Zucchini squash can be used as a companion plant in several different combinations. The National Sustainable Agriculture Information Service describes companion planting as "the establishment of two or more plant species in close proximity so that some cultural benefit (pest control, higher yield, etc.) is derived. The concept embraces a number of strategies that increase the biodiversity of agroecosystems." Traditional farming wisdom says that zucchini squash should be planted with beans and corn. Corn offers a structure for beans to climb, beans replenish the soil with nutrients and zucchini squash leaves create shade mulch. Chemical secretions from zucchini squash may also be a factor in weed reduction. Other beneficial companion plants for zucchini are radish and marigolds.
Zucchini, Radish and Marigold Companion Planting
Choose a sunny garden location 3 feet square for each squash plant. Build a small mound of dirt for each. This creates a natural canopy effect for companion plants beneath the leaves.
Plant three squash seeds 1/2 to 1 inch deep at the top of the mound. Press the soil firmly, creating a small flat plateau. Squash thrive in full sun of 6 to 8 hours per day. When plants are 3 to 4 inches high and have two true leaves, thin to one strong plant.
Plant a circle row of alternating radish and marigold seeds around the base of the squash mound. Radish seeds such as the heirloom ‘French Breakfast’ are planted 1/2 inch deep. French marigolds reach a height of 12 to 18 inches. Plant the seeds 3 to 4 inches apart and thin as they become crowded.
Water thoroughly. Zucchini germinates in three to seven days, radish in three to eight and marigolds in three to 10 days.
Traditional "Three Sisters" Companion Planting Design
Shape a mound 2 feet tall and 2 feet across. Plant 5 to 6 corn seeds in a circle in the middle of the mound. Soak the seeds well and water each day until they sprout. Thin to three to five corn plants as they grow.
In two weeks, plant a circle of pole bean seeds around the corn when the corn is 5 to 6 inches high. Use 6 to 8 bean seeds, spacing them evenly and pressing 1 inch into the ground. Train the beans up the corn stalks as they grow and thin to two bean plants winding around each corn stalk.
One week later, plant six to eight zucchini squash seeds around the perimeter of the mound. Press 1 inch into the ground and water thoroughly until they sprout. The squash will vine alone the ground around the center mound of corn and beans.