A powerful arrangement for Mexican older trees (Sambucus mexicana), also called Mexican elderberry, is dependent on training the contour in planting and for the first couple of years of growth. After establishing the basic contour, just light pruning is needed to maintain the desired contour, especially if you would like to provide clearance beneath the drooping branches. These tiny trees grow in a naturally curved shape 10 to 30 feet tall and 25 to 35 feet wide. They are generally trained as multi-trunk specimens, but can be trained to one trunk.
Sterilize all pruning tools with denatured alcohol or a solution of diluted bleach mixed at a rate of 1 part bleach to 9 parts water prior to usage. Sterilization is particularly important after pruning diseased plants. Use a set of hand pruners to cut branches up to 1/2-inch thick, lopping shears for bigger branches up to 1-1/2 inches in diameter, and a pruning saw for additional bigger branches.
Eliminate any root suckers that grow from the base of the plant once they develop. These can be pulled off with your fingers if you get them early, otherwise, cut them off as much under the dirt as possible. This must be done when putting a brand new specimen and throughout the tree’s lifetime.
Pick the strongest, straightest trunk at planting time in spring and cut another trunks if you would like to train the Mexican elder as a single-trunk tree. The very best trunk is usually the middle most backward, but size and straightness ought to be factors in your selection. Should you would rather a multi-trunk specimen, keep just the three or four best trunks, removing any other straight back to the ground. When selecting trunks to get a multi-trunk tree, choose powerful stems while trying to maintain even spacing among them for balanced tree growth.
Drive a stake into the ground beside a single-trunk elderberry and attach it to the trunk with nylon webbing or polyethylene, building a figure-8 that loops around the tree, crosses over and loops around the stake. Staple the ends of the webbing to the stake to hold it in place. The figure-8 allows the tree to sway from the wind and develop strong roots. This step is optional, but helps train the trunk to grow as straight as you can.
Cut each of the trunks about two-thirds of the way up in the ground to trigger the growth of strong lateral branches. These branches will include the major structure for the tree canopy in after years. Make this cut immediately after planting the elderberry tree.
Select three or four powerful lateral branches from each trunk in spring from the second year of growth. Candidates must have strong angles with the vertical trunks — between 60 and 90 degrees — with balanced spacing around the trunks. Mexican elder trees possess a naturally drooping contour, so pick more upright branches above drooping branches if you would like clearance below the tree. Cut the extra branches back to their points of origin, just outside the branch collar in which the branch meets the trunk.
Trim back any tertiary branches with weak-angled crotches, that grow toward the middle of the tree, or even that rub or cross apart outward-growing branches. Do this in spring of this third year and in all following years. When you must remove one of two rubbing or crossing branches, pick the strongest of both, the division with the most powerful angles, or even the outward facing division.
Remove any dead, broken or diseased branches once you find them, cutting them back about 1/4-inch above a wholesome bud or division intersection. Pull off any water suckers that grow upright from branches, normally in the crotch where the branch meets the trunk or parent branch. Disinfect pruning tools after cutting diseased branches so you don’t spread the disease to healthy branches. This pruning action is necessary at all phases of a Mexican elder tree’s life and can be done at any time of year.
Clip long, drooping branches back to 1/4 inch above a bud to maintain clearance below the tree as needed. Branches can be left to droop nearly to the bottom, if needed, but drooping branches are often eliminated to shape a canopy with a rounded top and flat bottom.
