Issue: May 12, 1997

Fertilize newly planted trees?

I live in Ruidoso. In late December 1996, I planted ten dwarf Alberta spruce; in April 1997, I planted ten green mound junipers, and then seven mugo pines. All the plants are very small, but I used no fertilizer when I planted them. They are looking good now, but I wonder when I should begin fertilizing them. Also, what type of fertilizer should I use? I have them surrounded with pine bark to prevent water loss. I want to xeriscape my new home at this 7000 ft. elevation.

Regarding fertilization of newly planted trees -- don't! For at least the first year, their nutrient needs will be minimal. During this time they are establishing their root systems, and fertilizer (especially nitrogen which stimulates stems and leaves) will not be appropriate. You may begin a light fertilization a year from now as the leaves are forming, but for this year, be patient.

The type of fertilizer is not especially critical. You can purchase fertilizers which are specially formulated for trees, or you can use a general purpose fertilizer. Just be certain that the fertilizer is not a "weed-and-feed" product containing a postemergence herbicide which could harm the trees.

When applying the fertilizer around the tree, don't put it too close to the trunk and be certain not to put it all in one spot - it can burn the tree if too much salt is absorbed by the roots. General purpose fertilizers contain nitrogen, phosphorus, potassium, and in some cases trace nutrients. Nitrogen is needed for growth of stems and leaves. Phosphorus is needed for good plant health and energy in the plant. It stimulates flowering and fruit development, not your main purpose in growing pines, juniper, and spruce. The potassium is needed for good root development and plant health. Trace nutrients are used in very low concentrations but are sometimes a limiting factor in plant growth in New Mexico. The nutrient the trees will need most is nitrogen; however, they also need the others.

It would be wise to take a soil sample to determine what your soil needs to support good tree growth. Your local County Extension Service can advise you as to the proper method to collect the sample and tell you where you can get the soil tested. They can also help you understand the results of the soil test if you need help.

As to the xeriscape, you are off to a good start. Some people who live at lower elevations in New Mexico may question the mugo pines and dwarf Alberta spruce, but at your elevation they are appropriate if irrigated properly. The spruce will need more irrigation than the pines, but the needs of each species can be supplied with a properly designed irrigation system. The use of mulch is also a good idea, especially when starting trees as it not only reduces evaporation of water from the soil, it keeps grass from competing with the developing root system of the trees, and it keeps lawn mowers and weed whackers away from the tender bark of the young trees.

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!