How deep should you plant allium bulbs? Horticultural experts share their advice
Looking to plant some allium bulbs this season? Here's how to get it right
While many of our favourite flowers are withering away, now is the time to start thinking about next year's blooms. Alliums are one of the flowers which need planting now, so we asked the experts how to get it right.
With so many bulbs to plant now for a colourful spring display, it's all too easy to rush the planting process and forget what you need to ensure the plants get the best chance of success. So although you may have lots to tick off your September gardening jobs, when planting your allium bulbs, there are a few key details to consider.
One of these is how deep you plant the allium bulbs. Just as tulip bulbs have to be planted at a certain depth, these tall purple flowers also require a little more consideration when planting bulbs.
How deep should you plant allium bulbs?
As one of the best drought-tolerant plants, alliums are a great addition to your garden as summers get hotter and drier each year. To ensure the flowers establish properly, though, you've got to get the bulb planting right.
"For most ornamental alliums, aim for a planting hole around three to four times the bulb’s size, checking the packet for the particular variety," explains Dr Russell Sharp, Founder of Eutrema. Measure from the soil surface to the base of the bulb, rather than putting that much soil above its tip."
"Many border alliums need a hole about 10–15cm deep, while larger bulbs may need 15–20cm. Adequate depth helps protect bulbs from temperature changes and gives developing plants a secure position. Don’t plant every bulb at the same depth regardless of its size," he adds.
If you plant your bulbs right, you won't need to worry about protecting them from frosts when winter arrives.
Dr Russell is an innovator, best known for developing the range of plant care products offered by his company, Eutrema.
Can you plant alliums too deep?
If you're worried about making an autumn garden mistake when planting your bulbs, it's good to know that you can plant your bulbs incorrectly.
"Yes, particularly if you bury small bulbs much further down than their planting instructions suggest. The shoots have further to travel before reaching daylight, which can delay emergence and use more of the bulb’s stored energy," says Dr Russell.
"In heavy soil, a deeper hole may also leave the bulb sitting in wetter conditions, increasing the risk of rot. A few extra centimetres in freely draining soil usually aren’t a disaster, so don’t dig everything up over a small measuring error. Correct bulbs you’ve buried substantially below their recommended depth," he continues.
Alliums are not best suited to wet gardens, so you should avoid putting them in an environment where they could be sat in water.
How many allium bulbs should you plant together?
While you may want to make your cottage garden ideas come to life, you can only plant so many bulbs together.
"I’d start with five or seven bulbs of one variety for a group in a border. That gives a more noticeable display than isolated flowers dotted around the garden, while still allowing each flowerhead to stand out. Treat this as a design choice, rather than a rule the plants need you to follow," recommends Dr Russell.
"Keep smaller alliums roughly 8–10cm apart and allow at least 20cm between taller types, checking the variety’s instructions. Planting together means creating a group across an area, not squeezing several bulbs into one hole," he points out.
What month is best to plant allium bulbs?
Wondering when you should plant these spring bulbs? To ensure you enjoy the blooms come next spring, you can plant the bulbs earlier than you may think.
"Allium bulbs are best planted between early and mid-autumn, or between September and November. They can still be planted in December if you miss this window, but check that the bulbs feel firm and show no signs of mould. Bulbs planted later may flower later than usual in their first year, but should flower at their normal time after this," suggests Richard Barker, horticulture expert and Commercial Director at LBS Horticulture.
With 4 years in the industry, Richard is a gardening expert at LBS Horticulture. He is keen to share his knowledge with both experienced and beginner gardeners, and prides himself on keeping up to date with the latest horticultural trends.
Want to do something a little different with your garden? Why not try some expert tips for planting spring bulbs in your lawn this autumn? It gives your space a whimsical, meadow-like appearance and breaks up a uniform lawn.
