Building a backyard greenhouse can be a rewarding and worthwhile experience if you're looking to extend your growing season or grow plants outside your climate zone. Here, we'll demystify the hothouse hobby and provide some greenhouse tips.
Choosing a Temporary or Permanent Greenhouse
If you're looking to build a backyard greenhouse, you'll want to make a few upfront decisions before beginning any construction. First, how much time do you have to dedicate to your new greenhouse, and what does your budget look like?
The most cost-effective and easy way to extend your growing season without extensive planning is to build a temporary greenhouse. You can quickly construct PVC-framed plastic greenhouses, tunnels and hoop houses from relatively cheap materials in a single day over the weekend. Temporary structures can provide you with two to three additional months of the growing season, allowing for earlier planting and later harvesting.
Permanent greenhouses can be considered a level up from temporary greenhouse structures. Typically constructed of thick plastic paneling or glass, these structures require sturdier framing — especially if you live in an area with snowfall or strong wind events. Permanent greenhouses take more time to construct and, because of the sturdier materials, they typically cost more than temporary greenhouses. However, when well taken care of, they also last longer. Permanent greenhouses are also best set up to include metal or wood benches or tables. You can use these to elevate potted plants, allowing for a better handle on weed and pest control while also improving airflow.
Picking a Location for Your Greenhouse
Once you've chosen the greenhouse you'd like to build, decide where to place it. The first rule of thumb for any greenhouse is to find a suitable location with maximum exposure to sunlight. Greenhouses only function properly when heated by the warmth of the sun. This might sound obvious enough, but even partial shading from a nearby tree or large bushes can knock the temperature down relatively quickly.
Find a location in your yard where you have at least eight hours of full sun each day. Trim back trees and other large plants nearby for better exposure and to minimize potential damage to the structure from falling or scraping limbs and branches. If you do find yourself with too much sun, you can easily install a removable sunshade within the greenhouse to give a little protection — especially in southern climates or when growing more sensitive shade plants.
Controlling Your Greenhouse's Temperature
Most greenhouses function by passively capturing the heat from the sun and holding onto it for as long as possible. However, there are times when the sun's rays aren't quite strong enough — or, on the other end of the spectrum, far too strong. All plants have an optimal growing temperature you'll want to try to maintain to the best of your ability, whether by actively heating the greenhouse with a furnace or cooling it with air cooling systems.
Temporary greenhouses and smaller hoop houses are often heated and cooled by passive means: heating by the sun and cooling by opening the sides or ends of the structure to allow for excess heat to dissipate. This is the most economical way to manage a greenhouse, but in warmer climates — and especially with larger, permanent greenhouses — it isn't always enough.
A furnace is the most common way to actively heat a greenhouse, but it can also be achieved by running hot water under the soil or benches, allowing radiant energy to rise. This sort of heating is also beneficial because it doesn't blast plant leaves with hot, dry air.
Water coolers, rather than air conditioning units, are the best way to actively cool greenhouses. AC systems pull moisture out of the air and can dry out plants in the process. Water coolers add moisture to the air as they pull in warm air and pass it through falling water or moistened materials.
Monitoring Your Plants' Watering and Humidity Needs
Greenhouses not only hold in heat, but they also hold in humidity, which can be both beneficial and detrimental to your greenhouse growing aspirations. For example, an abundance of moisture is necessary for the health of tropical plants but can quickly ruin an entire collection of cacti and succulents.
Monitor your ambient humidity within the greenhouse, and know the particular requirements for the plants you plan on growing within your greenhouse. Try to maintain the correct amount through watering, evaporative cooling and misting systems. Also, keep in mind that the higher the humidity, the lower the amount of transpiration and evaporation. Too much watering can easily lead to waterlogged soils and eventual root rot.
If you plan on growing seasonal fruits and vegetables in your greenhouse, note that when you transfer plants from the humid atmosphere of a greenhouse to the lower humidity of the outdoors, plants can easily dry out, leading to quick wilting and burned leaf edges. Gradually decreasing humidity before moving your plants outside will greatly increase the odds of plants "hardening off" and growing successfully outdoors.
No list of backyard greenhouse tips would be complete without mentioning the inevitable barrage of pests that will occur within a greenhouse and how to manage them. Note the use of the word "manage." Greenhouses of all shapes and sizes will attract pests, and your goal shouldn't be to eradicate them completely.
Instead, set your goal at keeping their numbers manageable and sustainable using organic pesticides like neem oil, biological insecticide (BT) and insecticidal soap. Overspraying chemicals can lead to pesticide resistance, so it's best to use a variety of means, including the introduction of beneficial insects.
The most common insect pests you'll encounter within your greenhouse will be mealy bugs, scale, aphids and thrips. While these pests are difficult to completely eradicate, again, a pest management program will keep their numbers low without any harmful effects on your plants.
If you have more questions about building a greenhouse garden, explore Burpee's guide to greenhouse growing.