Greenhouses are staples of agriculture – controlled environments designed to optimize conditions for growing our favourite plants, all without electricity or fancy temperature control systems. In fact, the idea is so simple and effective that it extends at least as far back as the early Roman Empire, where the emperor Tiberius’ favourite cucumbers were grown year-round under sheets of clear selenite. But despite their simple design and long history, greenhouses aren’t always the most intuitive to use. Here are 5 common mistakes to avoid if you want to grow cannabis (or any other crop for that matter) in a greenhouse.
#1: Starting with Poor Quality Materials
Greenhouses are useful for keeping a consistent internal environment and producing robust, healthy plants, but this’ll only go so far if you’ve got bunk seeds or weak clones. Make sure that your seeds aren’t light on the outside – ideally they should be dark brown and glossy, without being too dry or having visible cracks. If you’re using clones they should have strong white roots, sturdy leaves, and a solid green hue.
#2: Not Planning Ahead
From bushy 3 foot autoflowering indicas to towering expansive Hawaiian sativas, the cannabis plant has an enormous range of growth patterns. Know the limits of your space and plan the varieties you’ll grow accordingly, keeping in mind that you don’t want to crowd your plants too much. If you really want to grow a strain that won’t fit your space you can try pruning your plants aggressively, but this can stress plants and doesn’t guarantee good results.
#3: Starting at the Wrong Time
Sure, greenhouses extend the growth cycle of the plant, but that doesn’t mean you can start whenever. It’s always best to plant your seeds or clones in early June, when the days are longest and hottest. This ensures the plants will be well-developed by the time shorter days trigger their flowering stages. You may experience excessive growth if you plant too early, where planting too late can lead to underdeveloped plants. If you really want to try and get two harvests within the year, it’s time to research light deprivation techniques – but be prepared for some early mornings, late nights, and heavy labour.
#4: Overwatering and Overfeeding
Plants need water to survive, but too much can cause root disease that is often fatal to cannabis plants. Use your finger to assess the moisture of the topsoil before watering – if it’s moist to the touch, hold off until it’s dry. Use a soil hygrometer for more accurate measurements. And while piling on nutrients might seem like a good idea too much can actually be more harmful than not enough. Follow the instructions on your feed very closely, and if in doubt, wait until your plants are looking slightly underfed before refeeding.
#5: Heat and Humidity
Greenhouses are great for maintaining a higher temperature and humidity, which cannabis plants really like. However, excess heat and humidity creates a breeding ground mould, rot, and fungus – doesn’t sound great, does it? It’s best to invest in a thermometer/air hygrometer to measure ambient temperature and humidity. Check out this handy guide for ideal temperature and humidity ranges depending on the stage of growth.
Growing cannabis in a greenhouse makes life a lot easier and can extend your growing window by a significant margin, but that’s not to say it’s a one-size-fits-all solution. As with all growing, be sure to follow the goldilocks rules – not too hot, not too cold, not too damp, not too dry, not underfed, not overfed, but just right.