CORVALLIS, Ore. – An ancient practice of growing two or more vegetables in the same place at the same time, called interplanting, is becoming common again.
The extra planning required can be worth it for the additional growing space it provides, said Pat Patterson, Master Gardener volunteer with the Oregon State University Extension Service in Lane County.
"Interplanting also helps keep insect and disease problems under control," she said. "Pests are fairly crop-specific and prefer vegetables of one type or family. Mixing plant families breaks up expanses of crops and confines early pest damage to a small area."
This practical growing method can foster symbiotic relationships as well. American Indians from the Iroquois tribe planted corn, beans and squash in one mound as "three sisters" who needed each other to grow. Beans fix nitrogen, which corn needs in large amounts. Corn reciprocates by lending its stalks for climbing beans. The broad leaves of squash shade out weeds and retain moisture in the soil.
Patterson recommends the following factors as you plan to interplant:
Time to maturity:
Slow-maturing (such as carrots) and quick-maturing plants (such as radishes), can be planted at the same time. Harvest the radishes before they begin to crowd the carrots.
Above-ground growth pattern:
Planting small plants close to larger plants, for example, leaf lettuce and radishes at the base of pole beans or broccoli, is an example of combining growth patterns.
Root growth pattern:
Combine plants with complementary root-growth patterns so that roots won't compete with each other. Shallow rooting plants include broccoli, corn, lettuce, potatoes, cabbage and spinach. Medium rooting are snap beans, carrots, cucumber, summer squash, turnips and peas. Deep rooting include asparagus, parsnips, winter squash, pumpkin and tomatoes.
Possible negative effects on other plants:
Don't plant sunflowers and Jerusalem artichokes, which can suppress growth of nearby plants, close to other crops.
Plant shade-tolerant species such as lettuce, spinach and celery in the shadow of taller crops.
Season of growth:
Interplant cool-weather and warm-weather plants. By the time warm-weather crops grow to full size, the cool weather crops will have finished producing.
Interplant heavy feeders such as cabbage family crops with less demanding plants such as carrots, garlic and parsnips.
Group plants with similar water requirements together to avoid over-watering some or to supply enough for others.