Peter wrote:The draught (gale force) this creates in the greenhouse ... disrupts Mrs T's expensive coiffure on the rare occasions that she enters my haven.
1. Surely a welcome deterrent? - unless you are paying for the coiffure, in which case it becomes a matter of cost-benefit analysis.
2. Mrs. T. had very short hair, on the last occasion I saw her. If you are paying for its upkeep, does it represent value for money?
3. Reply carefully if she is likely to read this post, otherwise you can be quite frank. (I suspect you will be safe. )
Yes, getting the airflow exact to prevent scorch without some degree of shading (which even bubble wrap provides) is always going to be a challenge for the reason I mentioned - simply leaving a fan at the door is helpful, but not sufficient to ensure air flows evenly throughout the greenhouse across all sun-touched surfaces meaning there will always likely be some plants, or some sides of plants that are exposed to increasing temperatures as the sun beats down on it. I think for many here this is probably the most common solution- allowing the bubble wrap to take the edge off in terms of direct heating of the surface of plants to some degree, whilst relying on ensuring some degree of airflow to finish the job.
How high is your greenhouse by the way Peter, am I correct in remembering it's fairly long and a decent width, but around the 12ft or so in height? I notice that the dimensions of a greenhouse plays a fairly big part also in limiting scorch - a big open greenhouse with very high roofing like that seen at nurseries such as Southfields is sufficient to ensure shading is not even necessary, so I think a large part of the difficulty we face is also caused by the limited space for hot air to rise up and be replaced by cooler air from below in most consumer greenhouses also - lower roof clearance has the effect of trapping it somewhat. I know people like Gordon at Oak Dene are able to grow all but seedlings without even bothering with fans even with his slightly higher than is typical roof clearance.
I hope you don't mind me resurrecting an old thread.
I have been thinking about this debate about shading and the underlying question: why do we have to shade our cacti and succulents, plants that have full sun all day in their natural habitats?
Black people living in temperate climates will tell you that they too have to protect their skins form the sun in spring and summer while black people living in Africa don't have to. I think cacti and black people share a, not necessarily similar, mechanism that protects them when the sun shines all year round, a protection they lose in temperate climates.
The sun through glass concentrates the effect of the infra red and removes some of the uv. Uv would naturally stimulate the protective mechanisms. The heat is what does the damage. That’s why moving air is so important. Air us rarely still in the great outdoors.
Heather aka Hedge
.......you can grow a hedge that is vertically straight over ten feet tall (Alan Parsons Project)
It makes little difference if the temperature in a greenhouse is hotter than habitat temperature. There's always air movement 24/7 externally. No air movement with a cactus largely comprised of water leads to damage.
Also in habitat, shade may be provided for some of the day, day lengths nearer the equator are shorter than our long summer days and you always get a breeze
Heather aka Hedge
.......you can grow a hedge that is vertically straight over ten feet tall (Alan Parsons Project)
For winter-growing plants in northern Europe, the intensity and duration of light during the growing period is MUCH lower than it is in the plants' native habitats (mainly South Africa). As a consequence the new growth is quite "soft" and therefore prone to sunburn (conophytums in my case) when our weather improves in the spring. It may be that even plants which are resting during our winter, like most cacti, develop changes in their epidermis which make them more prone to sunburn when the sun actually shines strongly once more.