October 8, 2011

1 - Soil and weather conditions could have contributed to poor tomato production this year.

Yard and Garden - October 8, 2011


I live in La Luz, NM. and have some questions about my tomato plants. This year I have plenty of foliage but the fruit is very small and sparse. I wonder what is wrong and what I can do to help get a better crop next year...I have done all the usual things I have done in the past - I used composted manure and Miracle Grow ™.

- Karl D.


The usual answer to your problem (lush foliage but poor or no fruit production) is that the plants received too much nitrogen. Manure and commercial fertilizers often provide high levels of nitrogen which results in excessive vegetative growth at the expense of flower and fruit production. Early application of nitrogen is helpful in establishing large plants that can bear large crops, but as the plants enlarge, they need more phosphorus (from balanced fertilizers, phosphate fertilizer, or some organic sources such as colloidal phosphate rock). Phosphate is not readily soluble in most New Mexico soils and water, so it is more difficult to apply to plants. It must be incorporated into the soil to put it next to the roots if applied after planting. If you apply phosphate before planting it can be worked into the soil (incorporated) at that time. Some organic phosphate fertilizers such as bone meal and others do not release the phosphorus to the plants in our highly calcareous soils (such as is common in La Luz and many parts of New Mexico. The cause of this problem is the high pH (alkalinity) of the soil that prevents phosphorus and some other nutrients from dissolving. Plants cannot absorb minerals that are not dissolved in water. Organic matter in the soil should help acidify the soil and increase the availability of phosphorus. The manure you applied should have helped with this. Unfortunately, some manures (even composted manures) have high levels of mineral salts and calcium resulting in a high pH that can continue or increase the problem. Now is a good time to submit your soil to a soil testing laboratory to determine the nutrient, soluble salt, and pH status of your soil before you plant next year. Your local NMSU County Extension Service agent can provide information about soil testing and understanding soil test results. The discussion above is the standard answer to this question. However, I received similar questions from many people this year and have delayed answering because I think the weather this year was a major contributing factor. Cool, dry weather well into late spring, followed by heat, wind, and drought made gardening very difficult. In addition to soil factors, there are other things to consider as well. When you plant early while temperatures are still cold, a clear plastic mulch to help warm the soil and protective coverings on cold, windy days and nights will help the plants establish before the heat impacts their growth. (Clear plastic is more effective for warming the soil than black plastic.) Plant cover or organic mulch over the plastic mulch later in the season will help prevent overheating the soil during the summer. Wind protection will also help plants establish by preventing water loss from the plants and the soil. A hedge, snow fence, or row of tall garden plants on the windward side of the garden is useful. Shade from suspended snow fence or shade cloth (preferably white or aluminized) over the garden is also helpful. Adequate moisture in the soil applied by a drip irrigation system and mulch to conserve moisture are another factor that will help your garden next year. Excessive irrigation adds calcium and other mineral salts and can create problems. Heavy irrigation with good quality water to leach these minerals below the root zone may help, but requires adequate quantities of water. Drip irrigation helps avoid the problem in the first place by applying less water and mineral salts to the soil.

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!