Is September a good time?
Late summer through early fall is a good planting time.
Here is a link with growing information.
https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/weeping-cherry-growing-tips.htm
I noted your advice about not trimming but I like the weeping branches about l/2 way down the trunk. Mine are almost down to the ground. Would I damage the tree if I trimmed them just a little to a shorter length?
You can prune the long branches to within 6 inches of the ground. If you prune any shorter you jeopardize the weeping growth of the Weeping Cherry Tree.
https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/pruning-weeping-cherry.htm
The knarl on our tree has sap coming out of it. What do we do?
This is likely a canker.
Here is a link with more information.
https://www.gardeningknowhow.com/plant-problems/disease/weeping-amber-in-trees.htm
I have a weeping cherry blossom tree (1 yr) and I used too much weed killer around it and it is dying and most of the leaves are curling. I put weed and feed and Bayer tree and root for bugs and fertilizer, and water it well every other day, as it has not rained here in Philadelphia in 2 wks.
Watering well to try to remove the residual chemicals from the soil is the best you can do.
It is likely the tree will not survive.
Here is a link with more information.
https://www.gardeningknowhow.com/plant-problems/environmental/herbicide-plant-damage.htm
If I am going to heel in my weeping cherry for winter, should I trim the branches? The tree is about 1'6" tall, but the limbs are about 2' long.
This article should help: https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/pruning-weeping-cherry.htm
We have a weeping cherry tree recently planted and now starting to produce leaves and blossoms; however, there are also some growths taking place on the trunk. Can you please advise if these should be removed and, if so, when and what is the best method of removal so as not to hurt the tree?
Yes, prune away the suckers as soon as they appear. They are growing from the root stock and will take energy away from the tree.
https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/weeping-cherry-growing-tips.htm
We have 10-year-old pink-flowered grafted weeping cherry. The top branches were never pruned, so they are growing straight up, but the bottom branches are weeping. So basically, two tree varieties are growing from the existing trunk. Is it far too late to crop the straight up branches from the top? I am guessing "yes" since the upward branches comprise the majority of the tree. Perhaps pruning the minimal weeping branches is the best advice at this point? Other than the bizarre shaping, the tree appears healthy and the entire tree flowers in the spring. Thanks for any input.
You can try to thin out the top of tree with some pruning to visually make the tree more appealing.
Here are some links for you.
https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/pruning-weeping-cherry.htm
https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/weeping-cherry-growing-tips.htm