There are a few questions in the gardening world – ‘When are onions ready for harvest?’ included – that no one ever truly knows the answer to. I can tell you what to look for, and about the signs your onions are ready to harvest. But with so many different ways to plant onions and so many different types of onions, it’s impossible to give a single answer, and it certainly isn’t as straightforward as ‘onions are ready for harvest in September’!
So, when are onions ready for harvest? First, let’s learn the signs, then we’ll try to break down the main groups of onions, and the main growing methods, so you can at least roughly know when to start checking onions for harvest.
Signs that onions are ready to harvest
Onions that are ready for harvest have flopped leaves. In good weather, this should be the first sign that your onions are ready to harvest. Obviously, following particularly high winds, or if you’ve tried onion leaf folding for bigger bulbs, then this won’t work for you, but it’s a solid indicator that the bulbs have stopped sending water to the leaves, and the cell structure above ground has stopped forming rigid growth.
Once the leaves have turned a papery yellow (this usually starts from the tips) they are almost definitely ready for harvest. Eventually, the leaves will flop to the ground and lay there. There is no time to waste when this happens, and you need to go out rain or shine before your onions start to enter their energy conservation stage and lose their bite.
When is it too late to harvest onions?
If the leaves have fully died back, it is likely that your onions will have rotted underground, or at the very least started to soften and form next year’s bulbs.
We did this last year by accident, as part of our garden is dedicated to cottage garden growing, with vegetables mixed in with ornamental planting. We forgot about a block of onions, and they flowered really beautifully the following year, with really tight allium flower heads, that lasted all summer.
So, if you do forget about your onions, it’s not the end of the world and they can be a wonderful surprise flower in the garden next year even if you don’t get to eat them.
Can you eat bolted onions?
If your onion has bolted and grown scapes at the top of a stem, it can still be harvested. However, it will have a harsher texture, contain more water, and cook slower than a normal onion. Its flavor can also be a bit of shock to the system, so it’s best to add it to soups in small quantities.
Bolted onions shouldn’t be eaten raw in salads as they can cause mildly upset tummies.
What months are onions ready for harvest?
For most temperate climates, it can be anything from July to September, depending on your weather, sowing and planting dates.
The best way to determine when an onion is ready for harvest, is by the signs listed above, rather than by date, as all onions will crop at different rates, but to help provide some sort of guide to the date ranges you should be looking at for harvesting your bulbing onion crop, we’ve split onions into a few major groups below, which hopefully demystify the process a little.
When are fall onions ready to harvest?
Fall onions planted out directly into the soil in September or October can be harvested as early as June.
Sets that have overwintered in modules are usually ready for harvest in August or early September.
Both ways produce earlier onion harvests than onions from seeds, seedlings, or sets planted in spring, but there is a significant difference in the speed of cropping between plants overwintered in the soil compared to plants overwintered in modules.
When are onions from seedlings ready to harvest?
Onions planted from seedlings, bought and planted in spring, will be ready to harvest in late September, or early October (early autumn). They are slower to start forming bulbs, and there can be big discrepancies in northern climates compared to southern climates, so again, pay attention to the visual signs as your final guidance.
When are spring-planted onions ready for harvest?
Onions planted from seed in spring are the slowest to crop and are usually ready to harvest in October, or even November in milder climates. They will inevitably have smaller bulbs than onions planted in fall, or from sets, but the signs they’re ready to harvest will be the same.
Look for drooping leaves in particular as the shorter plants find it easier to feed the leaves and are less likely to develop papery leaves at the same rate as fall onions. When the leaves begin to droop they are usually ready to harvest.
How to harvest onions
The trick to harvesting onions is patience and a light touch. If you damage the base plate or leaves of the onion by pulling too harshly, it will be almost impossible to store them properly.
Gently loosen the soil around the base of each plant with a hand fork or a trowel, while firmly holding the base of the onion and gently pulling straight up out of the soil. If the onion seems stuck in place, keep teasing it out with a trowel until it slides out of the soil, making sure not to damage the leaves or root plate in the process.
If you accidentally damage the onion, it can be eaten straight away but won’t store for more than a few days before the cut starts to turn bad.
Best conditions to harvest onions
For the easiest onion harvesting experience, wait until just after heavy rainfall. The water will loosen the soil around the base of the plant, making it much easier to pull the entire plant out of the soil without causing any damage.
By the time you come to harvest, it is too late to plan soil conditions, but a loose, free-draining soil is ideal and gives their bulbs space to grow, with minimum resistance when you come to harvest onions. While onions will grow in clay soil, they prefer looser soils as they tend to restrict their growth less, and are less likely to cause waterlogging and root problems.
You can replicate the wet conditions for harvesting by watering the soil half an hour before harvesting onions, which will help loosen the soil up just enough to tease the bulbs out, roots and all.
How to cure onions
To dry onions for storage, they must be left in a warm dry place for 2-3 weeks. The ideal spot is on a shelf or staging in the greenhouse, where they will really bake. If you don’t have a greenhouse, then you can lay them out on a patio in sunny weather, or cover them with a sheet of glass or a clear plastic tent as long as they are raised off the ground to stop them drawing moisture up.
Wherever you cure onions, make sure they are not touching each other as airflow is important to prevent rot.
As long as they are kept dry and warm for three weeks, without any risk of moisture, they will begin to develop the papery skins you’re familiar with from supermarket onions.
The most important part, though, is that they must have their root pates and leaves attached for this entire period. Leaving the leaves and roots in place allows the plant to callus, without forming any rot on the bulb itself. This provides a barrier against bacteria that can enter into the moist bulbs before their outer skins dry out.
A particular note about the leaves stems from the way onion bulbs grow in the first place – the leaves are the top of the bulb. Every leaf on an onion forms the top of one layer of the onion bulb. Cutting a leaf off can speed up the decomposition of that layer of the bulb. By keeping them attached until they dry completely, the bulb has the best chance of creating its own natural callus.
When the leaves have dried completely, cut them back to around 1-inch above the tip of the bulb. This allows any slow drying central leaves to continue drying and lets you prepare your onions for storage.
How to store onions
When harvesting onions, there are two choices. One, eat them all at once and risk losing all your friends as a result of your newly acquired breath. Two, store them and benefit from your harvest for the next few months.
To store your onions, keep them in a cold dark place, away from direct sunlight. A pantry or kitchen cupboard is usually fine but for a huge harvest, a dry potting shed, or garage is perfect. Just like storing apples, onions will last longer if you can keep them from touching each other (this stops one bad onion from ruining a whole bunch).
Onions are really space-efficient vegetables to grow in the garden, but their tendency to bolt and desire to flower means you need to pay attention to them. After a good season of growth, you can have homegrown onions ready to eat right through winter if you plan well enough.
Onions will tell you when they are ready for harvest, so the question isn’t ‘When are onions ready for harvest?’ but ‘What are the signs that onions are ready for harvest?’