Allium cepa (Alliaceae or onion family)
Production
Soil preparation
- Onions should not follow other members of the allium family. Also, plant onions away from garlic due to the presence of overwintering thrips.
- Total nutrient uptake is 145 lbs. of N, 25 lbs. of P and 155 lbs. of K.
- 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.
- Most vegetable crops remove little P, but at times your soil test result will call for additional P. Unfortunately, there aren’t short-term options for an organic grower to increase the available P levels in the soil. Through the use of animal-based fertilizers, P will build up to a level in the soil that is sufficient for all vegetable crops.
- A fertilizer company can add OMRI-listed potassium sulfate to compost if it doesn’t have enough K to meet the crop’s needs. If this isn’t possible, spread the correct amount of fertilizer and incorporate it before planting.
- Incorporate compost and amendments and plant onions in raised beds.
Common recommended fertilizer rates1
| Nitrogen | Phosphorus | Potassium | pH |
| 120 | 0-200 | 0-200 | 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. | |||
Varieties
Greenhouse guidelines
- EZ Seeder seeding plate #16
- Since onions are started 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.
| Cell pack tray | Germination temp | Growth temp | Hardening off | Notes |
| 72, 98 or 128 | 60°–85° | 60°–65° daytime; 55°–60° nighttime | Withhold water | Sow 3–4 seeds per cell. Put plug trays on a wire mesh bench to encourage air pruning. Take plants outside 1 week before planting in the field. |
| 128 | 60°–85° | 60°–65° daytime; 55°–60° nighttime | Withhold water | Sow 1 seed per cell. Put plug trays on a wire mesh bench to encourage air pruning. Take plants outside 1 week before planting in the field. |
Transplant tips
- While it’s a personal choice to plant onions in a clump or as individual transplants, what matters most is that onions cannot be given too much space in the field. While onions planted at low populations become quite large, the incidence of bacterial rot is much higher, leading to crop loss.
Signs to watch for and what to do
- Onions take a considerable amount of time from seeding to transplanting. Over time, nutrients in the small cell are used up or leached out from overwatering. If you notice nutrient deficiency or poor growth, feed with an OMRI-listed liquid fertilizer.
- Clip tops off tall onion leaves to avoid falling over. Transplant after a good “haircut.”
Transplant readiness indicators
- Transplant in the field when plants have enough of a root ball to hold the pot together.
Transplant tips
- Mix Streptomyces lydicus, as in the product Actinovate SP, and/or an extract of giant knotweed, as in the product Regalia, in a water solution. Drench the complete tray before transplanting. This prevents many soil- and foliar-borne pathogens, and builds immunity against them. Wear protective clothing and gloves when handling these products.
- Planting in plastic mulch can increase onion yield in multiple ways. The higher soil temperature in April and May results in bigger onions. Drip irrigation along with the mulch improves soil moisture. Additionally, you can apply a silver strip to the plastic to repel thrips away from the onions.
Water wheel transplanter
| Rows | In-row spacing | Planting depth (inches) | Notes |
| 3-5 | individual plants: 4 inches; clumps: 9 inches | Don’t plant onions too deep in the planting holes, as they could slip underneath the plastic mulch | Use water generously when using the water wheel planter. |
Cultivation procedures
- 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
- Watch for onion thrips, and control with a spinosyn-based product, such as Entrust, or Beauveria bassiana, as in the product Mycotrol ESO. With Beauveria bassiana you’ll see results after a week of applying. Alternatively, use a mineral oil like JMS Stylet-Oil. Repeat applications of the selected product every 5–7 days. Don’t exceed the maximum rate of 3 applications per season for Entrust. As direct contact with the pest is required for all these products, only spray at night, as thrips are nocturnal. Act when pest pressure is still low.
- Check for allium leaf miners. As this pest will emerge over several generations, follow local Extension guidance on when to use exclusion netting to avoid an infestation.
- Botrytis leaf blight (fungus), Xanthomonas leaf blight (bacterial) and downy mildew (Peronospona destructor, a fungus) are all problems you can avoid with long rotations, good sanitation (removing or incorporating diseased plant material), certified-disease-free seed (or hot water treatment) and good water management.
- Purple blotch (Alternaria porri) occurs mostly in the summer under wet and humid conditions. Plants that are weakened by thrips are more susceptible to this disease. Keeping the crop weed free to allow for air circulation, planting long rotations, practicing good sanitation (e.g., removing or incorporating diseased plant material), and avoiding excessive N are good preventive measures.
- Many bacterial bulb diseases develop between pre-harvest and storage. Tips for controlling this disease:
- Avoid damage to onions during harvest. Prematurely topping onions can cause them to contract bacterial bulb diseases. If topping is necessary, wait until 90% of tops have lodged and leave at least 4 inches of stem above the bulb.
- A late release of nitrogen from a generous compost application, and/or a low onion population per square foot results in higher disease pressure.
- Excessive moisture combined with high temperatures also causes higher disease pressure. Avoid using overhead irrigation late in the season.
- Harvest when onions are mature, which is when 90% of the leaves have lodged.
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.
- When onions are starting to lodge, hold back on irrigation to avoid bacterial rot. Also, make sure that plastic mulch isn’t touching the onions. Open the holes as wide as possible to avoid burn damage. While soil warming is a benefit of plastic mulch early on, at this point it can become a liability as the leaves no longer shade the plastic. Removing the mulch is an option, but take great care not to damage the onions.
Cover cropping and/or double cropping
- After the last harvest, remove plastic mulch and drip tape. Work under any plant remains to avoid insect or pathogen buildup and plant a cover crop. In the northern United States and Canada, you can plant oats and peas after onions, or rye and vetch at later dates. Adjust accordingly in other regions.
Production, High Tunnel (Overwintering)
Soil preparation
- Incorporate compost or leave it on the soil surface. Plant onion sets in raised beds.
- Total nutrient uptake is 145 lbs. of N, 25 lbs. of P and 155 lbs. of K.
- Apply compost and other amendments based on the results of a soil test.
- A fertilizer company can add OMRI-listed potassium sulfate to compost if it doesn’t have enough K to meet the crop’s needs. If this isn’t possible, spread the correct amount of fertilizer and incorporate it before planting.
Common recommended fertilizer rates1
| Nitrogen | Phosphorus | Potassium | pH |
| 120 | 0-200 | 0-200 | 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. | |||
Varieties
Planting information
- Plant onion sets around September in an 8x8 inch grid.
| Rows | Distance | Planting Depth | Notes |
| 5–6 | 8 inches | Plant onion sets just below the surface like garlic. | Cover onions with mulch or a thin layer of compost and add sufficient moisture to the soil to get them through the winter. |
Frost, disease and insect protection
- Because you’re growing these onions in a high tunnel over the winter, you won’t have any pest issues aside from any pests already living in the tunnel. Apply good sanitation in the tunnel by removing old plant material.
Other comments
- Onions are ready to harvest starting in June in the Northeast. Adjust harvest and planting dates according to your region.
Harvest, Onions With Green Tops
| Yield | An average between 0.8–1 bunch per row foot |
| Standards | Harvesting1 40–60 bunches per person, per hour |
| Washing 80–100 bunches per person per hour | |
| Tools and supplies needed | 1 ¾-bushel plastic box, rubber bands or twist ties (customer preference may influence this), and knives |
| 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
- Harvesting onions with tops allows for CSA and farmers market growers in the Northeast and Midwest to bring onions to their customers in June. Cured storage onions are ready for market by mid-August and can also be harvested fresh (without tops) in July.
- Onions are 2–4 inches in size.
- Onion bulbs are firm and have no signs of any defects from insects, bacterial rot or other pathogens.
- Leaves are light to deep green, are not crushed or damaged, and have no signs of any defects.
Harvest procedures
- Wash hands and sanitize knives before harvesting.
- The first person pulls onions out by grabbing them as low as possible at the stem to avoid crushing the green stems. Place the onions on top of the bed all facing the same way.
- The second person cleans off the outer leaves around the bulb, which results in a clean, white bulb.
- The third person bunches 3–4 onions together with twist ties or rubber bands.
- The fourth person cuts the excess length off the leaves to allow the bunch to fit lengthwise in a box.
- The last person picks up the finished bunches, counts them and places them in the boxes.
Washing procedures
- Fresh, bunched onions look much nicer when clean. If washing is necessary, wash your hands and place green onions on a wire mesh table and rinse them off with a spray nozzle. Don’t dump them into a washing tub, as submerged onions will decay quickly by absorbing water into their leaves.
- Alternatively, run green onions through a rinse conveyor washer, and make sure you use the appropriate pressure on the nozzles to avoid crop damage. 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.
Additional resources
Packing and storage summary for onions with green tops
| Packing in the field | 15 bunches in a regular 1 ⅓-bushel box |
| Packing for delivery | 24 bunches in a regular 1 ¾-bushel box or 12 bunches in a 1 ⅑-bushel box. See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops. |
| Storage | 32°–41° and 95–100% humidity. Pack in closed containers for storage longer than a week. |
Harvest, Storage Onions
| Yield | An average of 1.5 lbs. of marketable cured onions per row foot |
| Standards | Harvesting1 175 lbs. per person, per hour, or approximately 200 hours per acre. This includes pulling the onions, removing the tops and putting them into boxes. |
| Curing, cleaning and sorting 250 lbs. per person, per hour | |
| Tools and supplies needed | ⅝-bushel buckets or regular 1⅓-bushel boxes, and knives |
| 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
- Reduce irrigation when onions start to mature (about 3 weeks before harvest) to maintain a healthy crop. Organic farmers don’t have many tools to control the N levels of their soil, as most N is released from biological sources. A high N level, high thrips feeding, low plant population (wide spacing) and excessive irrigation all contribute to bacterial bulb decay and especially bacterial internal soft rot. Reducing irrigation water reduces N uptake.
- Onions are almost ready to pull when the plants stop putting on new leaves, the necks get soft and plants start to fall over, and the roots begin to die. Generally, it’s said that onions are ready when 75% of the plants have lodged, but it pays to leave them in the ground until the roots are loose as well. They continue to put on size even when the leaves have fully lodged.
- Pull on plants and see how hard it is to pull them out of the ground. If you don’t feel much resistance, they’re ready to harvest.
- Onions should be firm, have a good bulb size, and contain no defects from insect damage, sunscald, or bruising. Onions should also have good internal condition with no presence of bacterial bulb decay.
Harvest procedures
- To avoid sunscald, don’t harvest on hot days when the temperature will soar into the high 80s or 90s. To avoid black mold, don’t harvest in the rain or on days when the relative humidity is higher than 90%.
- Pull onions out of the ground, place them in windrows and orient the leaves so they protect the bulbs from direct sunlight. Ensure onions aren’t injured, because this can lead to the postharvest development of pathogens.
- Conduct field curing when temperatures are at least 75° but lower than 90°. When conditions are ideal, this can take a few days to a few weeks. However, this is always a risky proposition on the East Coast, where the weather is easily changeable. Also, when you do field curing, you want to make sure that the onions are fully mature and have developed a solid outer wrapper. When onions prematurely lodge due to high thrips pressure, they have not developed enough of a wrapper to protect them against sunscald. When you feel confident about the quality of the onions and the weather forecast, follow the following procedures:
- Windrow the onions and allow them to dry in the field.
- Alternatively place the onions in wooden boxes that provide plenty of ventilation. Only place a small layer of onions in each box and stack the boxes on top of each other. In case it does rain you will be able to provide some protection with a tarp.
- When temperatures are high or onions have prematurely lodged, avoid long-term field curing and bring onions into a barn or high tunnel within a few hours of pulling. Expose onions to temperatures of up to 86°F and an optimum relative humidity of 75–80%. You can cut the tops of the onions, but leave approximately 4 inches of stem. Cutting the onions lower can introduce bacterial soft rot. Lay the onions out in single layers and avoid stacking them on top of each other. Ensure good air movement. (Forced air curing with a plenum allows for higher curing temperatures.)
- If stored in a plastic tunnel, cover the tunnel with 60% shade cloth to protect the onions from sunscald.
- Curing in a plastic tunnel or well-ventilated barn can take up to 2–3 weeks depending on the weather and storage conditions. When you can no longer roll any stems between your fingers and the stem tissue feels like paper, onions are cured and you can bring them into long-term storage.
- Store onions at close to 32° and 65–70% humidity for long-term storage.
Additional resources
Packing and storage summary for storage onions
| Packing in the field | ⅝-bushel buckets |
| Packing for delivery | Pack in regular 1⅑-bushel boxes or mesh bags, 40 lbs. total, sorted by size (smaller than 3 inches or larger than 3 inches). See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops. |
| Storage | At 32°–41° and 65–70% humidity. Onions are moderately sensitive to ethylene exposure during long-term storage. |
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.