To control weeds and reduce moisture loss from the soil during hot, dry periods, spread a layer of organic mulch 2 or 3 inches thick on the soil under the poplar tree.
Poplars grow best when they have a good water supply and soil that drains well. Water newly planted trees regularly for several weeks until they are established. Otherwise, during periods of normal rainfall it is not necessary to supplement their water. While they are able to manage considerable drought in fields out in the wild, it is beneficial to water those poplars in the yard when rainfall is scarce.
Poplars are heavy feeders, tending to monopolize the nutrients in the soil at the expense of nearby turf or ornamental plantings. Each fall sprinkle fertilizer on the soil under the tree out to 1 1/2 times the distance from the trunk to the tips of its branches (the drip line). If the distance is 10 feet, fertilize out to 15 feet from the trunk. Do not allow the fertilizer touch the foliage or trunk. Use 1/2 pound of fertilizer for poplars with a trunk diameter of 1/2 inch at the base. For larger trees, use 1 pound for each inch of trunk diameter. Do not apply fertilizer when planting a tree, nor during the first season.
Train young Poplar trees to develop a single trunk, or central leader, by pruning lower, secondary large stems. While it is not necessary to prune poplars routinely, it will be necessary to remove dead and broken wood branches from time to time, especially as the tree ages. This tree is notable for producing pesky root suckers that, unless removed, will grow into full trees. Prune when the tree is dormant, not later than January, because pruning wounds will bleed if sap is rising.