Disclaimer Check with your certifier or the Organic Materials Review Institute (OMRI) that any products mentioned here are included in the OMRI list of approved products, as the list of approved products changes annually. Also, follow all label instructions carefully when using any product. Mention of a product does not imply endorsement by USDA, the SARE program, or the author. Exclusion does not imply a negative evaluation.
Soil preparation
Summer squash should not follow after other cucurbits or nightshades, but it follows well after cole crops and leguminous green manures or sweet corn.
Where Phytophthora (Phytophthora capsici) is an issue, rotate away from this land. Biofumigation has shown some effectiveness to reduce incidences.
Apply compost and other amendments based on the results of a soil test.
Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
Incorporate compost and plant summer squash in raised beds covered with or without plastic mulch.
Common recommended fertilizer rates1
Nitrogen
Phosphorus
Potassium
pH
100
0-160
0-160
6.0-6.4
1Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York.
Dunja, Spineless Perfection and Green Machine are popular among organic growers. Multipick, Slickpick and Smooth Operator are popular as summer squash varieties.
Greenhouse guidelines
EZ Seeder seeding plate #5
Early in the season, germinate seeds in a germination chamber unless you can keep the greenhouse warm both day and night. Germination improves greatly at optimum temperatures.
Use a 1020 tray with 24 pots for more light, resulting in stockier plants. When using a 38-pot tray, make sure you transplant before they get leggy.
Cell pack tray
Germination temp
Growth temp
Hardening off
Notes
24 or 38
75°
75°
Withhold water
Put plug trays on a wire mesh bench to encourage air pruning. Take outside 1 week before planting in the field.
Number of successions
Seed summer squash and zucchini 3 weeks before you transplant in the field. If you aren’t able to maintain a healthy plant throughout the summer, repeat another planting after about a month. Plants will start to drop productivity due to a lack of nutrients and increased disease and insect pressure.
Signs to watch for and what to do
Summer squash grows fast. Make sure plants can go in the field without becoming leggy because leggy plants suffer and can perish in the summer heat.
Harden plants off outside; plants that are lush don’t perform well in the field.
Transplant in the field when plants have enough of a root ball to hold the soil in the pot or cell pack together. When they can’t, their roots will be damaged and the plants have a higher fatality rate.
Transplanting tips (when using plastic mulch)
Avoid laying plastic mulch after crops that leave a lot of residue on the surface, such as cabbage or corn stalks. When establishing an early cover crop of oats and peas before plasticulture, mow it before the winter to avoid clogging up the plastic mulch layer in the spring.
For the first planting, use infrared transmitting (IRT) plastic because it helps warm the soil.
Lay plastic mulch at least a week before planting to allow weed seeds to germinate and the soil to warm. Planting on the same day as laying the plastic will cause weed pressure in the planting hole.
Avoid transplanting in plastic mulch during the heat of a hot summer day. The heat of the plastic can cause damage to the young seedlings. To avoid burning the young plants, transplant in the evening, use stocky transplants and water deeply. If planting by hand, water plants with a watering can. Avoid applying row covers in hot conditions. When hot weather is expected after transplanting, only use insect cover for protection.
To help resist striped cucumber beetle damage, dissolve Kaolin clay (as in Surround) in plenty of water and drench the complete tray in the solution before transplanting.
The following tip is useful when you have harvest lanes, where every 8 or 10 beds are separated by a grass strip: Mark a 4-foot “walking break” on the plastic mulch every hundred feet and don’t plant anything in that 4-foot strip. This will make harvesting easier by allowing you to easily pass through the crop when removing buckets. Instead of carrying the buckets of squash to the headland, one can walk through the crop (instead of over) to the left or right and place the buckets in the harvest lane to be collected by truck or other vehicle.
Water wheel planter
Rows
In-row spacing
Planting depth (inches)
Notes
1
12 inches
Same level as the potting medium
Add kelp to water as a 0.5% solution in the water wheel planter.
Cultivation procedures (without plasticulture)
If growing squash in the traditional bed system, you can use your regular cultivation setup with side knives reconfigured for a one-row system. Don’t use any finger weeders. Precision cultivation can damage cucurbits, so keep a good distance from the crop to avoid damage.
Hand hoe between plants.
Cultivation procedures (with plasticulture)
After transplanting, cultivate once or twice between plastic with a rolling cultivator or Spyder. Cover the wheel tracks with rye straw at a rate of 3 lbs. per foot. (One 600 lb. round bale covers 200 feet of wheel track.) Increase this amount when using an early cutting of orchard grass, because hay breaks down much faster than straw. Over time, hay and straw mulch will release a significant amount of K and other beneficial properties like silicon, contributing to long-term soil health. Mulching also protects crops from soil splashing. This reduces soilborne diseases and time spent cleaning produce after harvest.
Frost, disease and insect protection
Plant early plantings downwind from later varieties, as both powdery and downy mildew are windborne.
For your earliest plantings, use floating row covers to protect against frost and striped cucumber beetles. For varieties that require pollination, remove the covers at flowering. Use 10-gauge wire to support the row cover, since abrasion against the cover will damage the plants. If you don’t need frost protection or a warm environment, you can use the longer-lasting insect covers to provide protection against beetles.
Squash bug populations can be kept under control by rotating far from where you grew squash the previous year. Unfortunately, squash bugs shelter in the straw that’s between plastic mulch.
Powdery mildew: The best way to avoid losses from powdery mildew is to use tolerant or resistant varieties. Powdery mildew can be somewhat controlled with a mixture of Bacillus subtilis, as in CEASE, and potassium bicarbonate, as in MilStop SP. Sulfur causes phytotoxicity in squash, so be careful if you’re applying sulfur in any form to control powdery mildew. Also, consider using tolerant or resistant varieties.
Downy mildew can be somewhat controlled with the biological control Pseudomonas aeruginosa, as in Zonix. Also, consider using tolerant or resistant varieties.
A full list of OMRI-listed control products on cucurbits, along with their efficacy, is available from CALS.
Other cultural practices
Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop.
Double cropping and/or cover cropping
Incorporate any remaining plants, weeds and fruit into the soil, and plant a cover crop like rye and vetch. This will reduce the squash bug population.
If weed pressure was high and caused a lot of seed rain, it’s better to refrain from any fall tillage. Instead, allow the weed seeds to decay and be eaten by birds and rodents over the winter months to reduce future weed pressure. Unfortunately, this is contradictory to keeping the squash bug population under control.
Production, Winter Squash
Cucurbita pepo (Acorn, Spaghetti, Delicata)
Cucurbita maxima (Kabocha, Hubbard)
Cucurbita moschata (Butternut)
(Cucurbiticeae or cucumber family)
Soil preparation
Winter squash should not follow after other cucurbits or nightshades, but it follows well after cole crops and leguminous green manure or sweet corn.
Where Phytophthora (Phytophthora capsici) is an issue, rotate away from this land. Biofumigation has shown some effectiveness to reduce incidences.
Apply compost and other amendments based on the results of a soil test.
Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
Incorporate compost and plant winter squash in raised beds or on flat ground, with or without plastic mulch.
Common recommended fertilizer rates1
Nitrogen
Phosphorus
Potassium
pH
100
0-160
0-160
6.0-6.4
1Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York.
Honeynut, Delicata, Bon Bon, Chieftain butternut, Royal Ace acorn, Sunshine, Red Kuri, Baby butternut, and Spaghetti are popular winter squash varieties amongst growers.
Greenhouse guidelines
EZ Seeder seeding plate #5 or seeded by hand
Use a 1020 tray with 24 potsfor more light, which results in stockier plants. When using a 38-pot tray, make sure you transplant before they get leggy.
Cell pack tray
Germination temp
Growth temp
Hardening off
Notes
24 or 28
75°
75°
Withhold water
Put plug trays on a wire mesh bench to encourage air pruning. Take outside 1 week before planting in the field.
Signs to watch for and what to do
Winter squash grows fast. Make sure to transplant into the field before they get leggy.
Transplant readiness indicators
Harden plants off outside; plants that are lush don’t perform well in the field.
Transplant in the field when plants have enough of a root ball to hold the soil in the pot or cell pack together. When they can’t, their roots will be damaged and the plants have a higher fatality rate.
Transplanting tips
Lay plastic mulch at least 1 week before planting to allow weed seeds to germinate and the soil to warm. Planting on the same day as laying the plastic will cause weed pressure in the planting hole.
Avoid transplanting in plastic mulch during the heat of a hot summer day. The heat of the plastic can cause damage to the young seedlings. To avoid burning the young plants, transplant in the evening, use stocky transplants and water deeply. If planting by hand, water plants with a watering can. Avoid applying row covers in hot conditions. When hot weather is expected after transplanting, only use insect cover for protection.
To help resist cucumber beetle damage, dissolve Kaolin clay (as in Surround) in plenty of water and drench the complete tray in the solution before transplanting.
Water wheel planter
Rows
In-row spacing
Planting depth (inches)
Notes
1
12 inches
Same level as potting medium
Add kelp to water as a 0.5% solution in the water wheel planter.
Direct seeding information
Seeder
Rows
Seeds per foot
Seed plate no.
Depth (inches)
Sprocket setting
Notes
MaterMacc
1
1
9 H 4.5
1/2
22-18
Cultivation procedures (without plasticulture)
If you didn’t plant winter squash through plastic mulch, eliminate weeds when they’re in the white thread stage. The choice of tools depends on row distance.
You can use your regular cultivation setup with side knives if growing squash in the traditional bed system. Don’t use any finger weeders. Precision cultivation can damage cucurbits. Keep some distance from the plants to avoid this.
You can use a regular field cultivator and drive between rows if you planted the squash 10–12 feet apart.
In both cases, hand hoe between plants.
Cultivation procedures (with plasticulture)
After transplanting, cultivate once or twice between plastic with a rolling cultivator or Spyder. Cover the wheel tracks with rye straw at a rate of 3 lbs. per foot. (One 600 lb. round bale covers 200 feet of wheel track.) Increase this amount when using an early cutting of orchard grass because hay breaks down much faster than straw. Over time, hay and straw mulch will release a significant amount of K and other beneficial properties like silicon, contributing to long-term soil health. Mulching also protects crops from soil splashing. This reduces soilborne diseases and time spent cleaning produce after harvest.
Frost, disease and insect protection
Plant early plantings downwind from later varieties, as both powdery and downy mildew are windborne.
For your earliest plantings, use floating row covers to protect against frost and striped cucumber beetles. For varieties that require pollination, remove the covers at flowering. Use 10-gauge wire to support the row cover, since abrasion against the cover will damage the plants. If you don’t need frost protection or a warm environment, you can use the longer-lasting insect covers to provide protection against beetles.
Squash bug populations can be kept under control by rotating far from where you grew squash the previous year. Unfortunately, squash bugs shelter in the straw that’s between plastic mulch.
Powdery mildew: The best way to avoid losses from powdery mildew is to use tolerant or resistant varieties. Powdery mildew can be somewhat controlled with a mixture of Bacillus subtilis, as in CEASE, and potassium bicarbonate, as in MilStop SP. Sulfur causes phytotoxicity in squash, so be careful if you’re applying sulfur in any form to control powdery mildew. Also, consider using tolerant or resistant varieties.
Downy mildew can be somewhat controlled with the biological control Pseudomonas aeruginosa, as in Zonix. Also, consider using tolerant or resistant varieties.
Where Phytophthora (Phytophthora capsici) is an issue, rotate away from this land. Biofumigation has shown some effectiveness to reduce incidences.
A full list of OMRI-listed control products on cucurbits, along with their efficacy, is available from CALS.
Other cultural practices
Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop.
Double cropping and/or cover cropping
Incorporate any remaining plants, weeds and fruit into the soil, and plant a cover crop like rye and vetch. This will reduce the squash bug population.
If weed pressure was high and caused a lot of seed rain, it’s better to refrain from any fall tillage. Allow the weed seeds to decay and be eaten by birds and rodents over the winter months to reduce future weed pressure. Unfortunately, this is contradictory to keeping squash bug populations under control.
An average of 4.33 lbs. of marketable zucchini per row foot, but higher numbers are possible with good fertility management, optimum irrigation and good insect control practices.
Standards
Harvesting1 5–6 buckets or 120 lbs. per person, per hour
Tools and supplies needed
Pocket or paring knives, ⅝-bushel buckets
1Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.
Ready-to-harvest and quality indicators
Yellow squash is 4–6 inches long and has a good thickness. Generally, harvest zucchini at a length of up to 7–8 inches with a thickness of 1 ¼–1 ¾ inches.
On warm days, pick squash every day, and sometimes twice a day, to control the size you’re harvesting.
Fruit is straight (apart from crookneck types), firm from stem to tip and free from defects. Discard squash with soft tips. Misshapen squash indicates poor pollination.
Plants with squash bug infestations need to be abandoned and worked under to avoid spreading to later successions.
Harvest procedures
Wash hands and sanitize knives before harvesting squash.
You need to harvest squash and zucchini from both sides of the plant to avoid misses.
Zucchini needs to be cut from the plant, and while you can also cut summer squash, try to twist it off by hand without damaging the plant. The advantage of this is that viruses won’t be transmitted between plants via the harvest knife.
Protect the fruit from being damaged by the spines of the plant by wrapping your hand around the fruit, and carefully place it in the bucket. Many harvest crews will wear gloves to avoid damaging the tender fruit with their fingernails.
When the bucket is full, carefully put it next to the harvest lane.
If the vines give you a rash, wear a long-sleeved shirt.
After harvesting all of the squash and zucchini, pick up buckets with a harvest truck or wagon.
Count into boxes in the pack shed.
Washing procedures
Using adequate mulch like straw can keep the fruit clean, which makes washing unnecessary. Sort and pack squash in a well-lit packing shed. Many blemishes are discovered during this process.
If washing is necessary, use a rinse conveyor washer or use a brusher washer. Add a sanitizer like hydrogen peroxide and peracetic acid to the water in the circulation tank of the rinse conveyor vegetable washer. Use the guide How to Wash Produce Using a Peracetic Acid Solution to establish how much sanitizer solution to add to water. Make sure you use the appropriate pressure on the nozzles to avoid crop damage.
Under no circumstance should you dunk squash in cold water, as this can create cross-contamination of pathogens that are absorbed through the skin of the fruit.
Packing and storage summary for summer squash and zucchini
Packing in the field
Fill buckets
Packing for delivery
40–60 pieces per 1 ⅑-bushel box, or half that amount when packed in a ½-bushel box. See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops.
Storage
Chilling injury is caused when summer squash is kept at temperatures below 41° for more than a day or two. For 1–2 weeks of storage, keep squash at 41–50° and 95% humidity. Zucchini is sensitive to ethylene exposure, which will cause it to soften and turn color. Allow for good air exchange and don’t store zucchini with crops that release ethylene.
Harvest, Winter Squash
Yield
Yields of marketable winter squash per row foot vary greatly depending on the variety, insect control and season. Butternut yields are double that of many of the buttercups and Japanese types. Expect anywhere between 1.5 lbs. and 3 lbs. per row foot.
Standards
Harvesting1 400–600 lbs. per person, per hour when loading into a 20-bushel bin
Washing 400–600 lbs. per person per hour when using a brusher washer
Tools and supplies needed
⅝-bushel buckets, a tractor with a forklift, and 20-bushel bins
1Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.
Ready-to-harvest and quality indicators
Squash have full color, which varies based on the variety. Green acorn squash develops an orange ground spot. Harvest kabocha squash when they’re slightly on the green side, as they continue to mature after harvest.
Squash are mature and are free of blemishes and black rot infestations (on butternut squash, this looks like concentric circles).
Harvest procedures
Harvest squash before nighttime temperatures drop into the 40s if possible, as these temperatures can cause chilling injury, which accumulates over time.
The harvest crew goes down the rows and pulls the squash off the vines. Cut stems on acorn and butternut very short so they don’t puncture other squash in the bin.
Put each variety of squash in a windrow down the length of the bed (out of the vines so they are easy to see), or you can put them directly into buckets.
It’s time to pick up the squash when there is a good amount of one variety harvested.
One person rides in a bulk bin and another person hands them the squash until the bin is full enough for both people to gently fill from outside the bin. Or, carefully empty the buckets into the bulk bin.
Each variety of squash should have its own bin.
Butternut and buttercup squash need to be cured in the greenhouse at 85° for 7–10 days to be sweet tasting. Cover the greenhouse with 80% shade cloth. Other varieties don’t need to be cured.
Washing procedures
Wash squash in a rinse conveyor washer or brusher washer just before delivery.
Squash is sorted for quality and size.
To dry them, put 2 fans blowing at high speed towards the pallets of washed squash.
For a CSA delivery, distribute sweet dumpling, delicata squash, buttercup and kabocha varieties first, as they don’t keep very long. Keep butternut for the last deliveries.
To avoid chilling injury, don't store winter squash below 50° or otherwise expose it to a temperature this low. The best temperature for long-term butternut squash storage is 59°. Winter squash is moderately sensitive to ethylene exposure, which will cause it to soften and turn color. Allow for good air exchange and don’t store winter squash with crops that release ethylene.
This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through the Sustainable Agriculture Research and Education (SARE) program. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.
