December 29, 2012

1 - Old Christmas trees may be used as trellises for climbing beans and cucumbers in the garden.

2 - Conifer mulch is good for your garden.

Yard and Garden December 29, 2012

Q. #1

Each year after the holidays I take my Christmas tree to a municipal site that grinds them up to make mulch. I get some of the mulch for my garden and like that, but I was wondering if there was something else I could do with the old Christmas tree. Do you have suggestions?

A. #1

Making mulch from old Christmas trees is a great idea. The organic wood mulch along with needles and bark are a great covering over soils around trees, shrubs, and in flower beds. It helps conserve moisture and slowly adds organic matter to the soil as it decomposes.

However, you asked for other ideas. One to mention quickly is the old fashioned idea of burning. The twigs and needles are good kindling for starting fires in the fireplace and the larger parts of the trunk are good firewood. Just remember that wood ashes from the fireplace are not beneficial in Southwestern, arid land soils.

I have seen old Christmas trees (branches trimmed back or not) as trellises for growing beans. You may be able to grow cucumbers on them also, but you should probably brace the trees so that our winds will not blow the tree and vines over once the leaves of the vines have developed. At least be sure the base of the tree is well anchored into the ground or wires between regular fence posts hold the trees up against the wind. The trees will probably last for several years as trellises, so over the years you can collect several trees to make trellises. As they become too old and brittle to serve as trellises, they may be turned into mulch.

Q. #2

I am worried that mulch from Christmas trees is toxic to my plants. I have noticed that in the forest nothing grows under junipers, pines, and other conifers. Is there something toxic in conifers?

A. #2

No, they are not toxic. Shredded conifer trees make a great mulch for the very reason that things do not grow under them in the forest. Conifer wood and needles contain resins that shed water. This means that they do not absorb water and decompose rapidly. So they persist in their function as mulch for a longer period. In the forest that means they build up to greater thickness. The greater thickness blocks light that is needed for germination of seeds from many plants. Because the conifers are usually evergreen, they keep their needles throughout the year and shed water to the drip line very effectively. This creates a dry zone under the branches. Most plant seeds do not germinate in the dry soil under conifers. The result is a thick layer of mulch that decomposes very slowly under the tree creating a habitat that discourages germination of seedlings. However, you may also notice that new juniper and pine trees germinate and grow well in the natural mulch on the forest floor. Since you do not want weeds growing through the mulch in your garden, conifer mulch is good. It sheds water, allowing it to reach the roots of the mulched plants, decomposes slowly, smells good, and discourages weeds. It is a good mulch.

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:, office: 505-865-7340, ext. 113.


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