Give young tree roots some space
One of the best favors you can do for a young tree is to provide a grass and weed-free area around the trunk. This circle not only reduces competition for water and fertilizer, so the tree grows faster, but it also protects it from damage by mowers and line trimmers. Line trimmers are the number one cause of stunting and death of young trees.
Grass and other plants with roots near the surface are fierce competitors for water and nutrients. Not only do the grass roots get first chance at water and fertilizer, but grasses actually produce a substance which suppresses growth of competing roots.
I planted two apple trees one spring at the very same time as a neighbor across the fence was planting apple trees. He remarked that the trees looked the same now, but mine would probably grow faster because I had a “green thumb”. Two years later, when my trees were indeed twice the size of his he said, “You really do have a green thumb. What is your secret?”
I pointed to the ground around his tree trunks. Grass was growing right up to the trunk, but it was neatly trimmed with a line trimmer. Then I pointed to the 4 foot diameter circle of mulched soil around my trees. I pointed to the nice healthy bark on my trees and compared it to the nicks and cuts on the bark of his trees. I explained to him that the food made by the tree leaves travels to the roots in tubes just under the bark surface. When you cut through the bark, you disrupt the flow of food to the roots. A smaller root system means that tree branches grow more slowly also. I see trees which have been constricted near the soil line so badly that they will never recover. If the bark is cut off all the way around the trunk, the tree will die.
You can put metal, redwood or plastic edging around the circle to keep the grass from growing into the circle. I prefer not to use concrete edging because the size of the circle needs to expand as the tree grows. You can cover the soil in the circle around the tree with weed barrier fabric. It shuts out the light to the soil below, and no plants will grow without light. You will probably cover the fabric with bark or some other attractive mulch. Eventually, the bark will break down and some weed seeds will blow in and sprout on top of the fabric. They are usually quite easy to remove. Two or three inches of bark alone, without the weed barrier fabric, will eliminate 90% of new weed growth, unless grass is allowed to grow into it.
Mulch also reduces evaporation of water from the soil, which reduces the amount of irrigation water needed.