Tips from the Potting Bench

Companion planting is a method of planting that increases biological diversity and takes advantage of beneficial plant interactions. Some plants just do better when planted with certain other plants, they grow better or may taste better or are protected from damaging pests. It is a method of planting that has stood the test of time and science, it’s fun and looks good too.

In the middle of the last century Dr. Ehrenfried Pfeiffer developed a test to measure which plants would interact well with each other. He called the test sensitive crystallization and it works like this: plant juices are mixed with a salt based reagent like sodium sulfate or copper chloride, the solution is put in a controlled chamber where it is allowed to slowly dry out. What is left when all the water evaporates is a crystallized geometric pattern. The pattern is interpreted to establish if the plants are likely to interact well with each other. The more pleasing the pattern the better the pants are for each other. A complete list of plants that work well with each other is available on line by goggling ‘companion plants’.

There are a number of ways to create beneficial plant associations, the following are a few you may want to try. Trap cropping is when a neighboring crop is used to attract pests and distract them form the main crop. An example of this is using collards to attract the diamond back moth away from cabbage. Some crops fix nitrogen from the air to use for themselves, plants growing nearby also get the benefit of this added nitrogen. This is the reason I planted my cucumbers into the row where the peas were. Legumes, beans and peas can take nitrogen out of the air and transform it into something they can take up through their roots. Another good example of this is planting beans with corn. Corn is a notorious nitrogen hog, planting beans alongside the corn can decrease the amount of fertilizer the corn needs. This is called symbiotic nitrogen fixation.

Biochemical pest suppression is based on the fact that some plants exude chemicals from their roots, leaves, stems or flowers that actually repel pests. An example of this is using African marigolds to repel nematodes. Another really great example is using a cover crop of rye; once it is mowed down it releases chemicals that prevent weed seeds from germinating but doesn’t hurt veggie transplants. Another easy method you can employ is based on physical spatial interactions or using a tall crop to protect a shorter crop. Sunflowers planted with lettuce for example. This method also works by confusion. The canopy of the taller plants confuses the pest, keeping them out of the lower growing plant. An example would be corn growing with squash or pumpkins. The corn canopy confuses the squash vine borer and the prickly squash plants may deter rascally raccoons from stealing the corn. Taller crops can also be used as a wind break.

The last method I want to talk about is one of my favorites, creating beneficial habitats. That is creating places in your garden to attract the good bugs to come and live. You will need to provide food, shelter and water for these good guys to hang out in. Food is provided by growing certain plants that will provide nectar and pollen for when they aren’t eating the unwanted bugs. Water can be from overhead watering or a decorative bird bath. Shelter is easy because you are mulching your garden beds to help conserve water and adding organic matter, so the mulch will also act as shelter for the beneficial bugs. The best part is that you need to plant lots and lots of flowers; the trick is to plant so that there is always something in bloom for the beneficials to eat. The best flowers are those that are open faced, so the beneficial bugs can easily get to the nectar, like tansy, yarrow, fennel, marigold, cosmos, sunflowers, mints, lavenders, zinnia, asters and the list goes on. By creating a corner in your garden that is just a little bit wild and full of color you can be sure that lots of the bugs you want will be around helping to create some balance with the unwanted bugs.

There are a number of places on line that list specific plant combinations as well as places that will tell you exactly which plants attract which bugs. Check them out and give it a try. It’s easier and more earth friendly than spraying and it sure looks a whole lot nicer too.

Try mastergardeners.org for a good list of plants and who they attract.