned plants will stretch, trying to reach the sun.

Always use a well-drained mix. Water can be added to dry soil, but soggy soils tend to remain that way and invite other problems. Even with well-drained mix, don’t overwater. Overwatering is probably the single most common reason for lanky, unhealthy plants.

Adequate light seems easy within glass walls, but don’t take it for granted. Ensure that no shadows are cast upon your seedlings.

Air circulation is often overlooked in small greenhouse environments. Use those greenhouse vents– they should be open on sunny days. A fan should also run at all times for thorough circulation—one of the best ways to avoid disease problems.

Grow plants at the correct temperature. In the case of many spring seedlings, this may involve additional heat. Check seed packets and catalogs for recommendations; the plants you’ve sown might benefit from bottom heat– an energy efficient and easy way to maintain (especially nightime) temps without running heat for the entire greenhouse. But make sure that temperatures are also not too warm. Ideal daytime temps for most seedlings are 75 º; 55-60º at night. If a few flats require special conditions, consider creating a “microclimate” with some clear plastic tenting and heat mats. Monitor during sunny weather so that conditions aren’t too hot. Once plants are big enough to transplant, cooler conditions are usually best.

It’s common sense, but in the thrill of spring planting these essentials are often disregarded. Have fun with your seedlings; soon it will be time to garden outside!