Whether you’re a hobbyist or starting a small business, the decision to build a greenhouse is an exciting step for your garden. Greenhouses extend the growing season, allow a controlled environment for plant propagation and provide the opportunity to grow tropical and ornamental plants that otherwise wouldn’t grow in your climate.
There are hundreds of kits online that make the construction simple, but some determined gardeners prefer to build their own using new and salvaged materials. Regardless, once you finish building your greenhouse, proper maintenance is essential to ensure that your plants and building stay healthy, clean and productive. Below are a few tips for new and experienced greenhouse owners.
Site Design: Orientation
The orientation of your green house building has a major impact on temperature control, energy efficiency and the success of your plants. In the U.S. it is best to orient your green house with the longest side facing south or southeast to maximize sunlight. However, assuming you have limited space, the priority would be to select an area that is flat, well-drained and away from trees, buildings and fences that would partially shade your building or drop material onto your roof.
Size your building based on your available space and expected needs. However, keep in mind that rectangular buildings facing the fun will heat and ventilate better. Gardening blog, Chelsea Green recommends a ratio of 3:1. In northern climates that receive snow, green houses must have peaked roofs to avoid heavy snow accumulation. A slope of 6/12 is ideal.
Site Design: Building Materials
Purchasing a hoop house or green house kit might seem expensive upfront, but for those with less construction experience, these kits are a great option because they allow customers to avoid time consuming shopping and salvaging for materials.
For those who prefer the DIY approach, ensure that salvaged materials are thoroughly inspected for signs of mold, mildew, fungus or toxic chemical treatments. Metal and wood are the most popular materials for the building frame.
Glass is the most expensive and heavy material, but some gardeners use recycled windowpanes for their green houses. Greenhouse polycarbonate is a cheaper plexi-glass material that is resistant to UV sunlight and lasts longer than plastic. If using plastic, select thicker sheets that have UV protection but remember that the thicker the plastic, the less sunlight your plants receive.
It is best to have a clean, controlled and well-draining floor. Gravel is the easiest option, but some gardeners prefer concrete.
Site Design and Maintenance: Temperature Control
The purpose of a green house is to have a warm, temperature-controlled environment for otherwise fragile plants. However, hotter is not always better. High temperatures can dry out and distress plants, so the interior temperature should never be hotter than 90 degrees Fahrenheit. To control your temperature, use fans and windows to encourage cross ventilation. Check the temperature inside different areas of the greenhouse at various times throughout the day and night. Fans with timers are a great way to control the temperature during times when the greenhouse consistently gets too hot. Never use an air conditioner as this will pull too much moisture from the atmosphere.
Remember that even within a small greenhouse, microclimates exist. Pay attention to which sections of your greenhouse get hotter. For example, cold air sinks. Fans will help keep warm air circulating, but select the location for plants based on what they need. Plants that need more sun can go on the top level, while plants that prefer shade can be placed below.
According to Chelsea Green, “the southwest corner will usually be the sunniest and hottest quadrant of the greenhouse because it receives the most sun exposure. The northeast will be cooler and is a good place for a propagation table or washing station.”
Maintenance: Clean and Green
Yes, it is full of plants and dirt, but a greenhouse should be clean and orderly – don’t let it turn into a jungle! Regularly clean and maintain the space and sterilize all tools. Clean floors, wipe down walls and clear debris from the roof. Dust the fans and clean gutters. Occasionally check all irrigation hoses, nozzles and devices for cracks and clogs. Undetected leaks or standing water will introduce condensation, mold and mildew.
Periodically prune plants and use trellises to encourage circulation and proper use of space. Don’t allow plants to over grow and compete each other.
Maintenance: Pest Control
Although the purpose of a greenhouse is to create a climate and pest-controlled environment, pests love to have a comfy space with a roof over their head too. If not detected early and controlled properly, pests like fungus and whiteflies can rapidly spread to all your plants. Thoroughly check new plants before introducing them to the greenhouse. Spot check existing plants frequently for signs of bugs and diseases. Remove pests by hand, quarantine effected plants and trim diseased leaves as soon as possible. Remove effected leaves and trimmings from the greenhouse right away.
Focus on keeping healthy, happy soil, which will help the plants be resilient to disease. Regularly add compost, compost tea or fish emulsion to your soil. Rotate the location of plants to discourage pests from settling into a permanent home.
Natural Prevention Remedies
Spraying herbicides, even organic herbicides, is generally not a good long-term solution, particularly in small greenhouses. With limited ventilation, sprays tend to accumulate in the soil at levels that are toxic for plants. The following natural remedies can be used to control pests and fungi:
Steeped and cooled chamomile tea is a natural anti-fungal that works great to prevent damping off and is safe on young plants. Nettle tea helps prevent mildew on leaves and mold in the soil but is best for mature plants. Rhubarb tea mixed with castile soap helps control aphid, mite and whitefly populations on non-edible plants.
Citrus peels boiled in water can be sprayed onto white flies to reduce their population.
Lady bugs are available for purchase and mail order and are a great natural predator for aphids.