Allium is a genus of plants that everyone’s seen; many have grown wild in their backyards, yet few truly appreciate the value of these plants.
The word allium literally means garlic in Latin, and while we now tend to eat only about 12 species, far more have been used in yesterday’s kitchens.
Let’s take a moment to look at this genus and some of its wonderful benefits for your garden, regardless of whether you intend to harvest it for food.
Allium Companion Plants
Alliums are incredible companion plants that not only provide some health benefits when eaten (if you use an edible species) but also have health benefits for other nearby plants.
Here’s everything you need to know about using alliums in companion planting.
What is Companion Planting?
Companion planting is the secret to why some gardens are healthier and look much more attractive than others.
Also known as complementary gardening, the goal of this technique is three-fold:
- Group plants that can protect each other from pests or disease.
- Group plants that visually complement each other.
- Group plants with similar needs but different root depths so they can be grouped more closely without competing for resources.
In garden settings, water and nutrients will work their way deeper into the soil, so having a tap root, for example, will be able to claim resources that a plant with shallow roots didn’t get in time.
This little trick means you can plant in the spacing between plants as long as you know the root depths of the plants involved.
Tubers and bulbs are allium’s major root forms, so you will want to mix them with plants with deeper root systems.
Also, many plants attract beneficial insects while repelling pests, and that benefit can carry over to nearby plants as well.
This means less reliance on chemical pesticides, while the closer grouping means less need for herbicides or weeding.
Alliums Aren’t Just Onions and Garlic
Those familiar with the word allium usually only think of those plants used in cooking.
- Chives (Allium schoenoprasum)
- French shallots (Allium oschaninii)
- Garlic (Allium sativum)
- Leeks (Allium ampeloprasum)
- Onions (Allium cepa)
- Ramps (Allium tricoccum)
- Scallions (multiple allium species and variants)
- Wild garlic (Allium ursinum)
But with literally hundreds of species, plus variants and cultivars, there are actually many which serve an almost purely ornamental function.
These often have a single stem with a spherical umbel of bright colors that make perfect accents for the garden, such as:
- Blue globe onion (Allium caeruleum)
- Dutch garlic (Allium hollandicum)
- Giant onion (Allium giganteum)
- Small yellow onion (Allium flavum)
- Star of Persia (Allium cristophii)
Just be warned, a few species in this genus can be considered weeds, so be sure when choosing an allium for your garden that it’s manageable.
Garden Benefits of Alliums
There’s no denying that alliums can be highly beneficial to almost any garden.
Even the purely ornamental plants have a bit of that garlic smell if you bruise the leaves, which helps to repel deer and rabbits.
This smell also helps repel pest insects, such as aphids and mealybugs.
Alliums also help repel slugs, snails, and many more specialized pests when planted near vegetables.
A Note on Grouping Alliums
While alliums are great at deterring a wide range of pests, they’re susceptible to fungal infections and infestation by onion flies.
This can make grouping them together risky, as the collective smell will draw those onion flies in like moths to a flame.
Meanwhile, powdery mildew or other fungal infections can spread like wildfire throughout your allium cluster.
Therefore, it’s best to space your alliums out unless pairing them with plants that repel onion flies.
Leeks are the one exception to this rule, as onion flies seem to dislike them, so pairing a leek with another allium can actually somewhat reduce the risk of onion flies.
Crop Companion Planting
As mentioned, allium can help fight off several crop-specific pests, and some of those crops will also help fend off pests that target alliums in return.
Here are some common crops and their relationship with alliums:
Veggies such as broccoli, cabbage, cauliflower, and kale benefit greatly from having alliums planted nearby.
The alliums will repel cabbage loopers, cabbage maggots, and cabbage worms, among other pests that target these common crops.
Alliums and carrots have an especially close bond, as alliums will repel carrot flies, and carrots will repel onion flies.
Celery helps repel onion flies, helping to keep your alliums safe and healthy.
Planting chamomile near edible alliums will serve as a flavor enhancer for the oils in your alliums.
As a bonus, chamomile will make your alliums less susceptible to fungal infections.
Alliums are susceptible to fungal infections, but the cucumber actually helps protect alliums from this problem.
These wonderful flowers release a chemical that actually kills harmful nematodes and repel onion flies while simultaneously attracting pollinators.
Peppers are a great companion for edible alliums, as the capsicum actually improves the flavor of alliums.
The hotter the pepper, the better your alliums will taste.
Some Other Crop Pairings
Peppers, strawberries, and tomatoes are all less likely to suffer from pests or verticillium wilt when paired with onions.
Planting leeks near other alliums can reduce the risk of onion flies, which the leek is more resistant to.
Lettuce has a compatible root system with alliums, meaning you can plant them very close together.
Parsley deters both onion flies and maggots when planted near alliums.
Crop Plants Harmed by Alliums
Alliums may benefit some plants, but they can stunt the growth of other plants or even degrade their flavor.
Avoid planting an allium too close to the following:
Ornamental Companion Planting
There are quite a few wonderful visual combinations you can make using alliums with ornamentals.
The most common colors of allium blooms are blue, purple, white, and yellow, and their ball shapes add special charm to several types of grass and spike flowers.
Here are just a few of the many wonderful plants that pair great with alliums:
- Asiatic lilies
- Crimson fountaingrass (Pennisetum setaceum)
- Lady’s mantle (Alchemilla mollis)
- Purple coneflower
- White cranesbill
As with crops, ensure that any plants you choose to pair up with alliums don’t compete for root space.