You harvest bulb onions when the leaves flop over and are lying on the ground. If you have a VERY hard freeze (10F or so), leaves may simply die, in which case you just cross your fingers and hope that the bulb will resprout. That happened to me a month ago.

Those appear to be very young plants and in bunches of 3-4?, maybe good for using as "spring" onions now? But if my eyes aren't fooling me these "bunches" won't produce large bulbs since they are crowded together.

They're actually 3 bulbs that we got from the supermarket and they sprouted. I planted them about 6 inches apart. Should they have been planted further apart then that? The leek in the middle is a volunteer. I'll watch for the leaves falling over.

Standard spacing for bulb onions is 4", so you're good to go. Note that onions don't even begin to produce real bulbs until a month or so before harvest. At that time, the leaves should be 2-3 feet long. Hard to tell from your pictures, but your plants don't look that mature. Not quite sure what to expect if you're repurposing onion bulbs from the supermarket.

If they are supermarket bulbs that sprouted, you aren't likely to get bulb onions from those. Supermarket bulb onions are already done with their first year growing and are dormant. When they sprout, the are going into their second year of growing, which is their seed growing year. So energy production will go more into the greens and seed head formation than producing another big bulb.

Some varieties of onions can divide and grow that way, but the varieties commercially grown for supermarkets tend not to do so since a single bulb is more desireable than dividing bulbs for the buyer.

Sprouted bulbs are great for growing onion greens- I regularly have a pot or two in the kitchen window during the winter for them.

I believe pearl onions are just baby onions, and if you plant them from the supermarket, they should grow bulbs. But yes, if you take a large bulb onion, and try to plant a part of it, you'll just get flowers and seeds.

I seem to get grocery store onions sprouting every year. I always stick them in the ground and eventually get a bulb about the size of a golf ball. I've never let them get bigger before using as fresh onions and use the greens too. I've never had them get the thicker stalk that makes a seed head.

Concur: replanted onion bulbs will make excellent green onions in late winter, early spring. They will send up seed heads in spring and you can save seeds. I grow short day Vidalia types. pull them in May. by December they start spouting. so I stick the in the ground and have green onions January and February. until neww crop is big enough to harvest green onion in March and April. Mature onions in May.

Those clusters look like what I get in the 2nd year, when I plant saved bulbs for seed. Those bulbs usually split into a cluster, typically 3-6 plants. If let go, they will send up seed stalks in the Spring (or whatever passes for Spring in your obviously warmer location lol) and eventually form a cluster of small, shallot-like bulbs. I never tried to re-plant those bulblets (DW just made soup from them) but suspect they would act like onion sets.

" I believe pearl onions are just baby onions, and if you plant them from the supermarket, they should grow bulbs."

True, if they were from the supermarket. But just an FYI, calling those small supermarket onions "pearl onions" is a misnomer, much like sweet potatoes being misnamed 'yams', or small pickled cucumbers being misnamed 'gherkins'. The real pearl onion, Allium sphaerocephalum, is an onion relative that looks like a miniature Elephant garlic... and forms clusters of genuinely pearl-sized bulblets under the main bulb. That main bulb seldom exceeds !" wide, but they can be planted densely.

I have never heard Allium spaerocephalum referred to as ’Pearl Onion’. It has many vernacular names, mostly referring to the flower head, for which it is usually grown, but not ime Pearl Onion. Pearl Onion usully denotes Allium ampeloprasum var. sectivum.

I also would not say that calling small pickling cucumbers Gherkins is a misnomer. It's a culinary and usage term, not a botanical definition, denoting certain small cucumber cultivars grown specifically for pickling. There’s nothing wrong with that. It is a useful term imo.