Gardeners do everything they can to keep their plants happy and healthy, but sometimes, no matter what you do, certain plants just don’t go together. Plants that do not like each other may respond to different environmental needs, may compete directly with each other for major resources, or may attract insects that are severely damaging to each other.
Evaluating plant incompatibility can be a hypothesis and a test, as soil conditions also have an effect on which plants should not be placed together.
Incompatible Garden Plants
There are a few basic rules of thumb when it comes to plants to avoid near one another. First, check that your garden plants are all about the same size and have the same light requirements. Planting very tall plants like tomato next to bush beans, for example, is a very bad idea since the tomatoes will very likely shade out the beans.
If growing taller and shorter plants together, make sure the smaller plants are spread far enough and positioned so that the sun shines with them during the daytime. Many gardeners solve this problem by putting the shortest plants in their own row on the edge of the garden or planted as a border planting.
Plants that need a lot of water will cause those water haters nearby a great deal of discomfort; the same goes for fertilizer. It’s always a good idea to plant things with similar nutritional and water needs together, unless they’re fiercely competitive. Even then, you can often compensate by spacing them extra wide and providing enough fertilizer and water for both types of plants.
Last but not least are the plants that are allelopathic. Allelopathic plants have the capability to chemically impede the vital systems of competing plants. These plants are usually weeds, but many landscape and crop plants have been observed leaving behind allelopathic chemicals. Plant scientists are using these observations to develop better methods of weed control for farms and gardens alike.
What Plants Should Not Be Planted Together?
Several plants are claimed to have allelopathic behaviors, but many remain in the field of gardening and lack substantial scientific documentation. Research in this area is sparse, but the list of plants assumed to have allelopathic properties includes:
Black walnuts have long been known to interfere with garden plants like tomatoes, corn and eggplants.
When planting broccoli in your garden, make sure that you practice good crop rotation since broccoli can leave behind residue that other cruciferous crops can’t tolerate.
Some plants, like alfalfa seem to exhibit a remarkable type of allelopathy that interferes with the germination of their own seeds.
Garlic and onions are believed to interfere with the growth of beans and peas, but seem to be compatible with most other garden denizens.
Other commonly believed plant incompatibilities include the following plants to avoid near one another:
Mint and onions where asparagus is growing
Pole beans and mustard near beets
Anise and dill neighboring carrots
Cucumber, pumpkin, radish, sunflower, squash or tomatoes close to potato hills
Any member of the cabbage family near strawberries
Cabbage, cauliflower, corn, dill and potatoes near tomatoes