I am often asked what chemicals I use to keep down such pests in my garden such as aphids and slugs. I say, “I don’t.” Instead I do what is commonly known as “companion planting.” Simply put, companion planting is placing a plant that tends to repel certain bad insects with a plant that tends to be plagued by those same insects. Companion planting is also used to promote the growth and overall health of plants. I have practiced companion planting for a few years with a great deal of success. In fact, I no longer use pesticides of any kind. I would like to share with the reader some of the companion planting that I have personally found to be quite effective.
Probably one of the things that I am asked about in my Zone 6 area is: “Why aren’t aphids eating all of your plants?” What I have found to be the most effective deterrent to aphids is nasturtiums. Nasturtiums are generally considered to be an herb. They are even edible, having a spicy, peppery flavor. (You can use them in salads and use the seeds and buds instead of capers.) They were one of Thomas Jefferson’s favorite flowers. Nasturtiums are a favorite food of aphids. So why plant them? The aphids will flock to the nasturtiums and leave your broccoli and cabbage alone. This past spring in my home state of Tennessee, we had a nasty (and early) infestation of aphids in my area. I could not get the nasturtiums in the ground fast enough! It did not take very long for the aphids to leave my roses and my brassicas alone. If you are bothered by aphids on your nasturtiums, you can just give them a good spray with the hose. I did not, however, notice many on mine. Nasturtiums should be planted in the spring, around May. You can also start the seeds inside and then transplant. They will also bloom through the summer and well into the fall.
Another problem that is easily solved by companion planting is slugs. Slugs just love dahlias. This is why I plant my dahlias near my artemisias, since artemisias repel slugs. I have not had a single problem with slugs munching on my dahlias. You can plant your parsley near artemisias, as well, which is another favorite of slugs. (Another interesting thing about artemesias: cats do not seem to like them.)
Yarrow, which comes in numerous varieties and colors, is sometimes called the “plant doctor.” It tends to make plants around it heartier and more disease-resistant. It is good for your compost, too, because it promotes faster decomposition. (Comfrey does the same, so you might want to plant it near your compost pile.)
Some plants can even repel critters — those squirrels and chipmunks that just love to steal bulbs out of your garden. I had one little chipmunk last year trying to run off with a lily bulb (and stem) that was five times his size. I immediately grabbed a garlic bulb out of my kitchen and proceeded to plant garlic gloves around my various bulbs. (You do not have to do this with daffodils, since these bulbs are poisonous to the critters so they leave them alone.) Of course, you will have garlic popping up all over in your garden in the spring, but you can just cook with it. (I use the tops just like chives, which critters are not fond of either.) By the way, the little chipmunk stayed away. They do not like the smell of garlic.
Herbs are your best choice when it comes to any type of companion planting. They tend to be aromatic, which confuses the bad bugs; therefore, they just stay away. At the same time, the scent and flowers of the herbs attract the good bugs to your yard, many of which will munch on the bad bugs for you. Bee balm and lemon balm are great choices. The various mints available are also perfect for attracting good bugs. You can grow your mint in containers if you do not want to have it take over your yard, and it will even come back the next year. In addition, herbs can actually help the growth of other plants. Feverfew and dandelions (yes, the dandelion is an herb) are great for planting around apple trees. They help the fruit to mature faster by attracting more bees for earlier pollination. Catmint is often used as a border for rose gardens. Not only does it hide the base of a rose, which tends to be a bit unsightly at times, it also puts nutrients back into the soil that roses like. Sage will encourage the growth of your strawberries and give you a sweeter berry. Tansy is good around blackberry bushes. (However, tansy is very invasive, so you might want to place it in containers.) The blackberry bush I had planted next to tansy grew faster and larger than the one I did not have any tansy near.
There are some plants that should not be planted together. For example, onions and tomatoes do not play well together; however, with just a little research, you can improve the health of your garden and eliminate (or, at least, curtail) the use of chemical insecticides. Finally, your garden will be even more pleasing to the eye, since most of the plants that work well for companion planting tend to be quite lovely in their own right. And you have also helped the earth.