Planting new trees

Having read some of the articles on Hugelkultur, I was wondering weather it would be beneficial to place a short poplar log on the edge of the tree planting hole to help absorb water to help the young tree during the warmer summer months until it gets established?

Howdy Richard, welcome to permies.
I am trying to get a clear picture of what you are asking.
So you have a hugel bed?
You will be planting new trees into the hugel?
When you plant the tree you are thinking of adding a poplar log in the same hole because it will sponge up water and then give up the water to the young tree when needed?

Richard - if you are talking about establishing a new tree in an area that is NOT already a heuglebed and burying some wood with the planting to act as a sponge, etc. Remember that in the first year of establishing any type of heugle the "sponge effect" works in reverse. Meaning - the log you bury could take moisture away from your young tree and would certainly tie up some nitrogen that your tree needs to get off to a good start. A lot would depend on your soil, your rainfall and climatic factors but I would use caution trying to get the beneficial effects of a mature heugle from a single log in the first year of burying. JMHO

I do not have good experiences planting trees on huegelbeds. One died and the others are growing far slower than those I have planted the traditional way.

Thanks for the tip. It seemed like a good idea at the time. I guess I'll just have to keep them watered well if we don't get plenty of rain.

On a related, but different, note - the Bullock brothers plant a nitrogen fixing shrub along with their young trees, nearby or even in the same hole. It won't help with keeping the tree watered, but reportedly is a real help in providing nitrogen for the young tree as it is getting started.

Planting trees on/in hugelbeds is not recommended, but that wasn't what I understood the OP to be asking about.

Peter - good point about the N+ fixers. I do this too when I plant new fruit or nut trees primarily using moringa as a nurse tree and to provide some supplemental N+. I usually include a couple of comfrey crowns, some alliums and some marigolds as well to bring in pollinators, repel harmful critters and mine some deep nutrients. I've not come up with a specific guild for specific trees yet but this basic guild has been working well to get the new ones started.

Additionally, as I protect the new plantings with a cage of field fence (to keep deer and rabbits at bay) I plant my sugar snap peas around the base of this cage and they use it as their trellis when they grow. These legumes also provide a little N+ to everyone and protect the young trees from sun scald (and taste pretty good to boot). YMMV