Red Maples do not normally grow here in zone 3, but I brought one back from my son's yard in B.C. It comes back every year from its roots, but it is always a red colour. I keep it as an interesting ground cover plant.
Caroline Calgary zone 3

It doesn't look like chlorosis to me, but I don't have much experience with trees - just perennials.

Whatever it is, your tree is stressed. A few thoughts come to mind:

If it was not chlorotic when you bought it, 6 days is pretty soon after transplanting for chlorosis. It's not impossibly soon, but it does raise an eyebrow here. My guess is that the tree was already heavily stressed when you bought it. It is possible that they did not adequately fertilize or water the tree while it was in their care (happen all the time). It sounds like it was badly potbound.

One of the contributing causes to chlorosis or other stress is waterlogged roots. The way you describe planting your tree is a graranteed way to waterlog the roots. I know you were probably told to do it this way by the nursery - but many nursery staff are only passing on old outdated info.

When you dig a hole in heavy clay, then fill it with loose airy soil, and you water (or it rains), the water will stay in the loose airy soil, not drain into the heavier, dense clay. (this is not necessarily the cause of your tree's stress, but it will be contributing to it.)

Holes shouls generally be *much* wider than deep. One of the big mistakes people make is planting too deep.

30 degrees is awfully hot to be transplanting a tree. And you exposed the roots to air for several hours...

2" of mulch is on the light side for a newly planted tree. I would have suggested 3-4" at a minimum, being careful not to put it up against the trunk.

Check with the nursery as to what their return policy is. Your tree may make it, but if the nursery has a short guarantee time, you may want to take it back and buy from a different place.

Thanks for the responses. Indeed we have had some heavy rains in Ottawa for the past few days. The tree has been probably swimming in the clay pit.

The garden center was quite helpful - they did tell me to mix the clay with the new soil. I did a 50-50 mixing.

The tree leaves looked fine (the stems were slightly lighter green than the rest) in the nursery, although they were not as dark-green as some other October Glories we saw in other nurseries. We picked this particular tree as we liked the yellow color (before knowing it probably means iron deficient). There weren't a lot of leaves on the lower branches probably due to close packing.

Is there any way to reduce the stress of this tree?
How about I find a cool morning/early evening to:

(1) Replant & raise the base of the hole so the tree's trunk base is about 3" above ground.
(2) Refill the hole with 50% clay and 50% black/garden soil, mixing with appropriate amount of granular sulfur to lower the pH to avoid future chlorosis.
(3) Cover with grass-clippings and 4" of mulch.

Thanks a lot.

Just a few rule of thumb I practice when I am about to transplant a large shrub or tree. One is to prepare the hole ahead of transplanting. Second, to water the plant well and several hours before transplanting. Third, not to transplant in high sun or during a very hot day. And when transplanting, it has to be done quick. Like I'm not waiting 30 minutes to cover the roots. Another thing, When the tree is in the hole and backfilled halfway, I would water it then just to get rid of air pockets. Air pockets are deadly in winter. Then I back fill all the way to the top. Have you observed trees in nurseries? Their roots are often burlapped and topped with mulch to keep their roots unexposed and moist. It's very important to not distress the roots as much as possible.
I suspect your plant is undergoing transplant shock. It's roots were exposed and stressed over several hours during very hot weather. Do not fertilize. It would burn the plant. It may have been doing poorly in it's pot before transplanting. Just continue to keep the plant moist but not overwatered. Do not transplant it again. It's been through a lot. It the leaves are stressed, let it be. It will recover. Just make sure it survives winter and it should be okay by next season.

I'm not sure if there is a problem with drainage? Did you observe the tree drowning in water? If so, the simplest way to protect it is to add a thick layer of mulch so the water is channelled away from the base. (Do remember to remove the mulch next season). You may try to address any drainage issue by improving the soil in the perimetre of the pit. For example, in my yard, I employed the double digging method to amend my clay yard with compost. Hard work but the results were instantaneous.

Thanks for the great tips.

My yard is slightly graded, and with the cedar mulch raising the tree perimeter, there was no standing water around the tree's base even after overnight heavy rain.

I will bury compost in the perimeter. I suppose the thick mulch also protects the root from freezing. But may I ask why should I remove it next spring?

Mulch has multifunctional purposes. In winter it serves to keep temperatures steady and protects against the freeze and thaw cyles.

In spring, they need to removed from the base because mulch also harbours insects, disease and other creatures that can damage a tree starting from the base of it's trunk. The use of cedar mulch helps tone down the insect population.

Mulch can also be used to prevent emerging weeds so are used in garden beds but bear in mind to give space at the base of plants.

Mulch can also protect plants in the height of summer weather when conditions resemble drought - so it conserves water.

And as you can see, mulch if heaped to a certain degree can act like a roof thatch and have rain slide off the base of the plant.
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I don't think your plant is drowning in it's hole - based on what you have said - so no worries about that.

Thanks.

One more question:

From checking online resources I realized that the container-bound roots might have choked the red maple tree. Its leaves are smaller than the other October Glories maples we saw, and there weren't many of them on the branches. The pot-shaped roots actually found/made a large crack in the pot and grew out of it.

I wonder whether I will have to cut the encircling roots at some point. Now I know hot summer is a bad time for tree surgeries. How about next spring when the tree is still dormant?

In cases of root bound plants, I normally would pry the roots loose and that's about it. I don't do root pruning unless I am planning to repot the plant.

This is a small plant and so for now let it rest. You can probably rectify the problem this Oct when the plant goes dormant. - and all you need to do is to dig out a large root ball, pry the outside roots gently with a stick and replant it. make sure you remove any possibilities of air pockets because as I said, these can kill plants during winter.

Here is a follow-up development:

While I suspected the tree suffered from chlorosis from the alkaline heavy clay, I bought a can of iron-chelate and experimented it on one of the branches. I dissolve a few grams of iron-chelate powder into about 2L of water. Then I dipped all leaves in the "experiment branch" in this diluted iron-chelate solution. I then dumped the iron solution right onto the root ball.

After 3 days of the treatment, I noticed that the dipped leaves appeared much greener than the rest of the tree, which hasn't improved (or got worse).

So I still suspect cholorsis in play with the red maple tree. I am going to dip more leaves to see if there is any good improvement.

By the way - against all wise advises we still decided to replant the tree in order to:

(1) Raise the tree bed to improve drainage
(2) Cut the circling roots
(3) Most importantly, remove the sod that I, due to lack of experience, burried at the bottom of the planting hole.

At the time of exvacation, the root ball was swimming in a large pit due to poor drainage (not visible from the surface). The smell was awful (guess this is what CSI calls "decomp"). We removed all of the decomp mud, washed the tree's roots, and cut off the roots that have been affected by the rot. We also cut off the encircling roots.

We then widened the planting hole from 2.5' to 3.5', filled it with fresh black earth & clay (30-70 mix). We elevated the root ball to be about ~6" above the ground surface. We compacted the mound to make sure there wasn't large air pockets. Then we covered it with ~4" of red cedar mulch, leaving about 6" of space around the trunk. It looks like a large red donut circling the tree.

Hopefully the tree will recover from the surgery.

well, let's hope for the best. The rotting smell probably came from the rotting grass you place din the hole.

Some updates:

(1) A week ago we dipped more leaves in the iron-chelate solution. But they did not turn greener than the rest.

(2) The leaves turned even redder after our replant. We thought the tree was going into hibernation after our recent abuses, but just today the tree actually became greener! We also noticed the tree growing some new small green leaves. We also noticed that the leaves that are shaded by others leaves were significantly greener.

The only thing that we did differently was the application of some 20-7-7 fertilizer on the surface of the mulch about 1.5 ft away from the tree's trunk. After watering, the fertilizer dissolved and sipped into the roots' surrounding soil. Maybe the tree really likes the boost and has decided to utilize the rest of the summer. Ottawa is experiencing a record-breaking heat wave these days. So the tree may be encouraged to produce more chlorophyll, but the steaming sun still keeps the surface leaves red.