Table of contents:
Growing winter onions guarantees that you will be the first to bring onions from your vegetable garden back to the kitchen. Winter onions are fairly large, hardy onions that can withstand low temperatures. The majority of their growth happens after winter, but it is important that the plants establish a good root system before winter. This gives them a 'vegetative head start' compared to the summer onions we plant out in February-March. You can grow winter onions by sowing them, but it is easiest to use plant or onion sets. You can find the varieties available on this website here.
What are winter onion sets?
Winter onion sets are truly a smart choice if you want to enjoy fresh onions from your own vegetable garden early in the spring. By planting these handy onions in the autumn, you can harvest early and won't have to wait long after winter before you can use them in your dishes. In this article, you will learn why winter onion sets are so useful, how to best plant and care for them, and which varieties are perfect for our Dutch climate. This ensures a successful crop and allows you to look forward to a delicious harvest from your own garden in the spring.
Step 1 - Start in time
Start your soil preparation in late summer or autumn. You can start planting your onion sets from August, but most vegetable gardeners wait until October when the weather has cooled down a bit. You can even wait until November, but the ground must not be compacted by frost.
Step 2 - Choose a good spot in the vegetable garden
Choose a sunny spot in the garden. Winter onions are hardy enough to survive difficult weather conditions, but they still prefer to be in the sun.
Step 3: Loosen your soil well
Before you start planting your winter onion sets, it is really useful to take good care of your soil first. Onions love airy, loose soil where their roots can stretch out nicely – just like we like having a little space to feel good! Grab your broadfork or digging fork and loosen the soil to a depth of about 30 cm.
This gives the roots of your onions all the space they need to grow and absorb nutrients. Are you working with heavier clay soil by any chance? Don't worry – just mix some compost or sand into the soil to make it looser and better draining. A little extra love for your soil will eventually lead to strong plants and a delicious harvest you can truly be proud of.
Step 4: Nourish your soil with vinasse potash
To help your winter planting onions grow well, it is best to provide the soil with some extra nutrition. Your onion sets will thank you for it. Vinasse potash or potash is a fine natural fertilizer that is packed with potassium and nitrogen, exactly what your onions need. It ensures that your onions form nice firm bulbs and gives them the strength to get through diseases and the harsh winter well. Simply scatter about 100 grams of potash over 1 square meter and work it well into the top 10 cm of your soil – don't overcomplicate it, just use your hands in the soil. This gives your plants a good start and allows you to enjoy healthy growth and a beautiful, rich harvest in the spring.
Step 5 - Plant your onion sets
Plant each onion set 2.5 to 5 cm deep. In sandy soil, you can plant them slightly deeper than in clay soil. Once you have followed the steps above, you will have loose soil and can plant the onions with their tips just above the surface. Be careful that birds do not mistake those tips for worms, as your onion sets will then be picked out. Insect netting can offer a solution here; when it gets warmer, the netting also protects your onions against the onion fly.
Step 6 - Respect the planting distances for your onions
Place the onion sets 10 to 15 cm apart. If you want larger onions, place them further apart and vice versa. Leave about 30 cm between each row. 30 cm is roughly a shoe size 45. People with smaller feet should probably set their onion rows a few centimeters further apart.
Step 7 - Consider a layer of mulch
Optionally, cover your planting onions with a layer of mulch. This way, water evaporates less and your winter onions will also stay in slightly warmer soil than if you were to leave it bare. Mulch can consist of straw, leaves, compost, and so on.
Step 8 - Watering
Water the onions twice a week during the first 3 weeks. At that point, your onions will already have a root system. After those two weeks, avoid watering, especially if the ground is frozen. Once the ground warms up after the winter, you can bring out your watering can again when you see the soil is hard, cracked, or dry.
Step 9 - Fertilizing (optional)
Give the onions two doses of BIO fertilizer for onions. The first time before a potential frost period (late October - early November). The second time, you fertilize in the spring (April). This will result in thick onions.
Step 10 - Keep your onions weed-free
Keep your onion bed weed-free. For most of the winter onion cultivation period, weeds are not much of a problem; when it is cold, weeds do not grow very fast. However, if you see weeds when the first rays of sun appear, remove them immediately. Weeds compete with the onions for nutrients and water. This results in small, dry onions.
Step 11 - Protect your onions
Watch out for diseases. In the beginning of the cultivation, you will not encounter any problems, but once the soil warms up in the spring, all kinds of fungi and harmful insects become active. Insect netting can offer a solution here starting in March. In the beginning of the cultivation, insect netting also ensures that birds cannot get to the planting material.
Step 12 - Eat the onion greens
You can harvest the greens of onions in the spring once they are 10 cm long. You can cut them with garden shears and use them in all recipes where you would otherwise use onions. Do not cut all the greens off the same onion, however.
Step 13 - Harvest your onions
Harvest the onions as soon as the foliage turns brown; this happens between May and July depending on the weather and the planting time. If the onions grow a seed pod on the foliage before it turns brown, something is going wrong in your cultivation. This phenomenon is a sign that the plant is in panic and wants to reproduce. The reason could be that there is too little nutrition or because the soil has become too compact, preventing the plant from absorbing enough nutrients. Harvest these onions quickly; their flavor diminishes daily. When the foliage dies back and your onions are ready, you can pull them up by the foliage or use a fork to loosen the roots. Remove (unlike with potatoes) as much soil as possible before laying them out to dry. Dry your onions until they develop a dark skin and then store them in a dark, cool place.
Tips
Remove as much skin as possible before storing your onions. The more skin you remove, the drier your onions will become, and the longer they will keep. You could also consider braiding your onions. Hang the onions to dry or dry them on a rack.
What you need to grow winter onions:
Frequently asked questions about growing winter onions:
How deep should you plant winter onions?
Do not plant winter onions too deep. Press the onion set into loose soil with the root side facing down and make sure the tip is just above the ground. In heavy clay soil, the onion set may sit slightly higher to prevent it from getting too wet and rotting.
Are onion sets winter-hardy?
Not all onion sets are equally winter-hardy. Winter onion sets are specifically suitable for planting in the autumn and can tolerate cold temperatures and frost well. Therefore, choose winter-hardy varieties if you want to plant onion sets in the autumn. Also ensure well-draining soil, as winter onions do not like having "wet feet" for long periods.
When can I plant winter onions?
It is best to plant winter onions in the autumn, usually from September through October. Depending on the weather, you can also plant later, as long as the soil is still workable and not frozen. By planting winter onions in the autumn, they can form roots before the winter and continue to grow quickly in the spring.
What can you sow or plant in winter?
Even in winter and late autumn, you can still sow or plant various crops. Think, for example, of winter onions, garlic, and certain types of shallots. Which crops are suitable depends on the month, the weather, and whether you are growing them in open ground, a greenhouse, or a cold frame.
What is the best time to plant onions?
The best time to plant onions depends on the type of onion. You plant winter onions in the autumn, usually in September or October. Summer planting onions go into the ground in the spring, usually starting in March. Those who plant winter onions will benefit from an extra early harvest the following year.
Can I plant an onion from the supermarket?
You can plant an onion from the supermarket if it starts to sprout, but for a reliable harvest, it is better to use onion sets. Supermarket onions are grown for consumption, and their variety and growing characteristics are often unknown. With onion sets that have been specifically selected for the vegetable garden, you have more certainty about growth, hardiness, and the final harvest.
How do you get large onions?
For large onions, it is important that the plants receive enough space, sunlight, water, and nutrients. Plant winter onions in loose, well-draining, and fertile soil and keep enough distance between the onions. Water regularly during dry periods, especially when the bulbs begin to develop. Also, keep the bed as weed-free as possible so the onions do not have to compete for water and nutrients.
