The Benefits of Shade Cloth in a Greenhouse
I’m sitting in my greenhouse sipping a cool drink as I look outside. With the current heatwave this is positively the coolest spot in the garden right now. But it didn’t use to be that way. Scorched leaves, dry soil and wilted, bolting lettuce used to be the norm.
Things changed when we added shade cloth to our home greenhouse and now we are hooked.
In 2018 when we installed a shade cloth to the outside of our polycarbonate-covered greenhouse, we chose a black 60% shade cloth in a twelve-foot width and 20-foot length to tame the monster that is the summer sun.
Shade covers are listed on Amazon in various colours but they are all too small for our 16 x 20 greenhouse. Meanwhile, some of the covers listed are too big for our smaller 8 x 12 greenhouse or cover too much of the space. A cover over the entire surface including the sides is not necessary. It’s overkill in the shade department.
At high northern latitudes, the sun is high in the sky in summer, and the sun beats almost straight down in mid-day. We pulled about two-thirds of our cover over the ridgeline and onto the south side with about one-third of the cloth cover to the north side of the ridgeline. The fabric cover we chose covers the entire length of our 20’ house.
Commercial shade cover suppliers like Midland Industrial Covers specialize in commercial-sized greenhouses so minimal purchases are excessive for most home greenhouse growers unless you have neighbours to share the excess fabric with. Seams are easily sewn over the knitted fabrics and some sewers are talented at adding grommets too so this could be a small business for some enterprising greenhouse owners but not me. I bought my cover already sewn on the edges with grommets installed every 2 feet to make tie-down easy.
Covers with grommets every two feet give the most options for tie downs so the fabric doesn’t become a sail and blow away. The cloth I installed is UV stabilized so it can be used for several years.
When should you add a cover?
Apply shade cloth seasonally as soon as days are consistently hot. Last year we applied our cover in May. This year we put it up in early June. As soon as days cool in the fall the cloth is removed.
Why Apply Shade Cloth?
Shade cloth reduces heat buildup in the greenhouse and this cooling effect keeps the pest populations lower, the plants healthier and the people happier. Glass greenhouses tend to overheat more than poly houses so I suggest 70% shade cloth over glass and only 60% over polycarbonate houses.
You will save effort and water once you add shade cloth.
How do you apply it?
We orientated our greenhouse east to west so that the long side of the greenhouse is facing south and north. This gives us the most direct light during the low light days of winter. The easiest way to cover our house and reduce excessive heat is to run the cover on top of the length of the roof.
Helpful Husband (aka Keith) folds the cover carefully every fall and keeps ropes tied to end grommets so the folded cover is easy to pull open one side at a time.
Commercial greenhouses often use covers inside the greenhouse along wires running from end to end. This allows the cover to be pulled open or shut over the portion of the house that needs shade – such as a sitting area or an arugula or lettuce patch. It also allows you to quickly retract the shade if you get a long rainy or cloudy spell in summer and the soil is staying too wet too long.
Can Shade Cloth be left on?
During the summer I want less light and heat but the rest of the year I want all the light I can get. I put the shade cloth up seasonally so plants grow as fast as possible during the cooler period from September 15th to spring. I like the option of watching the weather and adding shade only when I really need it each summer.
If your shade cloth is suspended on wires inside the house, it can be left up and just pulled back and forth as needed. Otherwise, it is best to install and remove it to suit your climate.
What about tree cover?
If you have one of those magical locations where your mature tree shades your greenhouse entirely when it leafs out in late May and drops its leaves by early September you might not need shade cloth. You are one of the lucky ones.
The Beginning of a Happier Life
I’m standing in the greenhouse and we have just finished installing our shade cloth. It took about 30 minutes this year and the effect is instant. The fans have been running continuously in this overly sunny spring but they are suddenly quiet. The plants seem to have taken a deep breath and as I sink into my chair with a good book, I smile. This is going to be another good summer.
Adding shade cloth translates into saved labour. After watering morning and night for years during the summer, we suddenly have more time to relax and enjoy the greenhouse.
If you are looking to simplify your life, do it now. Save money on electricity and cooling fans and boost the comfort of your plants by adding shade.
Check out this tool from BC Greenhouse Builders for more information too!
More from Donna
For more great tips from Donna, visit www.donnabalzer.com.
You can also read Donna’s gardening books: No Guff Vegetable Gardening with Steven Biggs and her just released Gardener’s Gratitude Journal: Part Diary, Part Personal Growing Guide.