Mature size & growth rate

How big does 'Walla Walla' Onion (Allium cepa 'Walla Walla') get?

Also called Walla Walla sweet onion.

More about 'walla walla' onion

About 'Walla Walla' Onion

Allium cepa 'Walla Walla' · also called Walla Walla sweet onion · edible

'Walla Walla' is a famous short-to-intermediate-day sweet onion with very large, mild, juicy bulbs low in pungency. Traditionally autumn-sown for overwintering and summer harvest, it stores poorly and is best eaten fresh. It needs full sun, rich moist soil, and steady feeding to size up its big, thin-skinned bulbs.

Mature size: Foliage 30-45 cm tall; bulbs very large, commonly 10-15 cm across and up to 0.5-1 kg.

Watch for — Onion fly / thrips: Onion fly maggots tunnel into bulbs while thrips silver the foliage and check growth. Use insect mesh against onion fly and keep plants well-watered to limit thrips damage in hot spells.

Indoor size vs how big it gets in the wild

'Walla Walla' Onion reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back. Indoors and in a pot, expect foliage 30-45 cm tall. In the ground with no restriction it is a completely different plant — bulbs very large, commonly 10-15 cm across and up to 0.5-1 kg. — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Growth rate and years to mature

'Walla Walla' Onion is a fast grower. Realistically, expect a single growing season — it reaches full size in one year, then is done. Its feeding profile backs this up: a hungry crop. feed with nitrogen-rich fertiliser through the leafy growth phase, side-dressing every 3-4 weeks, then stop feeding once bulbing begins so bulbs ripen and skins firm rather than producing soft, late top growth.

Want this turned into the right next pot at the right moment? The pot size calculator and the 'walla walla' onion repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast 'walla walla' onion grows.

How to keep 'walla walla' onion smaller

You are not stuck with the maximum size. For 'walla walla' onion specifically, these are the levers, in order of impact:

Choose a compact or dwarf variety of 'walla walla' onion from the start — that is the most reliable size control for an annual.
Grow it in a smaller container to naturally limit how large it gets.
For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier.
Sow a little later or space plants closer if you specifically want smaller individual plants.

How to grow 'walla walla' onion bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for 'walla walla' onion the accelerators are:

Full sun, warm soil and steady water are what drive a crop to full size fastest.
Sow at the right time for your zone so it gets the whole season to size up.
Feed appropriately for the crop and never let it check (stall) from drought or cold.

Light is almost always the ceiling. The 'walla walla' onion light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When 'walla walla' onion outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for 'walla walla' onion:

It sprawls beyond its bed or container before harvest — usually a spacing or support issue.
It flops or needs staking once it hits full height.
Once it has fruited or bolted, it is at its final size for good — the next plant is a new sowing.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the 'walla walla' onion repotting guide. If you want more of this plant instead of a bigger one, the 'walla walla' onion propagation guide turns prunings into new plants.

'Walla Walla' Onion size — frequently asked questions

How big does 'walla walla' onion get?

'Walla Walla' Onion reaches foliage 30-45 cm tall when grown indoors, and far larger where it grows unrestricted (bulbs very large, commonly 10-15 cm across and up to 0.5-1 kg.). It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Is 'walla walla' onion slow or fast growing?

'Walla Walla' Onion is a fast grower. Expect a single growing season — it reaches full size in one year, then is done. 'Walla Walla' Onion reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back.

How long does 'walla walla' onion take to reach full size?

Roughly a single growing season — it reaches full size in one year, then is done. Light, pot size and feeding move that timeline more than anything else.

How do I keep 'walla walla' onion smaller?

Choose a compact or dwarf variety of 'walla walla' onion from the start — that is the most reliable size control for an annual. Grow it in a smaller container to naturally limit how large it gets. For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier. Sow a little later or space plants closer if you specifically want smaller individual plants.

How can I make 'walla walla' onion grow bigger or faster?

Full sun, warm soil and steady water are what drive a crop to full size fastest. Sow at the right time for your zone so it gets the whole season to size up. Feed appropriately for the crop and never let it check (stall) from drought or cold.