Growing onions and leeks during winter can be tricky if you live in a cold region. But what if you could control the temperature and humidity levels around your plants without relying on artificial heat sources? A cold frame is a perfect solution! It is an outdoor structure that uses solar energy to keep the temperature warm and the humidity high, creating an ideal environment for growing plants even in the winter. In this blog post, we’ll show you how to grow onions and leeks in a cold frame this winter, so you can enjoy fresh, homegrown produce all year round.
Just click here to read my post on building your own Cold Frame, along with different materials you can use from wood, PVC, cement blocks or wooden pallets!
Optimum Location for Cold Frame
Selecting the right location for your cold frame is critical for the successful cultivation of onions and leeks. Ideally, it should be situated in a south-facing, sunny spot in your garden to maximize exposure to sunlight. This will ensure that the cold frame captures as much solar heat as possible during the day. Make sure there’s good drainage to prevent water from pooling around the base, which could lead to rot. Also, try to choose a location that is sheltered from strong winds, which can lower the internal temperature of the cold frame and potentially damage the plants. Remember, the goal is to provide a warm, humid environment for your onions and leeks to thrive during the winter months.
Best Type of Onions and Leeks for Winter Gardening
Choosing the right variety of onions and leeks for winter gardening can mean the difference between success and frustration. For onions, overwintering varieties such as ‘Senshyu Yellow’, ‘Electric’, and ‘Shakespeare’ are recommended for their ability to withstand winter conditions. These hardy types start growing in the fall and continue their growth in early spring, yielding a harvest by mid-summer.
Leeks, on the other hand, are naturally hardy and can tolerate colder conditions. Winter varieties like ‘Musselburgh’ and ‘Blue Solaise’ are particularly robust, becoming sweeter after exposure to frost. These leeks can be harvested throughout winter and into early spring, providing a continuous supply of fresh vegetables during the colder months. Be sure to choose these varieties for your cold frame to ensure a successful harvest.
Preparing the Soil for Ground and Pot Planting
When planting onions and leeks, soil preparation is key. Whether you’re planting in the ground or in pots, aim for a loose and well-draining soil mix rich in organic matter. For ground planting, turn over the soil to a depth of about 12 inches. Add compost or well-rotted manure to improve fertility and drainage. Break up any soil clumps and remove any debris, like stones or roots, to create a fine tilth.
For pot planting, choose a high-quality potting mix, preferably one designed for vegetables. You can also make your own mix by combining equal parts of compost, garden soil, and coarse sand or perlite. Make sure your pots have good drainage holes and are large enough to accommodate the full-grown plants. Remember, leeks require deep pots because of their extensive root system and high moisture needs.
In both cases, a pH level of 6.0 to 7.0 is optimal. Soil acidity can be adjusted with lime (to raise pH) or sulphur (to lower pH) as necessary. Providing the right soil conditions will help your winter onions and leeks to establish quickly and grow strongly, optimizing their potential to produce a bountiful harvest.
When to Plant Onions and Leeks for Winter Harvest
Timing is crucial when planting onions and leeks for a winter harvest. The best time to plant overwintering onion varieties is in late summer or early autumn. Specifically, late August to mid-September is ideal for most regions. This allows the plants enough time to establish a strong root system before the winter.
On the other hand, leeks should be planted a bit earlier, from late spring to early summer. This gives them ample time to mature before winter. Some winter varieties of leeks can even be planted as late as early autumn for a late spring harvest.
Remember, the exact timing may vary based on your local climate, so be sure to check with your local extension service or garden center for precise planting dates. Following these guidelines will ensure your onions and leeks are ready to thrive during the cooler months, providing you with a fresh supply of these flavorful vegetables throughout the winter.
Planting your Onions and Leeks
After preparing the soil, it’s time to plant your onions and leeks. For onions, sow seeds in late summer or early fall, or plant onion sets (small, immature onions) in early to mid-fall. Place the seeds or sets in rows, spacing them about 4 to 6 inches apart. Cover them with a fine layer of soil, and water thoroughly.
Leeks can be started from seeds, transplants, or baby leeks (also known as leeklings). If starting from seeds, sow them indoors in late winter for transplanting in the spring. Leeklings or transplants can be planted in the fall. Dig a hole about 6 to 8 inches deep and place the leek in it, then backfill with soil, only enough to cover the roots and a little bit of the base. This will blanch the stem, keeping it white and tender. Space your leeks about 6 inches apart.
Make sure to water your plants regularly, especially during dry spells. A layer of mulch can help maintain the soil moisture and temperature, as well as suppress weed growth. Regularly check your cold frame for ventilation and temperature control. On warmer days, slightly open the lid to prevent overheating and to promote good air circulation, which helps to prevent diseases. With careful maintenance and attention, your onions and leeks should thrive in the cold frame, ready for harvest when the time comes.
Temperature Control in Your Cold Frame
Maintaining the right temperature within your cold frame is vital for the successful growth of your onions and leeks during the chilly months. A cold frame typically warms up during the day through solar energy and retains the heat during the night, creating a warmer microclimate for your plants. However, the temperature can fluctuate due to weather changes, so regular monitoring is necessary.
To monitor your temps, consider investing in a max-min thermometer. This tool will help you monitor the coldest and warmest temperatures in your cold frame each day, allowing you to make necessary adjustments. There are also bluetooth thermometer/hygrometers so you can monitor with your phone. If it gets too warm, simply prop open the lid of your cold frame to let in some fresh, cool air.
On sunny days, the temperature inside the cold frame can rise quickly. To prevent overheating, prop open the lid during the warmest part of the day to allow excess heat to escape. This is especially critical on sunny winter days when the contrast between external and internal temperatures can be significant.
On the other hand, during extremely cold nights, you might need to provide extra insulation. This can be done by draping a blanket or a piece of carpet over the cold frame. Remember to remove it in the morning to allow sunlight in.
Understanding these temperature dynamics and managing them efficiently is the key to thriving onions and leeks in a cold frame during winter. With proper care and attention, you can enjoy a fantastic yield of fresh, homegrown produce.
Harvesting Your Winter Onions and Leeks
The timeline for harvesting onions and leeks can vary based on the specific variety and growing conditions, but a general guideline can be followed.
Onions are typically ready for harvest in about 8-9 months after planting. You’ll know they’re ready when the bulbs are big and the tops have started to yellow and fall over. At this point, gently pull the onions from the ground and let them dry in a well-ventilated, shady spot for a few days.
Leeks, on the other hand, can often be harvested throughout winter and into early spring, depending on the variety. This means you could be harvesting leeks 6-7 months after planting. Harvest leeks when they are at least one inch in diameter. Use a garden fork to gently loosen the soil, and then carefully lift the leeks out of the ground.
In both cases, remember that patience is key. Waiting until your onions and leeks are fully mature before harvesting will ensure you get the most flavorful and nutrient-rich produce from your winter garden.
Happy Gardening!
Growing onions and leeks in a cold frame this winter is a great way to extend your gardening season and enjoy fresh, homegrown produce all year round. With the right cold frame, soil preparation, planting, watering, and feeding, you can grow healthy, tasty plants that are resistant to pests and disease. So why not give it a try and experience the joy of winter gardening today!
Please be sure to check out my Gardening Blog Post page for more growing tips on Cold Frame gardening, Indoor Bulb Gardening, Hydroponic Gardening, Container Gardening, Mums, Herbs, African Violets, planting Bulbs, Flower Gardening, Vegetable and Fruit Gardening, Indoor Houseplants of all kinds, Cactus, Succulents, Hanging plants, Deer resistant plants and even Bird, Bee, Butterfly and Hummingbird Gardens!