Mesquite's natural growth habit forms multiple trunks with low branches that shade the bark of the tree. Training mesquite as a yard tree means changing that efficient natural form in ways that don't harm the tree. Lifting the shape to provide walking space beneath the limbs and the look of a graceful tree rather than a rough thicket will take years. Improper trimming could introduce disease and cause stress damage.
Newly planted trees already have problems. Reduced root systems take up less water and need time to re-establish. Upper growth may partly die back if the water supply is irregular. Trimming limbs from a transplanted mesquite tree exposes bark to direct sunlight, which could dry out and kill the unprotected portion. Allow the trees to become established and show healthy growth before beginning the shaping process. This could take two or more years.
Desert mesquite should be pruned in summer when the upper portion of the tree actively grows. Sticky sap quickly seals pruning wounds and protects the wood from insects and fungal infection. Pruning during this growth period allows faster healing. In the desert, southwest storms come most frequently in the summer monsoon--pruning thick clusters of branches and thinning branch tips avoids most wind damage. Prune as early as May and as late as August.
Remove no more than 20 per cent of the tree's canopy in one season. Though this may seem like a lot, trees in more hospitable climates can be trimmed out by a third and still prosper from the new growth. In desert conditions, this much cutting can weaken the tree. Remove crossed branches and smaller trunks, encouraging the larger trunks of the mesquite to dominate. Leave some lower branches to shade the trunk until the tree shows enough canopy to prevent sunburn of the bark.
Sharpen pruning tools before trimming the mesquite. Sharp tools cut cleaner wounds that heal more quickly and are less open to infection. For small limbs a lopper works well. Larger limbs may be too tough for limb loppers even if they fit the jaws. Use a pruning saw instead, undercutting a third of the diameter of the branch and then cutting through from the top. Prune unwanted secondary limbs back to a half inch before the junction with the main limb. Prune larger limbs back to within an inch of the trunk. Don't cut so close that the bark of the main section is damaged.
Planted together, the natural shape of mesquite trees grows taller and opens up at low levels. The trees reach upward to compete for light and the canopy of the grove protects their bark from sunburn. Trees planted alone develop a lower growth pattern and require more pruning.