Leaf burn is a very much talked topic especially among novice Jm’strs and avid growers as well. The facts are blurred with some folks having little problems with this phenomena and others a constant problem .
It is a fact that some trees are more susceptible to this than others mostly those with variegated leaves ( white as the variegation ) and those of lighter color especially the yellow leaf varieties. But many others will burn and the cause is curious since it varies so much.
It is also a fact that leaf tip and leaf burn in general seems to be less prevalent or simply “goes away” as the tree ages. But this is not always the case. I have had 15 year old Bloodgoods burn severely in mid summer heat in part shade .
Add to all of this some folks in various parts of the country have little problem with this on then same cultivar that others have a more major problem .
Now granted some of this may have more to do with the anal personality of the individual JM’ster .. in that some may see a bit of leaf tip burn as nothing more than “Ehhh” while others become obsessed with it, trying various potions and formulas to stop it, almost always fruitlessly.
My first inclination was that it was a humidity based event and the heat itself was only a part since it seems to be more prevalent in humid areas of the country . Now I think it is a combination of climatic and area conditions as well as what period during the season this occurs . Basically there is a good possibility that it occurs with the other conditions specifically during dormant or nearly dormant periods. In sum a combination of heart humidity soil composition lack of or too much wind as well as seasonal, happening during the dormant or nearly dormant growth periods of summer . NO there is basically NO easy answer, NO one culprit. But the added effect of lack of growth being the lynch pin may add some light on this phenomena .
The reason for my change of opinion that humidity plays a big part in this has come about from this current season . We have had excessively hot humid sunny conditions EARLY in the season for about 10 days .. mid to upper 90′s and full sun and dew points in the upper 70′s and NO wind at all … stifling!! … yes it has been brutal . All of this mixed with heavy rains and one of the wettest springs on record and a late spring as well ( cold until late April) . Usually this hot sultry period arrives in July and August , most often mid to late July and early August , when the tree starts going into or is already in its dormant period of growth. Surprisingly during this odd season hardly any of my trees newly planted or potted or those established that are planted or potted have shown any sign of leaf burn or leaf tip burn.. Some have, but most haven’t . Even those that have burnt badly in past seasons or very young trees look pristine. What gives???
So I am now of the mind of adding the timing of the hottest period of the season and it’s effect or lack of effect ( depending on when it occurs) on the growth pattern of the tree (IE: dormant or semi dormant period) as co conspirators in this event, along with the other more obvious causes. Basically that growth periods/ dormancy and seasonal timing of such periods as effected by annual weather patterns plays at least some part in this. It would make some sense that conditions in certain parts of the country keep those dormant periods to a minimum or the dormant periods come in cooler or less humid or wetter times than others thus mitigating the burning of tree leaves.
I end this blog on leaf burn with my standard replies to those who constantly complain and are otherwise traumatized about leaf burn always looking for reasons, and cures for this common and likely unavoidable event. .
1. Yes you will likely have leaf burn on Jm’s
2. the more shade you give them the less you will have in general. keeping in mind that sun will color up your tree and shade generally will not.
3. leaf burn generally will become less as the tree ages
4. You may have less leaf burn in certain parts of the country but likely will have some
5. Don’t believe anyone who says they never have leaf burn … and offer then some $$ for some RX glasses
6. Try to keep any anal instincts you may have with your life to a minimum when it comes to Japanese maples. Perfection in nature is really only found in imperfection.
7. If leaf burn and other sources of imperfection in Japanese maples drive you nuts … dig up your JM’s and sell them to other less obsessed individuals. Then go to Ebay and buy a plastic one.. although be advised over time it too will likely fade or otherwise change from it’s current perfect plastic form .