JoAnne Skelly: Fascinating interactions among plants

As I wrote last week, there are biological, chemical, and physical advantages and disadvantages to growing certain plants together.

I had excellent tomato and lemon cucumber yields last year. Many factors may have contributed to that success: optimal temperatures, good soil, sufficient amount and timing of water, and abundant pollination.

Did interplanting them with dill, a supposed “companion plant” for each, help? Since dill flowers attract pollinators, perhaps it increased successful pollination. Although self-pollinating, with both male and female parts within one flower, visiting bees and such possibly shook the pollen around, getting it to the female parts.

Cucumbers do need pollinators to move the pollen from the male flowers to the separate female flowers. Perhaps the dill flowers brought pollinators in, and then they discovered the cucumber flowers. I can’t prove the dill helped, but I will plant it again.

Many other flowers and herbs also attract pollinators to the benefit of crop yielding plants. Often soils are high in salts, sometimes dangerously so for certain plants.

Halophytes are plants that grow in high sodium soils. They pull salts out of the soil to the benefit of less salt-tolerant species. Halophytes include a variety of grasses, shrubs, and trees. While they are not actually “companions,” salt reduction in a soil may allow other plants to grow in formerly poor soils.

Some deep-rooted plants such as watermelon or asparagus can pull nutrients and water from deeper in the soil making these available to other plants. Plants with taproots such as carrots or radishes can break up soil compaction.

Allelopathy describes the chemical interactions of plants for benefit or detriment. Allelopathic plants often produce and release toxic compounds into the soil or air, which can inhibit other plants. Broccoli beds shouldn’t later be planted with other cruciferous vegetables such as cabbage, Brussel sprouts, etc.

Sunflowers and goldenrod can have negative allelopathic effects. Very few plants can grow under black walnut trees. This negative chemical influence can be put to good use when it works to suppress weeds.

Rye, fescue, and wheat are good cover crops to reduce weeds. Their residue, when retained as mulch, is also an effective weed barrier. I mentioned mycorrhizae last week, fungi with a beneficial relationship with the roots of many plants.

Although fungi aren’t plants, they play an important role in plant nutrition by attaching to plant roots and increasing their nutrient absorption surface area. They often also provide some protection against soil-borne diseases.

Eighty percent of plants have these symbiotic relationships with mycorrhizae. Perhaps “companion plants” share the same mycorrhizae. My fascination with the plant world continues.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.