1 - There are numerous things that can stunt garden plants.

Yard and Garden - May 28, 2011

Q.

For the past 4-5 years my vegetables, tomatoes, sweet peppers yellow hot peppers, etc. have refused to grow even an inch. In August they are the same size as the day I bought them at the nursery. Yard flowers also refuse to grow in the garden or in soil taken from the garden. I always wait until ground temperature is 55 degrees 6 to 8 inches below surface.

I have had the soil tested by NMSU, they say soil is good, I add commercial cow manure from Home Depot, Lowe's etc every fall and several weeks before planting. The only other additive I use is Miracle Grow which I dip the roots in when planting and mist the leaves once a week. Never have used pesticides, weed or grass killers anywhere.

At a total loss except for something I have been doing for several years. Each fall the neighbors give me the leaves from their Mulberry trees which I till into the garden and water frequently to help decay.

Could Mulberry leaves cause stunting? I know Walnut and Pecan, pines etc. leave are not good for gardens.

- Larry C.

A.

This is a challenging question. You have considered most of the factors that could cause the problem and done as I would have recommended. However, there are a few things I want to consider. You said that NMSU Soil and Water Testing Laboratory said the soil was good. In the test results were the dissolved solids (salts) high? Addition of manure over time can raise the level of salts in the soil. These salts can inhibit root growth. You can talk to your local NMSU County Extension office about your soil test results and the salts in the soil if you are unsure if the salts are high enough to cause a problem. The fact that you have added manure in the spring (I assume after the soil test), may have increased the salts. However, with adequate irrigation, the salt level should have decreased through the summer and the plants should have exhibited growth.

A second consideration is viral diseases of these plants. Tomatoes and chiles are subject to infection and stunting caused by curly top virus and tomato spotted wilt virus. Once again, your local NMSU County Extension office can help you by sending samples of stunted plants to the NMSU Plant Disease Diagnostic Laboratory. Many people have reported problems with these viruses for the last several years.

Since you mentioned your neighbor's mulberry trees, another consideration is root competition for water and nutrients caused by the mulberry trees. Their roots can extend at least 4 times the height of the tree and can cause problems within that range. Do you find numerous small (water and nutrient absorbing) roots of trees in the garden when you are digging or planting? This could contribute.

Finally, to address the question of the mulberry leaves and their allelopathic properties. Research at some universities has shown some inhibition of seed germination (lettuce and radish) caused by water extracts from fresh, dried, and ground white mulberry leaves. Other research has shown that in older plants (transplants) some grasses are inhibited and some stimulated. I found no references to inhibition of tomato or chile seedlings. Since you are composting the leaves (working them into the soil), it is likely that the decomposition process has reduced or eliminated any chemicals that would inhibit the growth of your transplants. However, the possibility of allelopathic inhibition cannot be ruled out completely. This is true especially if large quantities are rototilled into a small garden annually. The chemical may be accumulating over time. The fact that other plants did poorly in that soil as well(you did not name the flower species that would not grow there), suggests that this may be a factor.

Finally, how long have you been at that site? If a previous owner used certain herbicides with long persistence in the soil, then the herbicides (that you did not apply) may be a factor.

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.

Links:

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