How to Grow, Harvest and Market Onion in Zimbabwe

Winter is coming that means it's time to pick cool-weather crops to grow, harvest and market.

A good option to pick to grow commercially is the onion. Onions are one of the most useful, versatile and popular vegetables. They are used widely in all types of local cooking and are a staple in every household. They also store well which helps reduce post-harvest losses, while giving you extra time to market them.

Local market demand for onions in Zimbabwe is currently not met by domestic production and is usually supplemented by imports from South Africa. There is clearly room to consider adding onions as your main or supplemental winter crop.

We are going to breakdown how to select the right onion type for your climate and location, plant on time, improve your soil and practice good farming practices to get a good and profitable onion crop.

Ready to start onion farming? Let's get started...

Types and Varieties

Fresh-market onions (Allium cepa) come in different bulb shapes (globe, top or spindle-shaped), sizes (small to large) and skin colours (red, white and yellow).

The number one key to growing a good onion crop is selecting the right onion cultivar for your geographic area. Onions are grouped by the number of daylight hours they need to form bulbs.Onion varieties are classified according to their day length requirement: short-day, intermediate-day or long-day length.

Short-day varieties: form bulbs when they receive 10-12 hours of daylight. These varieties are best suited to Zimbabwe because of the short summer days and low latitude of the country. Short-day varieties are usually Grano or Granex types. An example of a short-day variety is 'Texas Early Grano'.

Intermediate-day varieties: form bulbs with 12-14 hours of daylight. They are also known as day-neutral. They need a long growing season but not long days. An example of an intermediate-day variety is 'Candy'.

Long-day varieties: need 14-16 hours of daylight to form bulbs. An example of a long-day variety is 'Walla Walla'.

Onions can also be grouped based on their sulfur content. Pungent varieties contain more sulfur, which makes them keep longer in storage and produce more tears when you cut them. Sweet varieties don't have as much sulfur and need to be used sooner after harvest.

Some recommended varieties for Zimbabwe are:

Short-Day Onions

Texas Early Grano
Yellow Granax (sweet)
Bombay Red (red onion)
Red Creole
Giant Red

Greenleaf Onion

White Lisbon

Site Selection and Soil

Onions prefer an open site with full sun for 6-8 hours a day. They are cool-season plants, whose growth is dependent on the temperature. They like cool weather in the early part of their growth and then warm weather when forming their bulbs. In most areas with mild winters, onions are grown as a winter crop. If you are in a colder area, plant later to stop bolting.Onions typically take from 18-42 weeks from sowing to harvest depending on whether you plant seed or sets.

Soil is another important element for a good onion crop. The ideal soil to grow onions is reasonably fertile, well-drained, rich, loose soil. Onions prefer a soil pH of about 6.0 - 6.8, and will not grow well in acidic or waterlogged soil.

Know your soil pH: before you begin production do a soil test. To do a soil test, first, collect a representative soil sample. See here how to properly collect a soil sample. Send the sample off to your test lab or a local research centre such as Kutsaga Research Board. You will get back an analysis of your soil: its nutrients and pH level: alkaline (high pH), acidic (low pH) or neutral (just right).

To amend your soil pH: After you get your test results you can work on amending or adjusting your soil pH in line with the soil test results. If your soil is too acidic (low pH) you will need to add the recommended lime such as dolomitic limestone to bring it closer to the optimum pH. If it is too alkaline (high pH) you can make it more neutral by adding peat moss, or compost on a regular basis.

Land Preparation

It is best not to grow onions or plants in the onion family (allium) in the same site year after year.The onion family includes garlic, leeks, shallots, scallions, cucumbers, zucchini, summer and winter squashes. Growing plants in the allium family in the same site year after year will cause a disease build up such as nematodes. Plan to rotate your crops to avoid this.

Begin land preparation about a month before planting. To prepare your beds for onion production remove weeds and stones from the fields. Prepare the soil to a fine tilth. Add and dig in a 5-10cm layer of organic matter such as good-quality compost or well-aged manure (4 or more months old) in the last plough. Organic matter will help the soil retain nutrients and moisture.

Make raised beds for planting 100cm wide (standard size), some bed sizes vary. You will be planting multiple rows in the bed. Before planting rake in fertilizer (Compound S) into your beds, at a rate recommended on the package to help encourage root growth and early bulb formation. Cover with 5cm of fresh soil.

Sowing and Planting

Onions can be planted in three ways: as seed, small bulbs called sets, or transplants. Seeds give you a greater selection of varieties, but they take long.

Sets are useful when the growing season is short and are easier to grow.

Sowing onion seeds in trays: Sow seeds in flats or cell packs in February-March, then transplant seedling into the field at least 6-8 weeks before transplanting.

Sowing seed in seedbeds outdoors: To sow seed directly into the ground in areas with long and warm growing seasons. Make sure that you have added well-rotted compost, then an all-purpose fertilizer.

Let's outline the general seed planting steps:

Make seed bed 1m width and 5m in length. Rake soil level to create a smooth layer
To sow onion seeds in place use a string held taut by two pegs knocked into the ground to mark a straight line
Then drag a stake or broom handle and press into the soil to mark out drills (groove) between the pegs into which to sow. Planting in a straight line makes watering and weeding easier after germination
If the bottom of the drill is dry water lightly
Then sprinkle the seed thinly in drills, the seed packet to tell you how deep the drills will be {onion seed are planted shallow approximately 1.2cm deep}.
Cover by carefully drawing soil back to fill the drill, and firm down the soil gently with the back of your rake.
Water well, using a fine spray to avoid dislodging the seed. Sprinkle seed bed with water whenever the surface is dry.
Cover seed bed with a floating row cover (light, woven fabric), this prevents insects getting to your young seedlings.

You can buy unexpired seeds from a reputable supplier like National Tested Seeds.

Sowing onion sets: an onion set is a small onion bulb that is too small to form flowers if subjected to the cold. It has already gone through one bulbing process. Sets produce bulbs faster than starting from seed. They are sold simply as a red, white or yellow onion.

Here are the steps for planting sets:

Make a drill 2cm deep into the ground. To help keep it straight run the edge of a hoe along a length of string held taut by two pegs knocked into the ground.
Plant sets 10cm apart in rows about 30cm apart.
Push each bulb firmly into the soil, burying so only the tip is visible above the soil. Cover with a row cover to deter birds and warm the soil.
Water plants during dry spells, they don't need much water at other times.
Onions take about 18-42 weeks from sowing/planting to harvest using this method.

Onion transplants: transplant is a small plant usually between 8 to 10 weeks old from seeding, that has not yet formed a bulb. They give you a head start on the long onion growing season.Select transplants that look healthy, disease-free and have a neck that has a pencil size in diameter. Pre-irrigate fields before transplanting.

Plant transplants about 2.5 cm deep in wet soil and 8-10cm apart within rows on raised beds 100cm wide, some bed sizes vary. Plant in multiple rows. The number of rows you choose is dependent on your choice of irrigation.

You can buy transplants from a reputable nursery like Emerald Seedlings or Seedridge

Fertilising

Onions are heavy feeders and need constant nourishment to develop big bulbs. Fertiliser application should be based on your soil test. Supplement missing nutrients based on the test. Use fertiliser at the time of planting and add side dressings (extra ration of nutrients) of nitrogen every 2-3 weeks once bulbs start forming. An acre needs about 113kg of nitrogen.

Take care to keep fertiliser away from the foliage and bulbs. Apply near the onion rows, and cover with soil.Water immediately after feeding.

Fertiliser is not needed late into the season especially when necks are soft and tops start to fall over.

You can add organic material to the soil on a regular basis. This can be well-rotted compost or animal manure, both of which contain a good range of nutrients.

Watering

Onion seeds must be kept moist during germination and should not be left to dry out. Watering is critical during the early stages of plant growth when establishing transplants, and when bulbs are forming.

Drip irrigation can help get moisture directly to roots after germination without wetting foliage which can cause powdery mildew.

Keep onions moist with consistent water at a rate of about 1"of water per week. If using drip you will likely water about 2-3 times a week.The rate may vary dependent on your soil, weather, rainfall and plant growth stage.

Onion plants need to be thoroughly watered during dry spells because they have limited root systems. Don't let plants dry out or they may split.

Also don't overwater your onion plants or it will reduce their shelf life. If leaves start to yellow, you may be overwatering.

Stop watering once tops start to fall over and brown and let dry before harvesting. You can use timers and sensors to determine the water needs for your onions.

Weeding

Onions can become easily swamped by weeds especially in their early weeks when the plants are young. Their long growing seasons means they are more opportunities for weed growth. Weed control is important to prevent competition for water, nutrient, and light which reduce bulb formation. Weeds can also harbour pests and disease.

Plan to weed when the weeds are small. Hand-weed while being careful not to cause bulb damage or loosen the bulbs in the soil. Mulch around plants with a thin layer of straw or wood chips to control weeds and retain moisture.

You can also look into registered herbicides to control pre-emergent weeds before you start planting.

{For more on how to control weeds read our 7 tips here}

Problems, Pests, and Disease

Watch out for these problems which may affect your onion leafs and bulbs:

Insects:

Onion thrips: barely visible small insects that appear as tiny yellow or dark specks during hot, dry weather. They cut out the life out of leaves, turning leaves grey and then curling. You can prevent thrips by planting resistant cultivars and keeping beds well-weeded.

Onion maggots: worst onion disease feeding on onion roots and bulbs. Mulching, crop rotation and row covers over newly planted onions can help reduce the risks from these pests.

Nematodes: a variety of nematodes attack onions. Nematodes live in the soil and feed on the root, stems and bulbs of onions. You can prevent nematodes by crop rotation.

Onion Disease:

White onion rot: all in the onion family which includes garlic, leeks and shallots are susceptible to onion rot. Onion rot doesn't occur until the bulbs have been harvested. Practice crop rotation to prevent it.

Downey mildew: a fungal disease that causes yellow spots on the upper part of leaves that eventually show up as mold. It can impair bulb development. Remove and destroy affected leaves, improve air circulation and water at the base to avoid spreading it. It can be prevented by planting in well-drained soil, keeping foliage dry and providing enough space for good circulation.

Purple Blotch: foliar disease. You can use drip irrigation to keep foliage dry.

Bolting: this is the process of premature flowering in onions is called bolting. To prevent bolting choose onion varieties that are suited for your region and planting at the recommended time. Onions bolt when they are planted in the summer in Zimbabwe.

Preventing problems:

If you practice good crop practices you can avoid a lot of diseases and problems.

Here are some good crop husbandry tips:

Choose an onion variety that is well suited to your location. All farming is local!
Practice crop rotation: move onions every year to prevent a build-up of fungal spores.
Buy seeds that are disease resistant from a reputable supplier. If you are buying sets make sure that they are not diseased. Problems can also be reduced by ensuring a good flow of air round your plants by wide spacing.
Pull up and remove infected or problem plants. This will help prevent disease spread.
Maintain weed-free beds. Hand weeding and mulching effectively control most weed species.
Use row covers to push seedlings to produce the most robust plants possible before lengthening days trigger bulb formation.
Keep plants watered and avoid overwatering.
Plant onions in well-drained soil, and avoid overcrowding plants.
Practice good sanitation such as cleaning tools (planting, weeding and harvesting) and washing clothing after use
Use chemical controls only as a last resort.

Harvesting & Storing Onions

When to harvest onions: harvest onions when they reach optimum maturity. You can determine maturity by pinching the onion neck. Immature onions have stiff necks, whereas mature necks are soft and limber.

Another way to tell that onions plants are ready for harvesting is when 50% of plant leaves fall over and die back. Stop irrigation at this point. Harvest before the foliage dries completely. To harvest carefully loosen the bulbs from the soil using a garden fork or by hand and pull the bulb out by its neck. Be careful to avoid bruising or damaging bulbs.

Lay the bulbs on top of the ground for a few days to dry out in the sun. Keep the onions from getting sunscald by placing the tops of one row over the bulbs of another row. Onions are cured when their tops are thoroughly dry. Once the outer skins are thoroughly dry gently knock off any loose soil and remove the tops.

If rain is expected cure under cover. Place onion bulbs with tops in a cool, dry well-ventilated shed to 2-3 weeks to cure. After curing cut the tops about 1 inch from the bulbs and store the bulbs in a cold, dry, and airy place. Handle with care to avoid bruising.

Short-day varieties, when harvested carefully, can keep for several weeks or longer, this depends on the storage conditions.

Storing: Store dried bulbs in netting or orange mesh bags to permit airflow. Place the onions in a cool, dry shed or area with good ventilation. Handle them with care and avoid dropping them or you can cause bruising and damage. The optimal temperature for onion storage is 0 degrees C and 60-70% humidity. Maintain good sanitation, cool temperatures and humidity in the storage room to prevent or reduce post-harvest losses.

Marketing

You can sell fresh onions at a fresh market like Mbare Musika. Market prices fresh markets fluctuate based on the supply and demand on the market.

Monitor the market prices for the current price to avoid selling your onions too low at the market or to middlemen.

You can also sell your onions wholesale or to retail supermarkets such as Pick n Pay for fresh consumption.Other marketing avenues: restaurants, food service, schools, and hospitals. Start talking to buyers to see their buying needs.

Other buyers of onions are processors. They buy onions for processing into seasonings, sauces, and soup. You may need to meet their volume requirements, but this can be met by pooling your supply with other onion farmers.You can also sell your onions directly to customers out of the back of a pickup truck at a roadside. Other options are selling on classifieds. Be creative!

Recordkeeping

Record what you planted and when, and how your onions performed and yields. Also, make a note of the inputs you used: how much and when you applied them. These include seed, fertiliser, labour, irrigation, crop protection, harvesting and storing costs. Keep track of any problems you faced and what solutions you applied. This will help with next year's crop and with deciding whether to plant onions again. You can use a simple notebook or a free app like Evernote to keep tracks of your farm records.

At the end of the season spend some time reviewing your notes. Consider what you could have done slightly differently. Also, think about what went right. It's not always about the negative!

Conclusion

A good onion cultivar for your region, loose, well-drained soil, fertilising and watering are all important things for a good onion crop.

If you build your soil and practice good crop husbandry you will likely benefit from giving onion growing a try. Happy farming!

If you have any questions, tips or feedback add them in the comments.

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