Learn how to plant allium bulbs, including the proper depth, spacing and light levels, so you can enjoy a beautiful display in the spring!
Allium bulbs have a lot to offer you and your garden. While these plants are best known for the familiar edible types like onions, garlic, shallots, and chives, many delightful, spring-blooming ornamental allium species are available to spice up your garden landscape.
The non-edible bulbs of ornamental varieties produce attractive, colorful, and sometimes enormous globes of flowerets that rise above the ground on slender stalks to delight the eye.
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Benefits of Planting Alliums
Besides being beautiful to look at, allium flowers have the additional benefit of attracting garden-friendly insects such as butterflies and bees, and they make excellent cut flowers.
In addition, they are hardy plants that tolerate cold weather and minimal watering as long as you choose the right spot in the garden and plant them at the proper depth and spacing.
Where to Get Allium Bulbs
You can find a wide range of allium bulbs in garden stores, online, and mail-order catalogs. In addition, once you have a patch of alliums growing, you can dig up new bulbs as they multiply from the old plants. It is best to dig up offshoot bulbs in late summer or fall after the plants finish flowering.
If you buy bulbs at a nursery or online, unpack them immediately when you get them home. If you can’t plant them directly, store the bulbs in a cool, dry area until you are ready to put them in the soil.
Where to Plant Allium Bulbs
While allium bulbs are not fussy plants, they do need plenty of sun exposure and well-drained soil to thrive. So choose a spot that gets full sun all day and where the soil quickly drains away excess water.
If the soil is heavy or prone to standing water, find another location, or amend the ground with lots of compost to improve drainage before you plant.
When to Plant Alliums Bulbs
The best time to plant alliums is in the fall when the soil temperature reaches 60°F or less at midday. By planting them in the fall before the first hard frost, you provide the bulbs with the low temperatures and soil moisture they need to develop a healthy root system before they send up shoots and produce flowers in spring and early summer.
In colder areas, the optimum time for planting alliums is in September and October. However, if you live in a warmer climate, you can plant them in October and November.
But fall is a busy time in the garden, and maybe you just realized you didn't get those bulbs into the ground yet. How late can you plant allium bulbs? If you can still dig a hole in the soil, you can plant them!
Once the ground is frozen, you should wait until it thaws before planting. If you don't get your bulbs into the ground in the fall, you can wait until spring. You probably won't get blooms that year, but they'll be ready and waiting next spring. But don't save them until the following fall or they may not bloom at all!
How Deep to Plant Allium Bulbs
The best depth for planting allium bulbs depends on the size of the bulb. A good rule of thumb is to plant bulbs twice as deep as their size. For smaller bulbs, dig down about 4 inches. Plant larger varieties, such as this giant Globemaster Allium, go a bit deeper, between 6 and 8-inches.
Planting at the correct depth is crucial so the growing bulbs won’t get too hot or too cold as the seasons change. Also, when you set the bulbs into the soil, be sure the pointy end is facing upward because this is where the sprout emerges while the roots grow from the rounder end of the bulb.
I like to use a hand shovel to gauge the depth of my hole. The metal part is about 6 inches long, so it's easy to see when I've reached the proper size for my bulb.
How Far Apart to Plant Allium Bulbs
If you are planting allium bulbs in the ground, put them at least 6 to 8 inches apart, or three bulbs per square foot. Keep in mind that some varieties grow quite tall, so consider planting the bulbs behind other perennials rather than right up front.
If you grow them in containers, you can put them closer together. However, when planting in containers, keep some space between the bulbs so they do not touch one another.
Caring for Allium Bulbs after Planting
Once your allium bulbs are in the ground, water them thoroughly to help compact the soil and to initiate root growth. After that, allium bulbs need minimal watering. However, if there is no rain for a week or more, give the bulbs light watering so they do not dry out.
I like to spread a layer of mulch over the bulbs after planting in the fall. It provides the bulbs with additional protection in the cold winter months, and prevents weeds from popping up in the spring. However, don't mound it up too high, or the Alliums will have trouble breaking through to the sunlight.
For the best color, maintain a pH level of 6-7 in your soil. Use a mild fertilizer such as lime, bone meal or bulb booster to supplement your soil if necessary.
Once the plants have flowered, you can dead-head the flowers, but don’t cut down the foliage until it is completely dried. Leaving the foliage on allows the plants to continue photosynthesizing and nourishes the bulbs underground so they will be vigorous when they sprout the following season.
Frequently Asked Questions about Allium Bulbs
Are allium bulbs perennials?
Yes, alliums are perennials, which means that once you plant them, they will sprout and bloom from the same bulb over and over for many seasons.
Do allium bulbs multiply?
Yes, these plants produce smaller new bulbs under the soil as they grow, so they will multiply and spread on their own or provide you with new bulbs to dig up and plant in other locations.
Can you plant allium bulbs in spring?
Yes, you can plant alliums in the spring. However, if you do, the bulbs are not likely to produce flowers until the following spring. For this reason, most people plant alliums in the fall to enjoy the flowers at the start of the next growing season.
Can you plant allium bulbs in containers?
Yes. Alliums can grow in containers. You can plant the bulbs closer together than in the ground, but always leave at least a few inches between the bulbs. You can also combine alliums with daffodil and tulip bulbs for a spectacular container garden display of spring color.
If you plant alliums in a container, keep in mind that above-ground planting does not protect the bulbs from temperature fluctuations as well as the ground does. Therefore, if you live in an area with cold winters, you might want to bring the containers indoors (like a garage, basement or shed) to protect them during the coldest months.
Check out these other bulb planting tutorials!