April 4, 2015

1 - Crop rotation in the home garden is a good idea to prevent disease problems and to better utilize soil nutrients.

Yard and Garden April 4, 2015


Last year I grew tomatoes for the first time on this property. I want to grow them again this year, but I was told that I should not grow them in the same space. Is this true? Why? I really do not have another location available this year.

- KDAZ radio call-in


Crop rotation, moving plants to different locations in the garden is a good idea. The reason for not growing the same plant, tomato or other crop, in the same location year after year is to reduce the accumulation of disease organisms in the soil at that site and to allow better nutrient utilization.

If the same crop or related crops that are subject to the same diseases are grown year after year in the same location, the disease organisms may build up to levels that cause crop failure. Changing to crops that do not harbor the same disease organisms helps reduce this problem. Addition of well-made compost also helps reduce the incidence of disease accumulation in the soil. Tomatoes, potatoes, chiles, egg plants, and some other plants in the Solanaceae plant family should not follow each other in a garden. Beans (Fabaceae family), corn (Poaceae family), squash (Cucurbitaceae family), and certain other plants are better choices for following tomatoes. The tomatoes should be rotated to different areas and not returned to any previous location for about 4 years if possible.

There are disease organisms that can infect several of the plants listed as good for following tomatoes in the garden. Properly made compost added to the garden soil will help reduce the chances of these organisms accumulating by putting beneficial organisms in the soil to compete with the disease organism for niches in the soil environment. If diseases do develop over time, it may be possible to reduce the problem by solarizing the soil. Solarization is the solar heating of the soil to a pasteurization temperature (160 degrees) by covering the moistened soil with clear plastic. The edges of the plastic should be sealed to the ground by covering with soil, rocks, or boards. Sunlight passing through the plastic warms the soil. The plastic with a layer of condensed moisture on its underside hold the heat in by the greenhouse effect. In the New Mexico environment, the temperature of the soil will rise fairly rapidly, especially in the summer. A soil thermometer, or longer stemmed compost thermometer, can be used to determine the depth to which pasteurization temperatures penetrate the soil. Sticky tape can be used to seal the hole after checking the soil.

Having said all that, since you have only grown tomatoes in that location once before, if it is not possible to move them to another location this year the chances of a disease developing are not great. You should plan for crop rotation in the future.

Another reason for rotating crops is that by changing crops to those that use different proportions of nutrients from the soil, you can help maintain soil fertility and allow recovery from the depletion of nutrients by each crop. Addition of compost also helps with this. Soil testing periodically to determine the nutrient status of the soil and to identify nutrients that should be applied as supplements to the soil is also a good idea. Applying fertilizers to replace nutrients without knowledge of the nutrient status of the soil may not result in good crop production. Your local NMSU County Extension Service office can help you find a soil testing laboratory and help you understand the test results that you receive from the laboratory.

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!