When to Harvest Your Onion Sets
Harvesting onion sets, typically undertaken in late summer, is a distinct process from gathering mature onions grown from sets. The primary goal when harvesting sets is to dig them up at the right time so they can be dried and stored for planting the following spring. Unlike mature onions, which are harvested when their foliage yellows and dies back, onion sets are usually lifted when the parent plants have reached a specific size and maturity, often indicated by the tops starting to wither but still being somewhat green. This timing is critical to ensure the bulbs have developed sufficiently to store well but haven't become too mature or started to bolt (send up a flower stalk), which would render them unsuitable for storage as sets.
- Harvest sets when tops begin to wither but remain partially green.
- Timing ensures good storage quality and prevents bolting.
- Dry conditions are ideal for lifting bulbs.
- Handle bulbs gently to avoid damage.
Determining the precise moment for lifting your onion sets involves observing the growth habits of the specific varieties you've planted. Generally, this occurs around August or September in many temperate climates. The foliage might be starting to flop over or yellow at the tips, but the majority of the leaves should still appear reasonably healthy. If the tops have completely died back, the bulbs may have already matured too much for ideal set storage. Conversely, lifting them too early means they might not have developed enough to store effectively, potentially leading to rot or premature sprouting in storage. Aim for a period when the soil is relatively dry, as this makes the harvesting process much cleaner and easier, reducing the risk of soil-borne diseases adhering to the bulbs.
Assessing Bulb Maturity
To gauge maturity, gently pull a few plants from the ground. Look for bulbs that have reached the desired size – typically between a large marble and a small golf ball. If the roots are still robust and the green tops are vigorous, they may need a little more time. However, if the leaves are showing signs of natural senescence (aging), it's a strong indicator that the plant is redirecting its energy downwards, preparing the bulb for dormancy. This is the sweet spot for harvesting for storage.
Ideal Weather Conditions
The weather plays a significant role. Harvesting on a dry, sunny day is highly recommended. This allows the bulbs to begin drying immediately after lifting, which is crucial for preventing fungal infections and rot during storage. If you harvest in wet or damp conditions, you'll need to be more diligent about drying them thoroughly indoors before storing, which can be a more challenging process.
Gentle Extraction
Use a garden fork or trowel to loosen the soil around the onion sets, being careful not to pierce or damage the bulbs. Gently lift them from the ground, keeping the foliage intact as much as possible. This leafy material will be useful for handling and drying the sets.
The Harvesting and Drying Process
Once your onion sets have been carefully lifted, the next critical phase is their preparation for storage, which centres on meticulous drying. This isn't just about removing surface moisture; it's about ensuring the bulbs are completely dehydrated to prevent rot, disease, and premature sprouting. The process requires patience and the right conditions to achieve success. Proper drying is paramount; failure here often leads to disappointment when it comes time to plant them out in the spring.
Initial Curing
After gently shaking off excess soil (avoid washing them, as this can introduce moisture and pathogens), spread the onion sets out in a single layer on trays, old newspaper, or mesh racks. Ensure there's good air circulation around them. The ideal location is a warm, dry, well-ventilated area, such as a greenhouse, a dry shed, or a covered porch. Direct sunlight can sometimes scorch the bulbs, so a bright, airy spot away from intense sun is usually best. Allow them to cure for at least one to two weeks. During this period, the roots will wither completely, and the outer skins will become papery and dry. The foliage should also dry out and become brittle.
Checking for Dryness
You'll know the sets are sufficiently dry when the roots are brittle and snap easily, and the necks of the bulbs are completely sealed and dry, with no signs of softness or moisture. The papery outer skins should be completely dry and rustle when handled. If there's any hint of dampness or softness, especially around the neck, they require more drying time. This stage is non-negotiable for successful long-term storage.
Trimming for Storage
Once thoroughly dried, you can trim off the dried foliage and roots. Leave about an inch of the stem attached to the bulb. This trimming helps to prevent the spread of any lingering fungal spores and makes them neater for storage. Be careful not to cut into the bulb itself, as any damage can create an entry point for rot. This step makes them more manageable and less prone to damage in their storage containers.
This methodical approach ensures that the onion sets are in optimal condition, ready to lie dormant until planting time, a testament to good horticultural practice.
The entire success of storing onion sets for future planting hinges on one factor: they must be bone dry before they go into storage.
If you're drying them on mesh racks, gently turn the sets every few days to ensure even drying on all sides.
The proper drying of onion sets is a non-negotiable step for successful storage.
Storing Your Harvested Onion Sets
Storing onion sets correctly is as vital as harvesting and drying them properly. The aim is to keep them in a dormant state, preventing them from sprouting prematurely or succumbing to rot, ensuring they are viable for planting when the time comes. This requires a specific environment that mimics their natural dormancy period, cool, dark, and dry. The containers you choose and the storage location are key factors in maintaining their quality over the winter months.
Choosing the Right Storage Container
Avoid airtight containers, as these trap moisture and will lead to rot. Breathable materials are essential. Traditional methods include using old net bags (like those onions are often sold in), hessian sacks, or shallow wooden crates lined with newspaper. You can also use shallow cardboard boxes, ensuring they aren't overfilled, so air can circulate. The key is to allow air to flow freely around the sets, preventing condensation and humidity build-up. If using boxes, a single layer is preferable; if layering is unavoidable, place a layer of dry newspaper or straw between batches.
Ideal Storage Conditions
The optimal storage environment for onion sets is cool, dark, and dry. A temperature range of 4-15°C (around 40-60°F) is generally ideal. Avoid freezing temperatures, as these can damage the bulbs, but also avoid overly warm conditions, which encourage sprouting. A frost-free shed, an unheated garage, a cellar, or a cool pantry are often suitable locations. Crucially, the area must be dry; high humidity will encourage mould and rot. Ensure the storage area is also protected from pests like mice or rats, which can damage the sets.
Regular Inspection
It's advisable to check on your stored onion sets periodically, perhaps once a month, throughout the storage period. Look for any signs of mould, rot, or premature sprouting. Remove any affected bulbs immediately to prevent the problem from spreading to the rest of the batch. Healthy sets should feel firm and dry. If you notice any softening or dampness, they may need to be taken out and re-dried for a short period, provided the conditions are suitable.
Considering Alternatives for Storage
While the net bag or crate method is standard, some gardeners experiment with other breathable solutions. Some use shallow seed trays stacked with adequate spacing, while others employ old fruit nets. The principle remains the same: ample airflow and a dry, cool environment. Regardless of the specific container, the goal is to provide a stable, dormant state until the planting season arrives. It's worth noting that sometimes, even with the best care, a small percentage of sets may not store perfectly, but this is a natural part of the process.
To prevent cross-contamination if you're storing different varieties, label each bag or container clearly.
The right storage environment is crucial for maintaining the viability of your onion sets.
Preparing Onion Sets for Planting
As spring approaches, the anticipation of planting your stored onion sets builds. Before they go into the ground, a final check and preparation are necessary to give them the best start. This involves assessing their condition after storage and ensuring they are ready to grow. While many sets will be in excellent condition, some might show minor signs of their long dormancy, and addressing these ensures they perform optimally when planted out.
Final Condition Check
When you are ready to plant, take your stored sets out and inspect them. They should feel firm and dry, with brittle, withered roots and dry, papery skins. Some slight shrivelling is normal, but any bulb that is soft, mouldy, or has significant rot should be discarded. You might see a tiny bit of green shoot already starting, which is usually fine and indicates they are eager to grow. If the roots are still somewhat pliable, this is also not a problem.
Soaking (Optional)
Some gardeners choose to soak their onion sets for a few hours (no more than 12) in lukewarm water before planting. This can help to rehydrate them slightly, especially if they appear a bit dry or shrivelled, and can encourage faster root development once planted. You can add a mild plant starter solution or a tiny amount of seaweed extract to the water if desired, though plain water is usually sufficient. This step is not essential but can be beneficial, particularly if your sets have been in storage for a long time or the conditions were very dry.
Planting Out
Once prepared, it's time to plant. Onion sets are typically planted pointy-end up, about 2.5-5 cm (1-2 inches) deep into well-prepared soil. The spacing between sets depends on whether you want to grow them into large onions or smaller spring onions. For larger onions, space them about 15 cm (6 inches) apart, and for spring onions, you can plant them closer, around 5-7.5 cm (2-3 inches) apart. Ensure the soil is moist but not waterlogged. Planting them out when the risk of hard frost has passed is advisable, typically from late March to April in the UK, depending on your local climate and soil temperature.
What to Do with Unsuitable Sets
If you find sets that have rotted or are clearly not viable, do not plant them. They will only spread disease. However, if a set is merely shrivelled or has a tiny sprout, it can often still be planted, especially if you're planting them out immediately. The risk of bolting is higher for sets that have started to sprout significantly before planting, but they can still produce edible onions. The key is to assess each bulb individually and plant out only those that show signs of potential growth without obvious decay.
The careful preparation of onion sets before planting is the final step in ensuring a successful harvest.