Growing a Bountiful Zucchini Crop

Finally the time has come to plant warm season crops. Zucchini is a popular summer squash grown throughout Indiana and the United States. It always delivers a bounty of fruit. Yes, technically zucchini is a fruit (botanically classified as a modified berry) but as per the USDA it is listed under the ‘Vegetables and Vegetable Products” food group. Zucchini have a multitude of fruit colors and flavors. Therefore, this makes a great vegetable to present to consumers.

Characteristics of zucchini – Typically, zucchini is non-vining and bushy but some varieties could have a creeping habit. Some varieties have prickly trichomes on both the stems and leaves. Male and female reproductive structures are produced on the same plant but in different flowers. The large yellow-orange unisexual flowers (a flower that possesses either stamens or carpels but not both) attracts bees, beetles and other insects to pollinate the flowers. The pollen is heavy and sticky and does not transfer without the intervention of insects or people. Some varieties might be parthenocarpic. Meaning these varieties have the ability to set fruit without fertilization of the ovule. Producing parthenocarpic fruit have some advantages. The fruit is seedless, have a longer shelf life, and it requires less labor to process. In addition, parthenocarpic varieties are not affected by varying climatic conditions and therefore will produce yields that are more reliable. However, there are few parthenocarpic varieties available. The fruit can be dark or light green, or have a deep yellow or orange color.

What to look for when choosing a zucchini variety? – Zucchini is a fast-growing plant and can reach maturity within 40 and 55 days after seeding, dependent on the variety grown. The rule is, get the crop in and out fast. You might consider planting successive plantings throughout the season and not plant a vast area all at once. The plant is most productive for a two to three-week period and should be subsequently terminated after four weeks. For continuous supply, another planting should be harvested from week three. The structure of the plant is important, especially if you are in an area that is prone to strong wind gusts. Wind can twist and snap the plants off. During our 2018 variety evaluation one variety stood out above the rest. The variety ‘Green Machine’ did not twist under strong wind conditions. Choosing a compact or strong semi-open variety might be the right option for windy areas. Plants that have a strong upright structure will make it easier to reach in during fruit harvesting. Pay attention to comments about spines (trichomes). Some varieties have spineless petioles. Growing spineless varieties will allow you to harvest the fruit faster and have fruit that looks more appealing and have a longer shelf life. Be careful when using varieties with spines. Fruit could be punctured and scratched during harvest. Labor harvesting fruit need to wear long sleeve shirts and gloves to prevent their arms and hands from being scratched and becoming irritated. Choose from a variety of fruit colors. There are several shades of green and yellow and some varieties produce glossier fruit. The thickness of fruit can also vary. Some varieties produce longer thinner fruit and other shorter cylindrical fruit. Some yellow fruiting varieties are prone to green tips. Avoid these if your market does not accept green tip fruits.

What we have learned from our 2018 zucchini variety evaluation – Zucchini fruit grows really fast! Pollination to market maturity only takes about 3 to 4 days. Especially if there is enough moisture in the ground, accompanied by sunny weather and high temperatures. During our evaluation, we harvested Monday, Wednesday and Friday. Therefore, we had a two-day harvest interval during the week and three-day interval over the weekend. Any weather related delays would result in oversized fruit. We aimed to harvest fruit when they reached 6 to 8 inches in length. Fruit that was more than 8 inches long was not acceptable and classified as unmarketable. Our recommendation would be to harvest fruits every day. What we have seen with the two-day harvest interval is that fruit might not be at the required size on that day but will be the next day. It was too big by the time we harvested again. On Mondays, we had many oversized fruits due to the longer harvest interval. Vigorous varieties should be harvested every day. In our evaluation, we have found that the green zucchini varieties Paycheck and Felix produced the highest yield (Table 2). You can expect about 9 lb per plant from these varieties (Table 1). In addition to the marketable yield, Paycheck and Felix produced about 22,000 lb per acre of oversized fruit. If harvested at the appropriate time, the marketable yield of these varieties could have been much higher. The yellow variety ‘Golden Rod’ produced excellent yields of about 90,000 fruit and 30,000 lb per acre (Table 1 & 2). For more information regarding this variety evaluation, download the full report from the 2018 Midwest Variety Trial Report

Table 1: Cumulative yield of ten green and yellow zucchini varieties tested at West Lafayette, IN

Table 2:
Cumulative yield per acre of ten green and yellow zucchini varieties tested at West Lafayette, IN
– Using black plastic mulch will help to control weeds and reduce leaching of fertilizer. A nitrogen side dressing is usually not needed with the use of plastic mulch, but can be applied if needed through the irrigation system. Zucchini has a moderate rooting depth (18-24 inches) and like many Cucurbits does not like to grow in soil that is poorly drained. Raised bed spacing at 6 feet center-to-center with in-row spacing at 18 or 24 inches is ideal. Plant one to two seeds 1 inch deep. Make sure that the soil pH is close to 6.5. The availability of both major and minor nutrients is maximized when soil pH is adequate. Money spent on N, P and K fertilizers will be maximized when the soil pH is optimal. A soil test will be money well spent towards designing a fertility program for your crop. About 75 – 100 lb/acre N is recommended for zucchini. It prefers nitrate nitrogen but can also uptake ammonium nitrogen. A soil test will reveal the levels of phosphorus and potassium and adjustments could be made accordingly. Use guides such as the Midwest Vegetable Production Guide for Commercial Growers, the Nutrient recommendation for Vegetable Crops in Michigan, and the Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota to help you plan and manage your fertility program. The Midwest Vegetable Production Guide is also a valuable source of information for pest and disease management planning. Contact the Purdue Plant and Pest Diagnostic Laboratory (PPDL) if you need assistance with the identification of nutrient deficiencies, pests or diseases.

Harvest – Harvest the immature fruit while the skin is still glossy. Fruit should be ready for harvest 3 to 4 days after the flowers have fully opened. At the time of harvest the fruit weight should be between 0.25 to 0.5 lb. Zucchini pickers should use plastic buckets or solid bottom crates and wear soft gloves to avoid bruises, scratches and fingernail punctures. Cut the zucchini from the plant, leaving about ½ to 1 inch of stem attached to the fruit. To maintain plant vigor, always remove oversized fruit from the plant. Zucchini is usually sold in ½-bushel (21 lb) waxed cardboard cartons on the fresh or wholesale market. Each carton should have uniform and clean fruit, according to the buyers count, length and weight requirements. Ideally, zucchini should be marketed quickly after harvest. Zucchini could be stored for short periods. It is among the most susceptible vegetables to chilling or freezing injury. Pitting is a very common injury symptom. Optimum postharvest storage conditions for zucchini are temperatures between 40 to 45°F and a relative humidity of 95%.

USDA standards – The quality of zucchini and summer squash is often judged largely by appearance and size. The USDA standards for grades of summer squash consist of two criterion. The first (U.S. No. 1) is that stems or portions of the stems be attached to the fruit. The fruit should be fairly young and fairly tender. As defined by the USDA, this means the fruit has reached a desirable stage of maturity, indicated by fairly tender skin and fairly tender undeveloped seeds, and firm, moist seed cavity tissue. The fruit should be fairly well formed, firm, and free from decay or bruises and discolorations. The second (U.S. No. 2) criteria as established by the USDA states that the fruit must be firm, not old and tough, and free from decay or breakdown.

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