I assume you are somewhere in New England, but where makes a difference. In MA and other more southerly parts of New England, there is an insect, the wooly adelgid, which will slowly kill hemlocks without pesticides. So if you are in an area that has adelgid, it might not be worth trying to save since it will likely be killed when adelgids arrive in your area. So far they haven’t been seen in my area of central NH, and we have a lot of hemlocks.

This was a tough summer for transplanting due to the heat. What kind of precipitation did you have during that time? Is the hemlock growing in a spot with any shade, or did you provide any temporary shade during hot parts of the day? Hemlocks will tolerate sun in northern New England, but they naturally grow in shady areas and when in a sunny spot along with heat and the recent root disturbance, they will show stress. Whether yours will recover or not I don’t know since here are too many unknowns, but maintaining best possible care until the ground freezes will give it the best possible chance.

- Providing it with some shade during any coming hot weather may help, such as a sheet or tarp rigged on poles set to the southwest of the plant, or a pop up shelter erected over it.

- Actually check soil moisture In the area where the tree’s roots currently are by sticking fingers down into the soil. Having a drip line is only half the story. You have to water long and slowly so that the water has a chance to soak down deep enough to moisten the entire root zone to depth. Then don’t water again until the soil a few inches down is approaching dry, but don’t let it dry out. Often folks will water daily with a soaker for a matter of minutes and assume that this is enough, which in most cases of new plantings, it isn’t. In my garde with my water pressure and equipment, it took several hours to soak the soil down a foot or more You will want to check to see how long watering has to continue in your garden and with your equipment. Continue watering when the soil feels like it needs it right up until hard freeze.

- Don’t fertilize. It is already stressed and won’t be able to use the fertilizer. I rarely fertilize woody plants because my soil is adequate for their needs. Do a soil test if you are wondering about your soil to see if anything is needed.

- Mulch well in the tree’s root zone if you haven’t, though leave the mulch a few inches away from the trunk, not against the bark.

After that it is mostly a matter of patience. You most likely won’t have a feel for the survival of the tree until some time well into the next growing season, though with the number of bare branches, I don’t hold out too much hope. Hemlocks will grow to be quite large trees, and though I can’t be certain from the photo if there is actually room, it looks like it may outgrow the allotted space. This time last year we had to take down a windrow of hemlocks planted 20 years ago as less than 2 foot saplings because they were something like 20’ wide and at least that tall. So keep that in mind as well. There are some lovely, slower-growing, hardy evergreen conifers that might work better In the long run if your hemlock doesn’t work out.

I have a hemlock that died last year. It was the 20 foot tall sort. I've talked to a state horticulturist and some tree guys. It needs a sample drilled and examined in the lab because it was not infested with wooly adelgid or hemlock scale, as far as we can tell.

Woolly Adelgid is in Southern Maine. They look like little bits of cotton on the underside of fresh shoots. Maine also has Hemlock scale, which is on the underside of older shoots. You might need a magnifying glass to see it. I presume something freshly planted won't have pests, but looking at the underside of new and older growth with a magnifying glass is an easy check.

The horticulturalist described it as a one-two punch, with the adelgid killing the new growth, the scale the old growth.