Companion Planting

Companion planting is the practice of arranging plants next to one another for beneficial effects. It can look kind of wild.

Chard, Carrot and  Lettuce nestled
under Pole Bean vines. 

A well known example of companion planting is "three sisters", corn, beans and squash. Others include tomato with basil, and blueberry with rhubarb and raspberries. It also seems that many things which go well together in a meal or snack also grow well together. But not always- I love an apple pie with walnuts and raisins baked in. While grape and apple get along fairly well, the grape will overwhelm the apple without lots of care, and if you put either too close to a black walnut you might as well have soak them with kerosene.

One can find numerous examples of companion planting with a quick google search, and if all a person is interested in is are few hints on what combinations work, that will do just fine. How a specific group of companion plants work together is a completely different set of inquiries. Chemical, structural, and spatial relationships, or 'niches', drive the compatibility- and adversity- of plants. In any given planting these three qualities interface in dynamic relationships that change over both the course of the season and the life of the plant.

Peas are leguminous, and, working with soil bacteria, make nitrogen in the soil available to other plants. Peas benefit most things that they can be grown next to by increasing the soil fertility. Beets, celery and potatoes can all benefit from this. Take it up a notch by planting them next to perennials such as small fruit trees, open structure shrubs, and deciduous bushes where they can climb and vine.

Plant 'niches' are a plant's structural habit and soil/light/heat preferences. The habit of tomatoes is lightly vining and sprawling. They don't need deep soil, but do prefer well drained, warm spots with lots of water. In the tropics I have seen cherry tomatoes growing in massive tangled mats at the high mark of water scour on swift moving streams. They like an acidic soil rich in minerals but have a high tolerance for low organic content. For instance, the San Marzano, a cultivar developed nearly 300 years ago following a gift of Seed from the Viceroy Of Peru to the Kingdom of Naples. Treasured for its rich paste and hearty soup flavors, it grows prolifically and has naturalized in the ground up basaltic soils inundated with springs and seeps at the base of Mt. Vesuvius.

When we know a plants soil needs and growth habit, we can begin to consider who it might thrive with. For instance, blueberries do well in well drained, acidic soils and find vigor in high mineral soils. They also can provide some woody structure for a weak vine to hang from and climb in. However, tomatoes, and the San Marzano in particular need  heat to get ripe- enough to  burn a blueberry. Peas are a better choice, ripening early enough to be harvested and removed from the blueberry before it produces fruit. Still, peas may struggle with the soil acidity and water tolerance blueberries are known for. Companion planting asks us to consider plants niches and how they will interface with neighboring plants.

Early I mentioned one might as well go about watering apples with kerosene as planting them next to a black walnut. Walnuts are part of a genus called Juglans, and are known for producing juglones, powerful chemical hormones which prevent many other plants near them from growing- this is why the ground under large old walnuts is often bare or sparsely vegetated. Apples don't do well when exposed to juglones. However, a solid handful of plants are not only able to survive and thrive in this environment, some actually create buffers so that the tendency of juglones to saturate the soil is mitigated. Examples of these plants include Serviceberry, Persimmon, Mayhaw, Pawpaw, Elderberry, Goji Berry, Redbud, Mints, and Daylillies. However, the Walnut will outlive many of these, and in time a young walnut will grow over and heavily shade these companions. So we must think about the assembly over time, rotating in new companions every few years to decade as the tree grows, using plants that can tolerate the high juglone and heavily shaded conditions under the canopy.

This year in the Learning Garden we put in several known companions: Kale, peas, and turnips; rosemary, chives, and strawberries, carrots, peas, and lettuce. Kale, peas, and turnips work largely because they fill different structural places in the garden. They don't get in each others way. Rosemary, fava, chives, and strawberries  are similar. While rosemary's strong volatiles drive away aphids and leaf miners, fava's nitrogen fixing effect provide chemical benefits to the soil.

Comfrey used as a 'chop and drop' mulch around a small tree.

Let us not forget the weeds. Many 'weeds' are powerful allies in the garden assembly. Dandelions, comfrey, and dock, pull nutrients up from deep soil. when the leaves decay those nutrients can be reached by shallower rooted plants like lettuce and peas. By letting these garden allies grow just to the point of flowering, and then leaving the root but pulling the flower or unripe seed pods and leafy greens, we can excellent minerals and nutrients to the soil. Nitrogen, phosphorus, and potassium, as well as magnesium, selenium, boron, iodine and other trace nutrients plants (and our bodies) need become available to plants this way. They also provide ground cover, providing moisture retaining shade at the ground level as a living mulch.  Dandelion, comfrey, and dock, will re-sprout if you leave the root in the soil and remove just 3/4 to 7/8 of the greens. The leaves, etc., can be used in compost or just as 'chop and drop' mulch.

Companion planting is kind of wild. But then so is a forest. And just like a forest, the plants in our garden aren't here just for us, they also are bound to one another. By recognizing the  natural relationships plant communities use to create prosperity and resilience, we can learn something of how to best meet our needs while remaining in harmony with nature.