Although they're under shade cloth, my Japanese maple seedlings are still getting scorched.

[Toshi]

They get morning sun from about 830 - 1 and then shade the rest of the day on my south facing balcony. I thought the cloth would help but they're still getting roasted like a washed up celebrity on comedy central.

This is the screen that i bought - https://a.co/d/016ALaw

I guess it's not suitable for this purpose? I'm not really sure what to do, the foliage is constantly scorched both at the apex as well as the base.

 

[ShadyStump]

I'm no expert on maples by a long shot, so grain of salt.

What's the weather been like? Any way of raising the humidity?
When I look at the soil I see little green bits. Is that fertilizer? If so, tell us about it, because it's possible they're getting too much and that's what's burning the foliage.

 

[Dav4]

My best guess is that the roots are staying too wet +/- fungal issues with the foliage... and overwatering and underwatering issues often look surprisingly simple. Fwiw, I'm pretty sure lack of humidity isn't the problem... I've been to NYC in July!

 

[Bonsai Nut]

Looks to me like too hot and dry. The leaves are crisping. In the heat of the summer, I would recommend keeping green Japanese maples away from ANY direct sun. Additionally, I would protect from the wind and consider misters if it is going to be really hot.

Down here we have plenty of humidity, but even my landscape red Japanese maples are looking a little toasted as we start to get up in the 90's. You can water all day long, but if the leaves are drying faster than the vascular network of the tree can provide water, the leaves are going to scorch. Damage will start with upper / outer leaves first, with lower and inner leaves avoiding damage initially.

Also, if the leaves of the tree are touching that black shade cloth in the heat of the day, you may get physical burning as well.

 

[morriganflora]

Scorch issues are just too much transpiration for the roots to keep up supplying water to the foliage. If you haven't got root damage it's either wind, low humidity, minerals in the wind (usually only a problem right next to the ocean), or too much heat. With a shade cloth up on a balcony I'd say it's a hot wind causing scorch. Misting foliage will help if you're confident you're watering enough or suspect root damage. Otherwise, more water. Preferrably cold.

 

[Toshi]

I'm no expert on maples by a long shot, so grain of salt.

What's the weather been like? Any way of raising the humidity?
When I look at the soil I see little green bits. Is that fertilizer? If so, tell us about it, because it's possible they're getting too much and that's what's burning the foliage.

Weather has been miserable, insanely humid, temps on the ground as high as 120 some days.

I applied small doses of controlled release fertilizer 13 13 13.

 

[Toshi]

My best guess is that the roots are staying too wet +/- fungal issues with the foliage... and overwatering and underwatering issues often look surprisingly simple. Fwiw, I'm pretty sure lack of humidity isn't the problem... I've been to NYC in July!

Definitely possible, the substrate they're in is a bit heavy and I'm watering every 4 days or so.

 

[Toshi]

Looks to me like too hot and dry. The leaves are crisping. In the heat of the summer, I would recommend keeping green Japanese maples away from ANY direct sun. Additionally, I would protect from the wind and consider misters if it is going to be really hot.

Down here we have plenty of humidity, but even my landscape red Japanese maples are looking a little toasted as we start to get up in the 90's. You can water all day long, but if the leaves are drying faster than the vascular network of the tree can provide water, the leaves are going to scorch. Damage will start with upper / outer leaves first, with lower and inner leaves avoiding damage initially.

Also, if the leaves of the tree are touching that black shade cloth in the heat of the day, you may get physical burning as well.

I haven't been misting them lately. I can't remember where I read it but a source online said not to as water staying on the leaves will cause them to burn : l

I think I'll try to move them to a position that's completely shaded.

 

[Toshi]

Scorch issues are just too much transpiration for the roots to keep up supplying water to the foliage. If you haven't got root damage it's either wind, low humidity, minerals in the wind (usually only a problem right next to the ocean), or too much heat. With a shade cloth up on a balcony I'd say it's a hot wind causing scorch. Misting foliage will help if you're confident you're watering enough or suspect root damage. Otherwise, more water. Preferrably cold.

Misting I haven't been doing but I'll start, thanks.

 

[Paradox]

The soil in your first picture looks dry to me.

I am out on Long Island where its a bit cooler than NYC. I've been watering my maples twice a day. They get about the same amount of sun as yours, maybe an hour less per day. I don't use a shade cloth but mine are in my yard. The concrete and pavement in the city can radiate a lot of heat

 

[Glaucus]

Maybe the shade cloth itself also gets hot? They are quite close up the it. If the leaves tocuh, they can get burned. Especially because yours is black.
That will of course be localized to only those leaves.

 

[Mikecheck123]

I'm watering every 4 days or so

 

[ShadyStump]

Weather has been miserable, insanely humid, temps on the ground as high as 120 some days.

I applied small doses of controlled release fertilizer 13 13 13.

Everyone else so far is more knowledgeable than me, but I'll give you a tip on the slow release fertilizer: find some of those tea bags for loose leaf tea, and put your fertilizer in that and just lay it on top of the soil. That way you can remove it if you need to.
The release rate on that stuff can be very unpredictable, but it happens allot faster when it's hot and humid. Watering more may help keep any excess flushed out for now, and that's what people are recommending anyway.

 

[Paradox]

I'm watering every 4 days or so.

In this heat....... probably not enough

Do yourself a favor, get some wooden chopsticks or pieces of small dowels and stick them in the pots as deep as you can.

Leave them in there.

Every day, pull them put and look at them.
Water the trees when they are almost dry.
Do not wait until they are fully dry.

 

[morriganflora]

a source online said not to as water staying on the leaves will cause them to burn : l

If that were true you'd see burns in little pock marks where ever the water droplets were in the few minutes before they evaporated. It's excess transpiration that causes scorch, not light exposure. This is simply a myth.

 

[Glaucus]

I haven't been misting them lately. I can't remember where I read it but a source online said not to as water staying on the leaves will cause them to burn : l

I think I'll try to move them to a position that's completely shaded.

Common myth. Doesn't make sense from a biology point of view nor from an optics point of view.
From biology, it doesn't make sense that rain and sun burn leaves, because it happens all the time. And all leaves would have to get tougher.
You just don't observe this type of damage.
From the optics, you'd need a droplet of a certain size and with a high contact angle to actually focus the light properly.
Not impossible, but it is a special case of droplet. Theoretically, they can exist. But their existence has not been demonstrated, nor their effect on the leaf.

I do wonder though about watering with very cold water when the soil, roots, leaves are all pretty hot.
Of course, you need to avoid the hot water that will be in your hose when you start watering.
That water can get super super hot. Always check the temp with your hand before you water the plants.

 

[Mikecheck123]

Common myth. Doesn't make sense from a biology point of view nor from an optics point of view.
From biology, it doesn't make sense that rain and sun burn leaves, because it happens all the time. And all leaves would have to get tougher.
You just don't observe this type of damage.
From the optics, you'd need a droplet of a certain size and with a high contact angle to actually focus the light properly.
Not impossible, but it is a special case of droplet. Theoretically, they can exist. But their existence has not been demonstrated, nor their effect on the leaf.

I do wonder though about watering with very cold water when the soil, roots, leaves are all pretty hot.

Not to mention the fact that all forests would be decimated whenever it rained.

 

[Bonsai Nut]

a source online said not to as water staying on the leaves will cause them to burn

Some weird wives' tale that originated god knows where. The idea was that water droplets on leaves formed mini magnifying glasses and the sun rays would burn leaves.

I guess no one stopped to question "so why don't all the trees burn up when it rains during the day... all over the world... regularly?"

FWIW I have watered my trees in SoCal heat as hot as 107 F, full sun and low humidity, wetting all the foliage, and have never seen anything bad come of it. In fact today in NC at 92 with a decent wind, I was more focused on wetting foliage than watering the soil. When it is super hot it is actually easy to overwater the soil. The roots can only take up water so fast. Meanwhile the foliage is getting scorched. Solution: water the foliage.

 

[Deep Sea Diver]

The issue we see during with leaves drying etc often are not caused by a single thing…it’s multiple causes. Yours is a good example. Dry media, high heat and uncontrolled fertilizer. ….So it looks like it’s just this one thing, but it’s actually the confluence of events, sometimes including things one does a couple weeks ago.

So… Yep… watering foliage and just watering frequently so the leaves can dry before dark.

If you have decent well draining media there shouldn’t be much fear of overwatering.

Personally I have my maples in shade after 10am through 4pm or later, especially during >90F days.

Also absolutely do not recommend having fertilizer pellets on in the heat, especially in a way that one can’t take these off easily. We use tea bags with Osmocote Plus and remove these in the heat as @ShadyStump recommended. One needs absolute control of this variable during heat spells.

Cheers
DSD sends

PS @morriganflora. Welcome Aboard! Also can you please enter your approximate location and USDA zone. It will be very useful to all when you are receiving and giving help.

 

[Toshi]

In this heat....... probably not enough

Do yourself a favor, get some wooden chopsticks or pieces of small dowels and stick them in the pots as deep as you can.

Leave them in there.

Every day, pull them put and look at them.
Water the trees when they are almost dry.
Do not wait until they are fully dry.

The soil stays wet for a long period of time. I put my finger in the soil as a test. One of the seedlings is in a faster draining soil and that one dries out every other day.

All my other plants I have to water daily it's only these that are in a heavier mix.