1 - Roses do not poison their soil, but there are several reasons roses do not do well where other roses have died.
Q. Help! We have a very nice micro-climate for roses along our driveway but do lose a plant every now and then, largely through neglect. We have had no luck with planting other roses in the place where a rose has died. A friend says that roses "poison" the soil they grow in so that other roses will not thrive in the same locations. Obviously there is a solution to this problem. What do you advise? My husband has tried removing the old soil and replacing it with potting soil, but that doesn't work very well.
A. There are several possible meanings to your friend's suggestion that the rose plant has "poisoned" the soil. Some plants do create allelopathic chemicals that inhibit the growth of other plants, but not themselves and their own kind. These chemicals are to inhibit the growth of other species that would compete with the plant producing the chemicals. Salt cedar and walnut trees are examples of plants using "chemical warfare" to inhibit competition. However, some other plants are not affected by these allelopathic chemicals. I have not seen reports of garden roses producing such chemicals, so that is probably not the cause of your problems. It is possible that plant pathogens (fungi or bacteria) can buildup in the soil around the roots of infected plants. These may indeed affect the growth of new plants of the same type (roses in your case) that are planted in that soil. This is the reason gardeners are advised to rotate their crops in their vegetable gardens. This usually relates to annual crops, but can affect perennial plants as well. If there may be a disease involved, your local NMSU Cooperative Extension Service office can send samples of the plant (roots or other tissues) to the NMSU Plant Disease Diagnostic Laboratory in Las Cruces. Contact your local Extension Office to determine what samples they need. Since you mentioned neglect as a possible cause of plant death, disease may, or may not, be involved. Another possibility is nutrient depletion by the plant, or accumulation of excess nutrient salts from over fertilization. A soil test can help determine if there are salts, excess or deficient nutrients, or other soil factors causing your problems. Once again, your local NMSU Cooperative Extension Service office can help you. They can advise you as to the proper method for collecting the soil sample. They can direct you to an appropriate soil testing laboratory, and they can help you interpret the soil test results that you receive. They can also give you NMSU Extension publications on this and other topics. Before spending money and energy replacing soil or trying other things, it is important to diagnose the exact problem. The NMSU Cooperative Extension Service is there to help you do this. To find your local NMSU Cooperative Extension Service office you can go to http://aces.nmsu.edu/county/. You can find many of the publications I mentioned in this and other articles at http://aces.nmsu.edu/pubs/howto/howto.html.
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: email@example.com, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!