Onion companion plants are better understood as ones that benefit from onions, rather than the other way around. This is because onions have a strong scent, which repels pests from more delicate plants.
Let’s go over some of the best companion plants for onions that are suitable for balcony gardening.
Brassicas are a large family of crops that includes cabbage, mustard, cauliflower, broccoli, and more. Because we eat the leaves (or some variation) and they take a while to mature, they’re ideal companion plants for onions.
Onions repel pests that would otherwise munch on the leaves. You don’t need to keep them in the same soil – nearby will work fine.
Carrots make good onion companion plants for the same reason. The smell of onions deters the carrot fly by masking the carrot’s smell. You can interplant them in large containers (like this), but separate pots also work.
Lettuce grows well alongside onions and fits in nicely with its growth cycle. You can plant lettuce while the onions are still bulbs and harvest it before they need the soil space. Also, lettuce has shallow roots, so won’t compete for nutrients or room.
Onions help repel aphids, slugs, and other pests that might feast on your leafy greens. This also works for spinach and chard.
Mint works the opposite way as a companion plant for onions, but for the same reason. Its strong aroma repels the onion fly, which eats onions. You’ll want to keep mint in its own pot because it’ll quickly steal soil space otherwise.
Marigolds help attract pollinators to gardens but also prevent nematodes from settling in the soil. It’s only the second thing we’re interested in when planting alongside onions.
For this, you’ll want them in the same soil. Planting marigolds in the top of an onion planter (like this) is ideal. Plus, marigolds will help out all your other flowering plants.
Not all plants enjoy the strong aroma of onions. Some things to avoid planting with them include:
It’s believed that onions will inhibit the growth of beans and peas. Unfortunately, this means you’ll have to sacrifice one or the other on your balcony garden. You can grow both as long as you have enough space.
Considering sage is a classic accompaniment to onions in cooking, they don’t get on in the garden. Sage can inhibit the growth of onions. However, you should be fine if you grow them on opposite ends of the balcony, as it’s not a particularly bad issue.
This is by no means a full list of companion plants for onions. There are very few crops that don’t get along with them, and these issues can usually be solved by simply keeping them in different soil. So, if you think your balcony garden will benefit from onions, you shouldn’t have any issues planting them.