Brown tips on Japanese maple leaves

[Saeven]

Hi Everyone.

Am looking for help with a small Japanese maple I bought at a local bonsai store here in Canada. It's potted in Akadama and seems very young; it's probably 8-9 inches tall.

The problem: When it sprouts new leaves, their tips turn brown.

I've been keeping it indoors near a south-facing window because we've got an infestation of Japanese Beetles outside - between them and the weather I fear it wouldn't live long at all.

Any advice? Help appreciated!

 

[0soyoung]

meh. It is common this time of year. Most commonly I find it results from having waited too long to water a week or two before I first see it. It can also happen because of wind/sun and overwatering.

Not to worry, IMHO.

BTW, your tree will be better off outdoors.
Even if the beetles ate all the leaves, it will usually produce another flush (2 o3 3 per season), though it might not this year as it is a bit late in the season for it.

 

[Saeven]

Thanks for the kind response. I'm still a student!

I've read (maybe too much) that the Japanese maples can often crisp up in direct sunlight. Should I try to control how much light they get per day? I'm game to move it outside.

 

[0soyoung]

Being inside, even in a sunny window, the leaves are shade adapted which means they will be 'overloaded' in full bright sunlight. Most varieties, even red leafed ones, respond by producing anthocyanins that literally shade the photocenters (chlorophyll) and give the leaves a reddish tint. More sun, plus a little breeze will often cause the leaf burn (flame out) you've read about.

So, when you put it outside, it should have speckled to full shade at mid-day when the sunlight is most intense. Keep your eye on the leaf color and give it more shade if the leaves darken markedly. Next year you'll be able to give it more sun without as much trouble, because the new leaves are much more adaptable.

btw, in a pot the roots will need more protection from cold than one planted in the ground, but I suspect you'll be bringing this one into a winter storage location not long after leaf drop. Storage temperatures ought to stay between 15F/-10C and 40F/5C. Warmer and it might not get the dormancy it needs to stay healthy. Colder may damage the roots and could even kill the tree outright. You also may need to water if the substrate doesn't remain frozen.
On the other hand, if you happen to have a cold hardy variety that could be planted, you'll just need to toss mulch/hay (say) over the pot.