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Garden Help Desk: Follow these tips when utilizing a greenhouse

By USU Extension - Special to the Daily Herald | Jan 27, 2024
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With careful planning and efficient use of space, even a small hobby greenhouse can provide a nice harvest of vegetables or cut flowers.
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A high-tunnel greenhouse made with hoops and poly covering can be used long-term or as a temporary site to give tender vegetables a head start in the spring or an extended harvest in the fall.
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Even creative or improvised greenhouses must provide plants with the basics: adequate light, correct temperatures, good air circulation and room to provide the plants with good care.

We bought a greenhouse kit for Christmas this year. We’re putting it together in a few weeks so that we can start some transplants, but we want to make sure we aren’t overlooking something we need to know before we start growing our plants. Are there things we should do now to avoid problems later?

There’s actually quite a bit involved in producing healthy plants in a hobby greenhouse. Success in a greenhouse comes from a mix of knowledge, planning and attention. Here are some things you should research and understand ahead of time so you can make the best plans and choices as you’re putting together and using your greenhouse.

Heating and cooling: Most people assume that heating in the winter is a big part of having a greenhouse, but cooling on sunny days can also be a challenge. A greenhouse can overheat very quickly on a sunny day, even in the winter. At a minimum you’ll need a reliable vent. If you’re going to use your greenhouse in the late spring, summer and early fall, you’ll need some kind of cooling system in addition to passive vents. Keep in mind that the smaller the greenhouse, the bigger the swings in temperature and the harder it will be to manage the environment in your greenhouse.

Lighting: Direct sunlight is important. Most vegetables and flowers need a minimum of six hours of full sun. You can supplement with artificial lighting, if needed. There are lots of good LED lighting products available. Having a timer for artificial lighting will be very helpful. Do you want to grow plants that need shade? You can do this with shade cloth either over the greenhouse or suspended directly over the plants. If you can’t find shade cloth locally, you’ll have no trouble finding a wide selection of shade percentages online.

Managing humidity: Your vents can be helpful when humidity is too high. High humidity makes it easier for plant diseases to get a foothold in your greenhouse. If humidity is too low, that can be stressful for your plants, too. Some hobbyists raise humidity levels by hosing down the floor of the greenhouse. Others will use a small misting system. An inexpensive hobby weather station can help you keep track of the temperature and humidity in your greenhouse.

Proper watering: Watering influences everything from plant health and greenhouse humidity to pest populations and disease. Your plants should be watered thoroughly but only when needed. Frequent watering can leach out nutrients and contribute to root rot diseases.

Overwatering can also leave standing puddles on the greenhouse floor, raising humidity and providing a place for pests to thrive. Make sure your greenhouse floor has good drainage.

Drought stress can also become a problem if you aren’t keeping an eye on things. Plan to be in your greenhouse checking on your plants daily at first. Look at the plants and lift the pots to check for lightweight, dry soil conditions.

Pest control: Weeds and insect pests thrive in a greenhouse where there aren’t as many natural predators to control their populations. Actively check for pests and diseases frequently whenever you have plants in the greenhouse. There are limited pesticides and herbicides registered for use in greenhouses, so you’ll want to learn about the common greenhouse pests: aphids, whitefly, thrips and fungus gnats. Knowing about these pests and their habits and life cycles, as well as the most effective and greenhouse-safe controls, before you plant anything will make prevention and early control easier.

Timing your transplants: If you’re going to use your greenhouse to grow your own flower and vegetable transplants, you’ll want to time things carefully when you start your seeds or cuttings. Use a calendar to identify your transplant dates, learn how many days before transplanting you need for each kind of transplant you’re growing, and count that many days back from your transplant date. That day is the day you should start the seeds for that crop. Planning ahead will save you the stress of having plants that are ready for transplanting before the weather is ready or having plants that are too small to use when you need them.

Sanitation: Good sanitation in your greenhouse will prevent all sorts of problems. Keep things clean and organized, and get rid of weeds in and around the greenhouse when you see them. Remove sick plants as soon as they are noticed and scout your plants at least twice a week to look for pest problems, signs of disease and problems with your fans, vents and watering system. Clean and sanitize shelves and benches between plant projects.


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