Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Sunburn [was Clivia/Kaffir Lily]
In article ,
Dave Poole wrote: Clivias are extremely susceptible to exposure from direct sun if they have been kept shaded. Your plant's symptoms are completely typical of one that has been severely burnt. ... This is something that we have discussed before, but I still don't understand the mechanisms, and so am asking for clarification and cross-posting. Here is what I understand the situation to be. The annual peak intensity of the sun in the UK is perhaps 70% of the daily, clear sky, peak intensity in the tropics, perhaps less. The ultraviolet levels are a LOT less, but I haven't been able to find what they are - let's take them as 40%. And, of course, even those figures apply to (typically) half a dozen days a year in the UK - the average daily peak in summer is much lower. My experience is that 'burning' damage is almost always caused by those few days, and that the sun levels on a 'Phew! What a scorcher' day might be 50% higher than on a typical 'hot' day in summer. This is because our sun levels are primarily controlled by atmospheric absorption, not sun angle. Is that your experience? I believe that the problems caused by sun through glass are mainly surface heating, because it is typically associated with slow air movement, is much more serious close to the glass than a distance away, and 1/2" air gap K glass double glazing does not seem to cause the effect much. Can you confirm or deny this? I don't have a clue what the primary 'burning' effect on plants is (i.e. ultraviolet or surface heating) and what the 'tanning' effect is. But they assuredly exist. Can you clarify those at all? Regards, Nick Maclaren. |
#2
|
|||
|
|||
Sunburn [was Clivia/Kaffir Lily]
In article ,
Nick Maclaren wrote: I don't have a clue what the primary 'burning' effect on plants is (i.e. ultraviolet or surface heating) and what the 'tanning' effect is. But they assuredly exist. Can you clarify those at all? Glass very effectively absorbs UV so it doesn't reach the plants at all. So any damage in a closed greenhouse is likely thermal damage. There are specialty quartz glasses that transmit some UV, but they are very expensive. Some clear plastics absorb more UV than others, but most that are produced for outdoor use include additives that intercept UV in order to delay the breakdown of the plastic itself. Having inadvertently damaged innumerable transplants over the years when they got zapped by sun before they hardened off, to me the damage looks quite different when fresh from that caused by thermal burning or freezing. In the latter, the whole tissue looks "cooked". In the former, it seems like chlorophyll is selectively destroyed, so you get patches of paper white tissue. Of course, in both cases the tissue later browns and dries out, but the appearance of fresh damage is distinctive, to my eye at least. Most of the plants I've seen injured by heat (from fluorescent light ballasts), freezing (but it was warm when I went to bed!) and sunburn (it was supposed to be heavily overcast today!) were young tomato, pepper and cucurbit plants, all of which have thin leaves that are not flat, so the distribution of the damage on the leaf surface for sunburn might be different for the flat, thick leaves of Clivia. Disclaimers: I haven't seen the picture of your Clivia. I'm in Toronto, Canada, where we have a continental climate somewhat modified by Lake Ontario, so my gardening practices are no doubt different from those of the readers of uk.rec.gardening. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Clivia-4939-(Clivia miniata) | Garden Photos | |||
Clivia Miniata hybrid --- Kaffir lily | Garden Photos | |||
Sunburn [was Clivia/Kaffir Lily] | United Kingdom | |||
Sunburn [was Clivia/Kaffir Lily] | United Kingdom | |||
Clivia/Kaffir Lily | United Kingdom |