Fertilizing Mexican Elder and Nandina

I would like to know if I should fertilize my Mexican elder and nandina. I started the Mexican elder from a cutting and it has now grown to a height of almost six feet. At the onset I did give it some fertilizer, but none since. I tried another one some 20 feet away; however, it took three tries. Perhaps this one may have been overfertilized as the soil was hard. It has finally taken.

I am also growing some nandina. Do I fertilize these specimens or let nature take its course?

Since your Mexican elder trees are established and exhibiting growth, they will benefit from a little fertilizer each year in the fall after growth has stopped or in the spring after the leaves have formed. There is debate among some of the scientists as to which of these times is best. Either seems to work with most trees, but I tend to prefer the late spring fertilization time. Use a general fertilizer made for trees or lawns, but be sure it is not a lawn fertilizer with weed killer in it. If you use the fertilizer spikes made specifically for trees, be sure you stay quite a distance from the tree trunk when you place the spikes in the ground. They provide a concentrated fertilizer at that location and can damage roots and burn the tree if they are too close to the trunk. In a well established tree, place the spikes just outside the dripline of the tree. In any case, stay three to four feet away from the trunk. You can also spread granular fertilizer in a ring under and just outside the dripline. As with the tree fertilizer spikes, do not apply the fertilizer too close to the trunk of the trees.

The nandina will also benefit from light fertilization. The same rules apply as for the tree, but you can and should apply the fertilizer closer to the base of the plant since its roots do not extend as great a distance from the plant. However, too much fertilizer right at the base of the nandina plant can injure the plant.

Another general rule regarding fertilization of trees and shrubs is to stop fertilizing between the Fourth of July and the first frost. Fertilization after mid-summer may stimulate growth which will not have time to mature and will be injured by the first hard freeze.

The compacted soil you described around the second Mexican elder is probably the reason it was slow to establish. Hard, compacted soil makes root growth difficult for the tree and slows the establishment of the tree. This compacted soil sheds water and is difficult to keep moist enough. It also contains less oxygen which roots need for good growth. When planting trees, it is always wise to loosen the soil over a large area to encourage good root growth and rapid tree establishment. A mulch applied over the area of loosened soil helps the soil retain moisture and delays recompaction of the soil. It also keeps lawn mowers and weed eaters from damaging the trunk of the tree. Newly planted trees need little fertilizer except in very sandy soils which contain little in the way of nutrients for the tree. To determine the nutrient status of your soil, you can have your soil tested. Contact your local County Cooperative Extension Service for details regarding getting a soil test and understanding the results when the test is done.

Poinsettias and Christmas cacti

Is it time to begin making poinsettias and Christmas cacti bloom for the holidays?

Yes, we are approaching the autumnal equinox, the time when the sun crosses the equator and our days are twelve hours or less. From the plants point of view, the nights are twelve hours or more. It is this long night condition which prompts the poinsettia and Christmas cactus to begin forming their flower buds. Depending on the variety of poinsettia, it can take six to ten weeks of long nights to induce flowering, so late September is the time to begin the long night treatments.

You can do this in a number of ways. As long as there is no danger of frost or even temperatures approaching 40 degrees Fahrenheit, you can leave the plants outside where they are protected from street and porch lights. When it becomes necessary, bring them indoors to a room which is not used in the evening. Do not use lights in that room from sunset to sunrise. If there is a street light of porch light which shines into the window of that room, use dark curtains to exclude the light. You may also remove the poinsettia and Christmas cactus plants and place them in a dark closet each night, but remember to bring them back into the light each morning. Don't worry if you forget and leave them in the light a few times; this will delay the onset of flowering but not prevent it unless your forgetfulness becomes habit. It will also not harm them to forget and leave them in the closet for a day or two, but don't leave them there constantly. They need light to develop their flowers, just no more than ten to twelve hours each day. Continue to water them as they dry, but don't apply much fertilizer until after they have bloomed and growth resumes in the spring. Temperature also influences flower development. Cool temperatures near 60 degrees each night are ideal. Slightly warmer or cooler temperatures will not be a problem.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!