Most of how to grow alliums well comes down to three things going right. They need to go in deep enough that they stand up, they need something growing around their feet to hide what the leaves are doing by the time the flower opens, and they need leaving alone until the middle of July. Everything below is those three things.
WHEN TO PLANT ALLIUM BULBS
Early autumn is the moment. The ground is still warm enough for roots to move and cool enough to hold back trouble, and alliums want that root system in place well before winter because they carry their whole first season inside the bulb already. September into October is the window.
There is one decision that costs people money every year. Alliums appear everywhere in spring as pots of green shoots at several times what the same variety costs as a dry bulb in September, and you get one plant where you could have had a group. Buy them in autumn and plant them in threes and fives.
HOW DEEP TO PLANT, AND WHY ALLIUMS FLOP
The flower stems emerge from the side of the bulb rather than the centre, and if planting is too shallow, they can tend to flop in exposed positions. That single fact is the answer to most allium disappointment, so put 10 to 15cm of soil over the bulb (4 to 6 inches) and err on the deeper side, because depth does the job people try to do later with a cane. Deep is the staking.
Spacing depends on what you have bought. The smaller kinds sit happily at 8 to 10cm apart and want to be in a group to register at all, while the big drumstick sorts need 20cm or more, both because the heads are wide and because crowding them is how you get thin stems. Give the big ones room.
DO ALLIUMS NEED STAKING
Almost never, if they went in properly. A tall allium in an open windy border is the exception, and there a stake put in at planting rather than pushed through the clump later will do it, but the honest answer for most gardens is that a leaning allium is telling you it was planted too shallow. Fix that in autumn, not in June.
WHAT TO GROW ALONGSIDE ALLIUMS
Anything leafy that will cover their feet, and shorter alliums to circle the tall ones. Taller types circled with complementary smaller varieties can be particularly effective, and a few tall alliums planted through a drift of shorter ones is better still, because the eye reads the repetition before it reads any single flower. Plant more than you think.
The other job is cover. Try planting these in mixed borders and amongst shrubs that only cast light shade in May and June, and put something leafy at their feet, because the allium will be a bare stem by the time it flowers and it wants a neighbour standing in front of its ankles. Geraniums do it, so do nepeta and alchemilla.
The largest head of all, and the one to put at the back.
Blue spires at the same moment, and the shape alliums do not have.
Low, yellow and early. Good circling the taller sorts.
WILL ALLIUMS FLOWER THE FIRST YEAR
A top size bulb flowers the spring after you plant it. That is worth saying because alliums are one of the few things where the small cheap bulb is a genuinely false economy, since it will give you a smaller head in year one and may take two or three seasons to reach the size shown on the packet. Buy the biggest you can.
After that first year they get better rather than worse. The bulb builds while the leaves are up, so the head you see in the second and third June is usually larger than the first, and a clump left undisturbed reaches its best somewhere around year four. Patience is cheaper than replacement.
CAN YOU GROW ALLIUMS IN POTS
Yes, and the big ones are better in a pot than people expect. When planting in the border and especially important for container planting, it is essential that they are planted deep enough, so use a deep pot rather than a wide shallow one and get 15cm of compost over the bulb. A shallow pot is where alliums lean.
Two things then decide whether it works. The compost has to drain, because an allium sitting wet through winter is the one way to lose one, and the pot wants standing where you will see it in June and can move it out of the way in July when the leaves go over. Crocks in the bottom, and no saucer.
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ARE ALLIUMS GOOD FOR BEES
Yes, and among the best you can plant for them. The globe is not one flower but dozens of small ones opening over a fortnight or more, so a single head goes on feeding long after a tulip has finished, and on a warm afternoon you will hear a big allium before you reach it. Plant them where you walk past.
The drumstick allium, latest to flower and never without bees on it.
A wide open head of stars that holds its shape for weeks.
White with a green eye, and quietly one of the best.
WHERE TO GROW ALLIUMS SO THEY NATURALISE
There is an argument for putting them somewhere you do not tend. Alliums are not as widely grown as they should be, and they are one of the most useful plants for naturalising in a shrubbery or woodland, where nobody is weeding, nothing gets lifted, and a group thickens quietly over five or six years into a drift you could not have planted on purpose. Rough ground, then.
WHEN TO CUT ALLIUMS BACK
Mid July, and later than most people think. The heads are worth leaving as long as they hold their shape, and there is no need to take them off at all if you like them standing through August, but the moment they start to collapse and drop seed everywhere is the moment to cut. Ours come off as the agapanthus take over.
Cut a few for the house while you are at it. The stems still look attractive at this stage, and if you want them to dry properly then take them before the seed loosens, stand them somewhere airy and out of direct sun, and they will hold their shape until Christmas and beyond. Dried too late and they shatter.
WHAT CAN GO WRONG WHEN YOU GROW ALLIUMS
Very little, which is part of the appeal. The foliage can have an unpleasant onion smell when broken, just be careful not to trample on them, and the only real disappointment is a thin weak stem, which comes from crowding or from competition at the base rather than from anything wrong with the bulb. Weeds are usually the culprit.
Two things are worth knowing rather than worrying about. Slugs will take the young shoots in a wet spring, and alliums should not go where onions or leeks have been grown recently, because the soil borne troubles that affect the vegetable affect the ornamental in exactly the same way. Neither is common in an ordinary border.
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