Agronomy

Description

Classified as summer squash, zucchini fit in the cucurbit family, meaning that they’re related to crops such as watermelon, cantaloupe, cucumber and pumpkins. Zucchini squash are one of several summer squash types, and zucchini are also the most popular summer squash. Crookneck, straightneck and scallop squash are also summer squash types. The zucchini name originates from the Italian word zucchina, which means small pumpkin or squash.

Producers harvest summer squash like zucchini before the fruit matures. This makes summer squash different from winter squash, which aren’t harvested until they’ve fully matured and record longer shelf lives.

Site Selection

To grow zucchini, choose planting sites that drain well and have pH levels that range from 6.0 to 6.5. Planting sites should also have not recently grown other cucurbit crops, and those that have long-lasting herbicide residues or extensive nematode pressure also aren’t well-suited for zucchini production.

Zucchini are a potential high tunnel crop. Constructed from a steel or PVC frame and greenhouse-grade plastic, high tunnels may produce zucchini four weeks to six weeks earlier and six weeks later than observed when growing zucchini in a traditional field setting. Zucchini grow well when temperatures range from 75 degrees F to 85 degrees F. Nighttime temperatures shouldn’t drop to 50 degrees F or lower. If cold temperatures could damage plants, then low tunnels placed within the high tunnels can provide added insulation. High tunnel ventilation is important if temperatures warm too much. Because air in a high tunnel can be humid, the environment may promote disease development. Pollination may present a challenge in high tunnels raising summer squash. Producers may choose parthenocarpic varieties — those that don’t require fertilization to produce fruit — to address this issue.

Fertility

Fertility improvement needs will depend on soil test results. North Carolina Cooperative Extension recommends using 60 pounds to 80 pounds as a guide for nitrogen, phosphorus and potassium needs.

For optimal effectiveness, consider applying half of the prescribed nitrogen before planting. At that time, producers may also apply all phosphorus and potassium required. Producers may apply half of remaining nitrogen needed after zucchini plants reach an 8- to 10-inch height, and to support continued fruit production, they may apply the other half after they initially harvest zucchini from those plants. If they choose to not apply all potassium before planting, then producers could also divide potassium applications.

Variety Selection

Generally, summer squash varieties have a bush-like growing habit. Fruit color may differ by variety. Dark green, medium green, light green and yellow-orange colors are available. Depending on the variety, zucchini shape may vary from long, cylindrical fruit to round fruit. Disease resistance may also vary. Given that zucchini fruit attributes will depend on the variety, producers should choose characteristics and varieties that meet an end market’s standards.

Recommended Zucchini Varieties

Planting

Zucchini plants may get their start as seeds or transplants. Alabama Cooperative Extension describes that producers may experience the best results if they directly seed summer squash. Varieties can cross pollinate with other summer squash and related plants such as acorn squash and jack-o’-lantern pumpkins, so producers shouldn’t use any crossed seed for planting. If producers choose to plant summer squash transplants, then be mindful that transplants can be sensitive to shock. This is especially a problem when they stay in greenhouses too long.

Producers should postpone planting summer squash until soil temperatures reach levels that would support seed germination. Planting also should only occur after frost no longer presents a challenge. University of Missouri Extension recommends planting zucchini from May 1 to May 30 in southern Missouri, May 10 to May 30 in central Missouri and May 15 to May 30 in northern Missouri.

If the planting site has raised beds and black plastic mulch, then the soil may warm more quickly. When using plastic mulch, the soil may also experience diminished compaction and crusting, fruit may have minimized ground rot, fertilizer may leach less, crops may have a reduced drowning risk, moisture may evaporate less, and weeds may be managed. Producers may also accelerate the zucchini production season’s start by using row covers, reorganizing the row orientation or planting transplants.

By staggering planting every 10 days to 14 days, producers can position their operations to produce zucchini throughout the growing season. The last planting may occur 60 days before the frost date; however, late-planted zucchini may be more susceptible to disease and insect pressure.

Cultural Management

Zucchini are monoecious plants, meaning that a single zucchini plant produces both male and female flowers. Because wind won’t adequately carry pollen from male to female flowers, pollinators are necessary. By positioning a commercial beehive near the zucchini production area, producers can support pollination. Wild honeybees have had diminishing populations, and this had created a need for using commercial beehives. Use one hive per acre. If summer squash have neighboring plants that bloom at a similar time, then those competing blooms may draw bees from summer squash blossoms, which supply relatively little nectar and pollen for pollinators.

If zucchini plants haven’t been properly pollinated, then young fruit may change to a yellow color, develop a shriveled appearance and drop to the ground, or the fruit can develop into off-shapes with no market opportunities. Avoid irrigating zucchini fields and applying pesticides when bees are active.

Water Management

To maintain production levels, zucchini plants weekly need an estimated 1 inch of water. If the planting area has sandy soils, then more water may be needed. Summer squash that lack adequate moisture during fruit sizing may yield squash with pointed and off-shaped characteristics.

Weed Control

Weed competition can limit zucchini yields. To minimize weed problems, choose a planting area free from continued perennial weed pressure. Weed species such as pigweed, lambsquarter, cocklebur and ragweed may present a challenge for zucchini production. If zucchini plants grow quickly enough, then they can canopy and minimize weed pressure.

By preparing the planting site and irrigating it before planting, weed seeds may germinate, and producers may then use mechanical operations to eradicate those weeds. As another option to manage weed populations, producers may consider herbicide applications. However, squash plants may not always respond well to herbicide exposure. Additionally, cultivation operations should avoid disturbing shallow, sensitive zucchini roots.

Insects and Diseases

Zucchini may experience aphid, cucumber beetle, pickleworm, squash bug and squash vine borer outbreaks. To control such insects, producers may apply pesticides. Rotating crops is another alternative.

Diseases such as powdery mildew, downy mildew and those transmitted by viruses may afflict zucchini crops. Other possible zucchini diseases include angular leaf spot, phytophthora blight and mosaic viruses. By adopting an appropriate crop rotation, producers may control disease issues. Rotations with pasture grasses and small grains may be especially effective. To manage viral disease risk, producers may plant zucchini early. Doing that may enable the crop to establish itself before it experiences pressure from insects that carry viruses. Other disease prevention strategies include choosing resistant varieties, applying fungicides and sanitizing production processes.

Blossom end rot, which manifests itself as watery, black lesions, may also present a problem in zucchini production. The condition, which is frequently associated with tomatoes, stems from a calcium deficiency.

Harvest and Storage

As mentioned earlier, producers harvest summer squash before the fruit has matured. After flowering, zucchini mature quickly. Because of their fast development, zucchini may need to be harvested either every day or every other day. Zucchini will be ready for harvest when they measure a 1.5- to 2.5-inch diameter and an 8-inch length. The fruit should still have a glossy appearance, and seeds shouldn’t have grown too large or hardened. When harvesting zucchini, leave a 1- to 1.5-inch stem. As a zucchini plant matures, it produces fruit with lower quality. To optimize crop quality, harvest fruit for just two weeks to three weeks per planting.

Producers should take caution when harvesting zucchini. The fruit can easily bruise or scratch. Experts recommend cutting zucchini stems. If producers wear cotton gloves during harvest, then they may protect the fruit from scratches and punctures. To clean zucchini fruit, use a clean, dry cloth, which can remove dirt and dust.

After harvest, summer squash like zucchini have a short shelf life. As such, they require quick marketing and generally aren’t stored. If they are stored, then zucchini quality may degrade quickly. Producers who must store zucchini should create an environment with temperatures that range from 41 degrees F to 50 degrees F and 95 percent relative humidity levels. When storage temperatures are too cool, zucchini can develop chilling injury, which is characterized by surface pitting, discoloration, browning and quality degradation. After being stored for more than two weeks, shriveling, yellowing and decay become concerns.

Sources

Blue Book Services. 2015. Zucchini Know Your Commodity References. Blue Book Services. Carol Stream, IL 60188-3520.

Boyhan, George E., Darbie M. Granberry and W. Terry Kelley. 2014. Commercial Squash Production. University of Georgia Extension. Athens, GA 30602.

Drost, Dan. 2011. High Tunnel Summer Squash Production. Utah State University. Logan, UT 84322.

Kaiser, Cheryl, Matt Ernst and Shawn Wright. 2014. Summer Squash. University of Kentucky. Lexington, KY 40506.

Kemble, J.M., E.J. Sikora, M.G. Patterson, G.W. Zehnder and E. Bauske. 2005. Guide to Commercial Summer Squash Production. Alabama Cooperative Extension System. Auburn University, AL 36849.

Molinar, Richard, Jose Aguiar, Mark Gaskell and Keith Mayberry. 2012. Summer Squash Production in California. University of California. Davis, CA 95616-8699.

Schultheis, Jonathan. 2005. Summer Squash Production. North Carolina State University and North Carolina A&T State University Cooperative Extension. Raleigh, NC 27695.

Suslow, Trevor V. and Marita Cantwell. 2013. Squash (soft rind): Recommendations for Maintaining Postharvest Quality. University of California. Davis, CA 95616-8699.

Trinklein, David H. 2015. Vegetable Planting Calendar. University of Missouri Extension. Columbia, MO 65201.

University of Illinois Extension. 2015. Summer Squash. University of Illinois Extension. Urbana, IL 61801.