July 2, 2011

1 - Compost will help many New Mexico soil problems, but a soil test will also help determine solutions to problems.

Yard and Garden - July 2, 2011


Do you have any suggestions for compacted soil remedies? I have a big problem in my backyard and am not sure who to contact or what to do. I live in the Nob Hill area and have a western exposure for this part of the yard. I moved here in 1997 and the yard was barren and neglected. I immediately planted trees to give some shade, and although they have been slow to grow there now are a good sized Japanese scholar, Chinese pistache, two small vitex trees, and a desert willow that has been slow to grow. Almost everything I plant in back is stunted and seems to eventually die, except the trees. Anything more shallow rooted has a hard time. I am a Master Gardener so have some knowledge and the front yard is doing very well. I added compost and once, years ago, had the back rototilled. The problem seems to be getting worse. The most xeric plants just sit there and do nothing, except sunflowers and wild asters that love it there. I would appreciate any help you can give.

- Dianne P.



Since you are a Master Gardener I am sure you know about your local NMSU Extension Service office, but for other readers I want to remind them that the NMSU Extension staff is available to provide publications and personal information. Through your local NMSU Extension Service you can get publications explaining how to collect a soil sample and send it to a laboratory for analysis. The Extension Service staff can also help you interpret the results once you have received the results of your soil test. You have probably had your soil tested, but when a soil problem arises I recommend a new soil test. Look especially at the dissolved solids (salts), sodium, and organic matter levels in the soil. Other nutrients are also important, but from what you described these are important things to consider.

Organic matter helps modify the structure of soil to allow better infiltration of water and oxygen to plant roots. You added compost, but you may need to do this periodically since the compost oxidizes and diminishes over time.

Be careful which composts you use. Some have high levels of salts, especially those based on animal manures and biosolids from the municipal waste stream. High levels of sodium will "disperse" the soil particles making the soil very impermeable.

Some people recommend addition of gypsum, but that is beneficial only if the soil has high levels of sodium and the ability to drain well. Gypsum does not provide much benefit in poorly drained soils. Often a benefit seen when gypsum is added is the result of the rototilling used to apply the gypsum.

Rototilling or other means of opening the soil may be helpful, but because you have desirable trees in your backyard, you must take care not to damage the tree roots. Within 5 feet or so of the trees dripline, do not rototill. You can open that soil by piercing the soil with a spading fork and then "cracking" the soil by pulling back on the spade. Do not turn the soil as that would harm the tree roots. While rototilling or after opening the soil with the spading fork, apply a liberal quantity of good (low mineral salt content) compost.

The results of the soil test may also recommend addition of specific nutrients. Follow those directions when you receive the soil test results.

A final thought is that those plants that do well (sunflowers and native asters) should be used to maximum advantage. There are new sunflower cultivars you may want to try. There are new plant sizes and flower colors in these new sunflowers.

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.

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

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