Shading

[Werewolf]

This is really an attempt to be helpful to newer growers as those more experienced will be well aware of the dangers of excessive, hot sunshine, which we apparenly can expect over the next few days.

Despite being (semi-)desert plants, many cacti can scorch quite badly in the hottest parts of an English summer when grown in glasshouses and, unfortunately, such damage can take years to grow out (it moves down the plant with age rather than truely regenerating in most cases). The better the ventilation the less the risk but shading is the safest solution.

There are numerous transluscent or semi-opaque plastic-type sheets that can be hung but these are cumbersome, especially around spiny plants and/or time consuming if you have to clear off large amounts of staging. My preference is for the type of liquid applications that are supplied as powders in Lemsip-type packaging from most decent garden centres. Just add water according to the instructions and away you go.

I prefer to spray on using a standard greenhouse pressure sprayer, which creates a nice filtered light through the pebble-dashing effect. Wash the sprayer very thoroughly afterwards and it can be re-used normally. And remember to close windows and vents before applying - the stuff looks alarmingly like mealy if you get a little on a plant!

The application is waterproof and can be removed in the autumn by wiping off, although this takes a little elbow grease.

[Chris43]

That is a useful guide, and even in or less strong sun, I have found some species scorch. Surprisingly to me, it is the smaller Copiapoas that seem to be affected worst, and a few Weingartias. Maybe its their position in my greenhouse.

Reaching the ridge on my 10ft wide greenhouse isn't an easy job so cleaning it off is a bit more effort than it might be, so I prefer simply to keep my bubble glazing up all year round. It seems to do the job OK, with fans going, and save a lot of effort.

[Werewolf]

Surprisingly to me, it is the smaller Copiapoas that seem to be affected worst, and a few Weingartias.

Hi Chris

Yes, Copiapoas, particularly C. krainziana, were especially prone. For me, the other genera most affected were Gymnocalycium, Matucana and Thelocactus, generally those with the most epidermis not covered by spination but most cactus species can, as I'm sure you know, display signs of stress (purpling, shrivelling stalled growth). As you say, greenhouse position will have something to do with it and others may have different experiences.

[AnTTun]

Count Croatia in described conditions. Seems sun is getting stronger and stronger, I've noticed burns and epidermis changes even on old, quite spinated specimen. So I had to give up on exposing them to direct sun and keep them under polycarbonate roof almost whole day. Even wierder thing is: they don't mind that, no lack of growth or flowering.

[Bill]

Like Chris I simply leave the insulation up all year.

Bill

[lobman]

I apply shading to the greenhouse roof and south side in the form of stripes , three to a 2 ft pane . The idea is that as the sun tracks across during the day , the shading is off and on continuously ,a bit like passing cloud cover .
I have noted that spay on shading is available for polytunnels that returns to virtually see through when it is wet , allowing for more light transmission , I assume it could equally be applied by brush to glass

[Werewolf]

I have noted that spay on shading is available for polytunnels that returns to virtually see through when it is wet , allowing for more light transmission , I assume it could equally be applied by brush to glass

Hi Lobman

Do you have a brand name? It sounds like something I'd like to try.

On the subject of bubble wrap, it never really worked for me, although I know many people swear by it. It probably depends, like everything else, on what precisely you grow and the rest of the micro-climate of your glasshouse. I found it increased humidity and that certain species seemed negatively affected by it, namely the former Cochemieas and Mammillaria senilis (all of which stopped flowering) and Coryphanthas, Escobarias, most Sclerocacti and some Echinopsis/Lobivias and some Rebutias (which were prone to turning brown). Since I stopped using it, everything has been fine but, as I say, no two glasshouses are identical.

Also, because I heat to around 10C to placate the tender Brazilians, I found there was no worthwhile cost saving. I suspect this aspect might be very different if your aim is to keep the frost at bay or maintain, say, 3C.

[IanW]

Also, because I heat to around 10C to placate the tender Brazilians, I found there was no worthwhile cost saving. I suspect this aspect might be very different if your aim is to keep the frost at bay or maintain, say, 3C.

Huh? are you saying there's no cost saving to bubble wrap insulation the higher you heat your greenhouse or have I misunderstood your comment?

[Peter]

The spray type is 'Coolglass' and is very effective. I apply it with a used insecticide spray gun (the ordinary Bug Clear type).

I find it easy to remove at the end of the season by hosing the glass and then using a soft bristled sweeping brush. It is though, necessary to remove the guttering end stops to prevent the chalky residue getting into my water butts.

[Werewolf]

Huh? are you saying there's no cost saving to bubble wrap insulation the higher you heat your greenhouse or have I misunderstood your comment?

I don't think I said there was no cost saving, I said what I had found was there was no worthwhile cost saving, a subjective term I admit.

When you're heating to a higher temperature and also having to ventilate more, when weather permits, to accommodate the other species, the saving becomes less significant proportionally than if the bubble wrap does much more of the job for you. Comparing year with year is never a precise science without gathering all manner of data; all I can say is from my experience of my conditions, the difference was small, especially compared to the better results I have achieved without bubble wrap.

Some growers prefer to close up their glasshouses for the winter; I believe in ventilation.