Greenhouse & Indoor Gardening

How to Grow Effectively in a Greenhouse Year-Round

If the complexities of a needs analysis, the many choices of design and materials, and the selection of features and accessories haven’t scared you off yet, then this piece on greenhouse operations shouldn’t be all that intimidating. After all, this is where you get to put the gardening structure into use and reap the benefit of your investment.

Let’s look at the basics of greenhouse operation, keeping in mind that specific plants may require special care beyond the basics. Also, keep in mind that your climate and weather conditions will dictate to some extent how you operate your greenhouse. Factors like sunlight, humidity, wind, and soil can influence things like venting, watering, and air circulation.

Venting Heat and Humidity

The number one task of greenhouse operations is maintaining an environment that is conducive to plant growth. That means warm, but not excessive heat, and minimizing humidity unless your specific plant variety calls for high humidity. High heat will significantly shorten the life of your greenhouse film. High humidity tends to encourage pests and disease.

If you’re using manual ventilation methods, this will be a morning and evening chore. If you’re using automatic devices, then you’ll need to set the controls to open vents as the heat starts to reach what you’d consider an optimum temperature. Structures oriented to capture the prevailing breezes will have an easier time getting rid of excessive heat and humidity.

Taking care not to over water your plants will help reduce excess humidity. Moisture in the soil will tend to evaporate during the day, and if it’s not vented out, it will linger and promote pests and disease.


To be sure, you will need to water your plants. There are several ways to water plants in a greenhouse. Oddly enough, some greenhouse gardeners prefer to water by hand, that is, with a watering can. The idea here is that the amount of water can be carefully regulated as well as placed. This is important if you’re growing a wide variety of plants that have varying needs for water.

An alternative to hand watering with a watering can is to water with a hose. This can be messy as it tends to create splashing or spraying that in many cases is unwanted. Nevertheless, if you’re growing plants on racks or tables, instead of in the soil, this is a good alternative. For plants grown in the soil, there are better approaches.

One helpful means of watering is to use a drip system. One common type of drip system employs individual emitters along a line. Depending on the emitter used, the gardener can vary the amount of water that is emitted over a given length of time. Other systems use tubing with small holes that serve as an alternative to drippers.

Individual emitters are great for targeting specific plants, and they are a good choice for planting beds and permaculture in the greenhouse where the location of plants doesn’t change. Although the drip system can be reconfigured, this isn’t a chore that anyone would look forward to at the start of each planting season.

Drip tubing emits water every twelve inches or so along the length of the tubing. This type of drip setup is best for watering a larger bed of plants where the drip tubing can be laid in a snake-like pattern to distribute water throughout the bed. This type of dripping technique is especially useful for vegetable row crops like peppers, beans, and kohlrabi, where individual plants are spaced about the same distance apart as are the outlets in the tubing.

Whether using drip emitters or drip tubing, it’s best to find a way to run the supply line so it’s off to the side or overhead. This will keep unnecessary lines out of the growing area. If you place the supply line overhead, it will promote draining clear and that will avoid freeze damage during times of the year when freezing is a possibility.

Air Circulation

Air circulation inside the greenhouse is essential to minimize pests and diseases. With smaller greenhouses this isn’t as much of a concern since open windows, doors and vents can provide good circulation when there is a breeze outside. For large greenhouses, natural air circulation is a bit more challenging – much like trying to get air to circulate throughout your house. The use of large fans and air handling devices can help promote good air movement.

A supplement to forced air circulation can be had by orienting the greenhouse such that prevailing winds will naturally enter windows, doors and vents to provide air flow through or across the greenhouse. It should be noted that both flowers and vegetables benefit from air movement sufficient to cause plants to move. Such movement supports strong growth, blossoms and pollination.

Dealing with Animals

Even though a greenhouse is a relatively closed and controlled environment, occasionally the gardener will have trouble with critters. For greenhouses where plants are growing in the soil at grade level, burrowing animals can be especially troublesome. Ground squirrels and rabbits come to mind as animals that seem to delight in making a burrow right where you would like to grow your tomatoes, collards, or zinnias. The only practical solution is to make certain the greenhouse is sufficiently buttoned up to minimize the potential for these animals to enter.

Another creature that presents problems for the greenhouse gardener is the common field mouse. Mice are plentiful and always looking for a comfortable place to call home. What better place than a warm and sheltered gardening structure during cold and foul weather? Not only is there an ample supply of water, but many of the fruits, vegetables and plants growing inside can provide a nice meal. And, if there are no mature plants to nibble on, there is nothing better than finding a stash of seeds, or a flat or two of young seedlings. Mice are particularly destructive to young seedlings.

In addition to sealing up the cracks and crevices of your greenhouse, you’ll need to take some steps to eradicate mice. There are repeating mousetraps on the market, and several designs for homemade versions of the same. The traditional snap mousetrap is also highly effective. It’s likely that your greenhouse troubles are only caused by a handful of mice so after you catch five or six of them, you’ll likely find your troubles are nearly over.

Starting Seedlings

Seedlings are quite often started indoors. That’s a nice, protected location, but it can lead to a mess where you don’t want it. With a little effort, even a hobby greenhouse gardener can use their unheated greenhouse as a place for starting seedlings. This is my preferred method because it keeps the mess outside, minimizes transporting seedlings, and presents seedlings to bright sunlight which is essential for good growth. If you’re tired of leggy seedlings that enjoy the grow lights, but still stretch towards the window for better natural light, then use your greenhouse as a place to start seeds – it’s outside where they’re going to live anyway.

To start seeds effectively, you’ll need at least a seedling heat mat and an enclosure that acts as a greenhouse within a greenhouse. One approach to achieving this is to use a cold frame inside the greenhouse. You can also use a clear curtain of greenhouse film to seal off a small area dedicated to seedlings. Such an approach allows you to use a small thermostatically controlled electric heater to warm up the area surrounding your flats of seedlings.

For tabletop seedling starts, one could even do something as simple as using a clear covering over the table that holds your seedlings (under their own clear cover). This simple cover could make use of a frame to hold it away from your seedling trays, or it could simply be draped over the top of your seedling tray covers.

Just make certain that you monitor your seedlings frequently because a covered seedling tray will accumulate excessive moisture quickly. Also, remember that a clear covered seedling tray, inside of a clear covered enclosure, inside the greenhouse can multiply the effects of the sun – even in the dead of winter – and this can kill seedlings quickly if they’re left unmonitored during the day. Also, you might need to cover the whole operation at night with an old comforter or other such insulating blanket. This will help capture warmth from the seedling heat mat and minimize temperature swings experienced by the seedlings.

Pots, Raised Beds or Soil

There are three approaches to growing plants in a greenhouse: planting in pots; using fixed raised beds; and, planting in the soil at grade level. The choice is largely dependent upon your intended use of the greenhouse. Let me highlight the reasons why one might choose one or more of these methods for their greenhouse operation.

Pots are a good choice if you’re going to sell individual plants. Having them in a pot makes them easy to load up for sale at a marketplace. Pots are also a good choice if your greenhouse is something more akin to a living space, as you’ll likely want to rearrange things every now and then. They also work well if you expect to transplant seedlings to another place within the greenhouse, to a traditional outdoor garden space, or to a place within your home.

Raised beds are an excellent way to multiply the warming effect of the sun on the soil. This allows you to get a head start on the growing season. They also provide a large amount of thermal mass above ground, and this helps keep the interior of the greenhouse warmer during the night. Raised beds also clearly define the growing space, and they can make gardening a little less back-breaking as well. One of the drawbacks of a raised bed is that it cools rather quickly at night and during a cooler day, so they’re not the best choice for overwintering various plants.

Planting directly in the soil of the greenhouse is perhaps a more traditional approach, but it provides several benefits. First, planting directly in the soil allows the gardener complete freedom in terms of configuration. Second, it allows for easy large-scale rototilling and amending of the soil. Third, plants at grade level make best use of the natural soil warmth, so this is a good choice for bringing cold hardy varieties into the winter months.

Occasional and Winter Season Operations

My last suggestions with respect to greenhouse operations involve occasional use, and winter season greenhouse gardening.

As an example of an occasional operation, think of a very small greenhouse dedicated to sprouting and caring for seedlings. It could be a sort of “incubation station” that feeds the main open sun garden beds used during the summer. This could be the best possible use of a very small greenhouse simply because it gathers lots of light, it can fit just about anywhere, it’s easy to keep warm with a small portable heater, and the structure doesn’t allow sufficient room for much else. Some that I’ve seen allow you to walk in a few feet and turn around – a one person operation at best. If you have a very small greenhouse, this might be the best use of that “sun space.”

A large greenhouse, with or without a source of heat could be used as a protected gardening area during the winter, especially if you enjoy vegetable gardening. If you have a source of heat or a good way of capturing solar energy, you might think about this aspect of greenhouse operations – a year-round vegetable garden. Even if you don’t have heat generation or collection resources in abundance, off-season gardening is still possible if you grow cold hardy cultivars and get them started during the regular growing season so they’re freshly matured plants as winter arrives.

With winter season greenhouse gardening, you won’t be digging carrots out from under the snow; you’ll simply lift off row covers or open the cold frames inside your greenhouse and harvest your crops. The best part of winter season greenhouse gardening is that it makes good use of your greenhouse as a year-round asset, not simply a part-time season extender. Anytime you can get more use out of an asset you have you increase its value. That makes it a much more cost-effective asset right from the start.

Clair Schwan is an experienced vegetable gardener who grows over 100 types of fruits and vegetables in unheated homemade greenhouses and open sun garden beds.

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