Onions and garlic look different in the ground, yet they share deep botanical roots. So, are onions and garlic in the same family? The short answer is yes, and it comes down to one plant genus I grow on my fields every season.

Yes. Onions and garlic sit in the same family, Amaryllidaceae, and the same genus, Allium. Onion is Allium cepa and garlic is Allium sativum. Older books list them under the lily family, but that classification changed.

So, Are Onions and Garlic in the Same Family?

Yes, onions and garlic are in the same family. Both belong to Amaryllidaceae and share the genus Allium. Onion carries the name Allium cepa. Garlic goes by Allium sativum. Botanists group plants by flower structure, chemistry, and DNA, and these two match on all three. That sharp, sulfur heavy smell you get from a cut bulb is a shared family trait. Both crops store energy in underground bulbs. Both send up narrow leaves. Both bloom in rounded clusters called umbels. So they sit about as close as two crops can get without being the same plant.

Why Do Some Sources Say They’re in the Lily Family?

Some sources call onions and garlic lily relatives because that was the accepted classification for many years. Older field guides and seed catalogs placed Allium in Liliaceae, the lily family. Then molecular studies reshaped the family tree. For a stretch, botanists used a separate family called Alliaceae. The current system, set by the Angiosperm Phylogeny Group, folds Alliaceae into Amaryllidaceae as the subfamily Allioideae. So if an old gardening book calls your onions a lily cousin, it was correct for its time. The science simply got sharper. Today, Amaryllidaceae is the family that holds up.

What Other Crops Share the Allium Family?

Several kitchen staples share the Allium genus with onions and garlic. Leeks, shallots, chives, and scallions all belong here too. Shallots and scallions are close cousins of the common onion. Chives are the smallest of the group, grown mainly for their leaves. Leeks trade a tight bulb for a thick white stalk. Ornamental flowering alliums round out the genus in the flower bed. Every one carries that same allium bite. When I map out my beds each year, I treat this whole group as one family for rotation. That matters more than most gardeners expect.

How Are Onions and Garlic Different Within the Same Family?

The biggest difference is bulb structure. An onion forms one layered bulb, while garlic splits into a head of separate cloves. Slice an onion and you get concentric rings. Break a garlic head and you find eight to twenty cloves, and each clove can grow a new plant. Onions usually start from seed, sets, or transplants, and growing onions from seed gives you the widest choice of varieties. Garlic almost always grows from a planted clove. Onions also respond strongly to day length, which sets their bulbing time. Garlic leans more on a cold winter spell. Same family, yet each one earns its keep in its own way.

Does Sharing a Family Change How I Grow Them?

Yes, sharing a family means onions and garlic attract the same pests and diseases. So I never rotate one right after the other. White rot, onion maggots, and thrips hit the whole Allium group. If garlic grew in a bed last season, planting onions there next feeds those same soil problems. Because of that, I keep at least three years between any allium crop in one spot. Building that gap into your crop rotation is the best move you can make for allium health. It also helps to plan when both go in the ground. Garlic and onions often share a fall or early spring planting window.

Can You Plant Onions and Garlic Near Other Crops?

Yes, both onions and garlic work well as companion plants because their strong scent keeps many pests away. That same allium chemistry that guards the bulb also guards its neighbors. Gardeners often tuck them beside carrots, lettuce, and tomatoes. For the details, I have covered setting onions beside carrots and pairing garlic with potatoes in their own beds. Just keep alliums away from beans and peas, since those two tend to struggle next to them.

Final Thoughts

Onions and garlic are close kin, both Allium members under Amaryllidaceae. In the kitchen, that shared family explains their matching bite. In the soil, it explains why they should never follow each other in rotation. Treat the whole allium group as one team. Do that, and you will grow healthier onions and garlic season after season.