To shade or not to shade.....

[JoZoo]

What is your view about providing shading over cactus and suculents in the UK for the summer months? I personally want to leave all shading off and just add extra air by opening the doors & windows and providing extra fans. Previously the collections were shaded in the summer with white washed windows and probably 50% shading overhead.

So far on the hotter days the temperatures have reached 35. At what temperature would you decide to provide overhead shading to cool things down?

Cactus collections include Matucana, Copiapoa, Turbinicarpus, Mamilaria, Gymnocalycium, Melocactus as the majority. Some Gasteria which I have been told would benifit from some shade so could put these under the bench and also some Howarthia.

Also are there any signs I should look for to prevent scorch.

[matchat]

Personally I prefer not to shade and just make sure my greenhouse I'd well ventilated. I'm lucky that my garden gets quite windy so I don't need extra fans running. If you can keep fans running 24/7 that should reduce any risk of scorch.

I prefer to give my plants full sun as it produces better spination and harder growth. Anything a little more delicate goes under the bench or sits in the shade of a larger plant.

[Eric Williams]

I agree with Matchat, ventilation is the answer. Although I do shade one half or the roof ( south facing) with a fine garden mesh, but I have 2 automatic vents, a large fan going 24hours/day, and the door wide open, but the opening covered in the same mesh to prevent birds entering. Cheers

[iann]

I prefer not to shade, but on got days with unbroken blue skies and low humidity, it can be difficult to provide enough ventilation even with fans going. So on half a dozen days a year, I throw a couple of sheets over the greenhouse. The rest of the time the only shade comes from the natural Manchester weather.

Copiapoas are renowned for scorching, especially early in the season, but almost anything can burn if it is sitting in the sun behind glass without sufficient air movement to cool it. Some plants just plain can't take lots of strong direct sun, but they're quite rare in the UK. Gasterias might qualify, some Gymnocalyciums. I've noticed a number of cacti don't like strong sun when it is cool, but love it when temperature soar, G. mihanovichii is a good example.

[JoZoo]

I prefer not to shade, but on got days with unbroken blue skies and low humidity, it can be difficult to provide enough ventilation even with fans going. So on half a dozen days a year, I throw a couple of sheets over the greenhouse. The rest of the time the only shade comes from the natural Manchester weather.

Copiapoas are renowned for scorching, especially early in the season, but almost anything can burn if it is sitting in the sun behind glass without sufficient air movement to cool it. Some plants just plain can't take lots of strong direct sun, but they're quite rare in the UK. Gasterias might qualify, some Gymnocalyciums. I've noticed a number of cacti don't like strong sun when it is cool, but love it when temperature soar, G. mihanovichii is a good example.

That's interesting about them not liking it cool with strong sun. Could make life difficult on a chilly but sunny day

[iann]

That's interesting about them not liking it cool with strong sun. Could make life difficult on a chilly but sunny day

Some like it, some don't. My Lithops love cool sunny weather, but quite a few cacti don't (and quite a few do).

[Peter]

My 40ft greenhouse has eight roof vents, two opening vents in the end wall, a large double size door that stays fully open in the summer, a fan in the roof - and still Copiapoas burned in the clear Shropshire air. That's why I keep large bubble insulation
permanently fitted.

This didn't happen when we lived near Warrington but with the M6, M62, M56 and A580 East Lancs Rd close by, a yellowish filter kept the sun's rays from doing their worse. Our version of heavy traffic now is...two tractors.

[AnTTun]

Question hard to answer JoZoo, as you can see from previous posts. I guess most (if not all) forum members that replied grow their plants in glass GH. I keep mine on polycarb closed back porch and I still have to be careful which plants I keep close to polycarb. I had several of them badly burned. So its mostly hit and miss experience for each of us, depending on what kind of GH one has, it's location according to sun and surrounding houses, fences, trees. Then there is geo location, climate...

If you think you should shade, I recomment small trick: put a layer of white net first (closer to plants) then put another layer of dark (green or black) net on it. Dark will create shade but white will disperse remaining light better.

[Chris L]

When I had my old 6x4 I always left shading up as with one door and one window the temperature soon soared. When we had the really hot weather last year it was hitting the higher 40's*C.

When the garden was re-done over winter I got the builder to put a hole in the wall (see picture). There is a louvre vent on the other side of the wall in the back wall of the GH. Works a treat with the door and the vent open.

I hope to reduce the shading a little, but kept some because the plants have had it before.

[Martin]

I have the same greenhouse as Peter I find as its a commercial style greenhouse and as such much larger (20 ft wide) and taller (about 15ft at the apex) than typical domestic styles the larger air volume along with all windows ( 8 side vents and 10 roof vents) and large door open all the time I have not had any scorch and have no shading

I get full sun on the greenhouse during the summer form around 6 am through to about 5pm

I also think if the plants are in good health and growing well they are more resistant, if they are stressed, very dry at the roots etc then they are susceptible especially early in the year on new growth. In my old greenhouse (10ft by 20ft)I always used to put up shading in early spring and leave it up all year.