Trellises can save time and trouble when you're raising vine vegetables such as zucchini (Cucurbita pepo). Trellises economize your garden space, let you work on your plants while seated or standing, and dramatically reduce problems caused by pests and diseases that affect the bases of plants. Beyond training your vines to growing vertically in their early stages of development, the cultural practices you use to grow zucchini on a trellis aren't different from what you do to grow them on the ground.
Select area where the zucchini can get full sunlight, and cultivate the soil 8 to 12 inches deep as soon as the ground warms up enough in the spring to be worked with a spade fork. You need an area at least 8 feet wide and 6 feet long to plant one row of zucchini on each side of the trellis.
Sprinkle 4 cups of water-soluble, granular, 10-10-10 NPK fertilizer over every 50 square feet of planting area, and spread 3 to 4 inches of compost over it. Work the fertilizer and compost in 8 to 12 inches deep, using a spade fork for the task. Water the fertilizer and compost in with 1 to 2 inches of water.
Install a 5- to 6-foot tall, 5-foot wide, A-frame trellis with four crossbeams lengthwise in the center of the planting area. Plant zucchini seeds 1 inch deep in two rows, one on each side of the trellis. The soil should reach 60 degrees Fahrenheit at a depth of 4 inches before you plant. Space the rows about 6 inches from the trellis; space the seeds 3 to 4 inches apart in each row.
Water the soil with 1 to 2 inches of water after planting. Water the soil to a depth of 6 inches once a week on the same day thereafter.
Cover the rows with polypropylene row covers until they reach about 4 inches tall and develop their first sets of true leaves -- about 1 month after planting. Drape the row covers over 12-inch-high U-shaped wire hoops inserted in the ground at the ends of each row to keep the row covers off the soil.
Remove the row covers when the zucchini plants reach about 4 inches tall. Pull up the weakest plants, leaving the healthiest zucchini plants spaced 12 inches apart along the rows.
Mulch the zucchini plants with 2 inches of bark chips, pine needles, shredded leaves or other organic mulch. Keep the mulch 1 to 2 inches from the stems.
Tie each zucchini vine loosely to the bottom crossbar on the trellis as soon as it grows tall enough -- 6 to 8 inches tall. Space the vines 12 inches apart on the crossbar. As the vines grow, tie them to the next highest cross bar, and remove the twine from the cross bar below it. You can stop tying the zucchini to the trellis when the vines begin growing on it by themselves, usually after two months.
Sprinkle 1 tablespoon of water-soluble, granular, 21-0-0 NPK or 33-0-0 NPK fertilizer around each zucchini plant when the vines start to develop offshoots or runners. Keep the fertilizer 6 inches from the plants when sprinkling it on the soil. Water the fertilizer in with 1 to 2 inches of water.
Pull any weeds the mulch doesn’t suppress as you see them. Zucchini doesn’t like competition.
Scan the plants routinely for squash bugs, cucumber beetles and aphids. Aphids that attack zucchini measure about 1/16 to 1/8 inch long, have green or black bodies and congregate on the leaf bottoms. Cucumber beetles measure 1/4 to 1/2 inch long, have green bodies with black stripes or spots, and eat leaves and bore into roots. Squash bugs suck the sap from leaves, have grey bodies that measure about 5/8 inch long, and leave behind excrement, which looks like small dark spots.
Pick squash bugs and their larvae from the leaves by hand and step on them. Spray aphids from the plants with a strong spray of water from the hose. If you have a serious aphid problem, mix together 2 1/2 tablespoons of insecticidal soap containing 49.52 percent potassium salts of fatty acids with 1/2 gallon of water in a spray bottle, and spray the pests until saturated. Repeat every week as needed.
Mix together 1 tablespoon of a pesticide containing 1 percent pyrethrins and 10 percent piperonyl butoxide with 1 quart of water in a spray bottle at the first sign of cucumber beetles. Spray the tops and bottoms of the leaves until covered.
Cut the zucchini from the vines about 55 days after planting, or when they grow to 7 or 8 inches long, using pruning shears or a serrated knife for the task. Leave about 1/2 inch of stem on each zucchini.