How long does a leaf need to photosynthesize to become energy neutral or positive

[duncanjer0]

I was wondering if anyone had any research to indicate approximately how long a leaf would need to photosynthesize to be energy neutral or positive to a tree. I moved to New Mexico a year ago, and for the past two years most of the Japanese Maples in my collection have had leaf burn by mid-summer. As a result, I don't really get any fall color, and the leaves basically burn and then fall off in the fall. I was thinking that since we have such a long growing season that extends into October and part of November, that maybe I could give a fertilizer boost in mid-August once the incessant heat abates and see if they would leaf out again. I don't want to do this though if it is an energy expense that the tree would not be able to recoup in a short two months of photosynthesis with a shortened photoperiod moving into fall. Any thoughts or recommendations?

 

[0soyoung]

It is a difficult question to answer definitively, BUT tossing on a bit of fertilizer is not going to trigger bud release..

 

[caffeinated]

Yeah, What osoyoung said, trees are biologically programmed to do what they do. You can trigger backbudding and growth by pruining since they naturally respond to that, but having extra nutrients available doesn't mean they ignore the seasonal clock. Leaves individually don't become energy positive or negative, the whole tree does. Leaves "harden off" when their cuticles form, but the extent of the heat they can take varies from species to species. Japanese maples in general don't do well in very hot climates, although there might be some cultivars that do better than others.

 

[dbonsaiw]

Yeah, What osoyoung said, trees are biologically programmed to do what they do.

Which makes a ton of sense as there is nothing down-regulating nitrogen, for example, in the ground as winter approaches. The tree simply uses the nutrients in the soil differently at different times of the year.

 

[WNC Bonsai]

You probably need to put up some shade cloth and get them out of the harsh sun, but they may not like the heat either.Good luck.

 

[Shibui]

After summer defoliation is used down here to get better autumn colour if leaves are summer burnt, exactly as you proposed. If a tree can be defoliated once in a year without affecting tree health (and most species can) it does not matter whether the defoliation is in spring, summer or late summer. Energy balance is a system wide thing rather than leaf to leaf.
The trouble I have found is finding the sweet spot for autumn defoliation. Too early and the new leaves burn, or worse, the trunk and branches get sunburnt. Too late and the leaves do not mature in time for the cool weather and don't change. One year I trimmed a bit late in summer. The maples grew new shoots but missed the deciduous cues and had leaves all winter (new leaves emerged in spring and returned to normal seasonal growth though)

 

[Mike Corazzi]

Maples belong in Vermont.

 

[Srt8madness]

Maples belong in Vermont.

Sez you. I have 4 in ground and one small one in a plastic pot rocking full (6hrs) sun through this insane heatwave. I'm constantly amazed that they are still plugging along. They've put on the long 2' shoots this year too.

Now the problem is touching the roots to get them in a pot. It is incredibly difficult for them to survive in a pot with a weakened root system through the heat.
Don't get me wrong, I'll never buy another JM for bonsai and wouldn't recommend them to anyone, but with the right care they can thrive.

 

[Gabler]

Maples belong in Vermont.

Tell that to the swamp maples in Florida. Acer rubrum is also one of the dominant canopy trees here along the fall line of the piedmont plateau in northern Delaware.

 

[Mike Corazzi]

Sez you. I have 4 in ground and one small one in a plastic pot rocking full (6hrs) sun through this insane heatwave. I'm constantly amazed that they are still plugging along. They've put on the long 2' shoots this year too.

Now the problem is touching the roots to get them in a pot. It is incredibly difficult for them to survive in a pot with a weakened root system through the heat.
Don't get me wrong, I'll never buy another JM for bonsai and wouldn't recommend them to anyone, but with the right care they can thrive.

Well, ground growing is CHEATING !! We are BONSAIists! We endeavor to force trees to comply with OUR conditions.!!!
Put em in the ground and it's cooler and they can use their mapley-brains to figger stuff out.
WE do the figgerin for em in pots.
And in HEAT
And WITHOUT LEAVES at times
And....face it. With nothing to bitch about, who would need a forum?