How and when to plant gladioli bulbs: simple tips for beautiful blooms

Our advice on how and when to plant gladioli bulbs will help you grow these structural flowers in your garden

when to plant gladioli bulbs
(Image credit: iBulb)

Our tips on how and when to plant gladioli bulbs are just what you need if you want to grow these gorgeous blooms. They make a beautiful addition to summer flowerbeds or borders, and it's super simple to do once you know how.

Most people consider autumn to be the time for planting bulbs, and in many cases this is true. However, whilst tulips, daffodils, crocuses, and all those other spring flowers need to be planted pre-winter, for gladioli, you need to hang on a few months longer.

It's worth the wait. Although once deemed a little old fashioned, gladioli are making a comeback. With their architectural structure and riot of color, we're not surprised one bit. They look fantastic along the back of a border and, with their long vase life, make an ideal cutting flower. And you can plant them in containers, too.

When to plant gladioli bulbs

First things first – you'll need to know when to plant gladioli bulbs. Well, like crocosmia and bearded iris, gladioli are summer-flowering and therefore need to be planted when the weather is warmer. 

To get ahead, you can start them off in pots indoors in March. Place them somewhere bright and frost-free, like a windowsill or greenhouse.

If you're planting the bulbs directly into the ground or in containers outdoors (or are moving your pre-planted indoor pots outdoors), do so between May and July. 

They will generally begin to flower three months from planting. It's a good idea to stagger your planting with fortnightly intervals – this will reward you with a longer-lasting display of flowers.

purple gladioli

The 'Purple Mate' gladiolus

(Image credit: iBulb)

How to plant gladioli bulbs in a pot

With their vibrant color and eye-catching form, gladioli make lovely additions to container gardening displays. It's simple to do:

  1. In his useful video for the RHS, Robert Evans of Pheasant Acre Plants advises to clean up your gladioli bulbs, otherwise known as corms, before planting them in a pot. Do this by carefully taking off the dry, outer layers of skin with a sharp knife. This will leave the new shoot exposed. Remember to always wear gloves when handling gladioli bulbs – they are toxic to humans and can cause skin irritation.
  2. Next, grab your pot. Bear in mind that some gladioli grow very tall (up to around 4ft). If this is the case with your chosen variety, opt for a larger container.
  3. What gladioli really need is good drainage, says Monty Don on Gardeners' World. 'Add a bit of grit to the compost – you can't really overdo this so don't be coy about it,' he says. Put a layer of this gritty compost in the bottom of the pot.
  4. Add your bulbs, shoot facing upwards. Your bulbs should be spaced around 4–5in apart. But, it does depend somewhat on the variety, so double check your packet for advice. Depth-wise, Monty says, 'As a rule of thumb, you're better to go too deep than too shallow, but you can't go wrong if you do it twice the depth of the bulb.'
  5. Robert Evans advises to never press the bulbs in. Instead, lie them flat on the surface. If you press them, the ring of roots will push up against the compost and the corm will lift, creating a gap between the corm and the compost, he explains. This can dry out the root and lead to the plant wilting.
  6. Once your bulbs are in, cover them with compost, water, and place them somewhere sheltered and sunny.
  7. Even though these plants love the sun, it's important to not let them dry out. As Robert says, when they start to come into flower (when the flower sheath comes through the bud), water two or three times a week.

For extra flexibility, Monty Don says how you can plant your gladioli bulbs in lattice pots (the same you'd use for aquatic plants). You can then sink them into your border, or into a terracotta pot (which are good for drainage), when you're ready to show them off.

gladioli and crocosmia in container

These yellow 'Lemon Drop' gladioli look stunning alongside a red variety, crocosmia and fennel

(Image credit: iBulb)

How to plant gladioli bulbs in the ground

The process of planting your gladioli directly into your borders and flowerbeds is similar to planting them in pots.

  1. Dig a trench or use a bulb planter to make holes in the ground at around 6in deep. As mentioned above, the optimum spacing of your gladioli will depend on the variety of your bulb. However around 6in apart should be about right.
  2. If your garden soil is heavy, add a handful of grit to the hole before carefully placing in the bulb, shoot facing upwards.
  3. If you have chosen a very tall variety of gladioli, you will need to add a stake to support it. It's best to put the cane in place now rather than when the plant has grown, to avoid damaging the bulb.
  4. Cover with soil and top-dress with compost. You can learn all about composting in our guide.
  5. As with growing gladioli in pots, make sure the plants don't dry out. Once they begin to flower, water them two to three times a week.

You can find more flowerbed ideas in our guide.

planting gladioli bulbs

Plant your gladioli bulbs in free-draining soil in a sunny spot

(Image credit: iBulb)

Where should you plant gladioli bulbs?

Gladioli originate from hot climates, so they perform best when planted in full sun. They like well-drained soil, but ensure it's kept moist.

Due to their height, gladioli work well at the back of a border. However, they can also make a striking choice for containers, if you're looking for patio gardening ideas

They are a classic pick for cottage garden schemes, but work equally well in contemporary plots. Try mixing with dahlias and zinnias for a summertime show – our guide on how to grow dahlias is full of useful tips.

gladioli in garden

Plant gladioli along a path for an enchanting look

(Image credit: iBulb)

Do you need to dig up gladioli corms over winter?

Gladioli are perennials, meaning they will flower year after year.

Some gardeners choose to dig up their gladioli corms over winter, similarly to dahlias. But in slightly warmer climates, such as the south of the UK, this isn't strictly necessary as long as you apply a good, deep layer of mulch. The mulch will help to protect the bulbs from frost. You can find out all about mulching in our guide. If you are leaving the bulbs in the soil all year round, it's a good idea to lift them every couple of years and divide the clumps as cormlets will form over time.

For colder regions (USDA Hardiness Zone 7 or colder) or for containers, cut the stems down to around 4in and lift the corms carefully after the first fall frost. Be sure to do this before the first hard frost. 

Once dug up, brush off any loose soil, then lay the corms out somewhere ventilated, frost-free, and dry in trays for winter.

Cormlets (miniature corms that grow on the sides of the main corm) can be removed. Store these and pot them up in spring, but bear in mind that they'll need to be grown for a couple of years until they are large enough to flower.

You can find more advice on what to do with gladioli bulbs when finished flowering in our guide, whilst our feature on how to protect bulbs from frost has more useful tips.

gladioli bulbs

Gladioli bulbs can be dug up and stored over winter to protect them from frost

(Image credit: iBulb)

How long do gladioli bloom for?

Gladioli will only flower once per season, for around one to three weeks depending on the variety. For this reason, it's best to plant a handful of bulbs every couple of weeks in late spring/early summer for a longer-lasting display.

You can deadhead them once the flowers have bloomed, but this is purely for aesthetic reasons – it won't encourage a second flush.

  • You can give your garden springtime color by learning how to plant a bulb lasagne – our guide has all the tips you need to get started.

colorful gladioli outside summer house

A bed of vibrant gladioli will brighten up the entrance to a summer house or shed

(Image credit: iBulb)

Are gladioli toxic to dogs?

Like most bulbs, gladioli are very toxic to dogs, as well as cats. All parts of the plant are poisonous, but the bulbs themselves are particularly toxic. For this reason, if you've got a four-legged friend who loves to dig, it might be worth avoiding these blooms in your garden. If you suspect your pet is suffering from gladioli poisoning, seek advice from a vet immediately.

There is more advice on the most poisonous plants for dogs in our dedicated guide.

colorful gladioli

Although beautiful, gladioli are poisonous

(Image credit: iBulb)

Where to buy gladioli bulbs

Now you've learnt how and when to plant gladioli bulbs, you're probably eager to get hold of some for your own plot. Although you can buy them at garden centers in early spring, there are lots of places to buy them online. Our quicklinks below will help you get started.

Where to buy gladioli bulbs in the UK:

Where to buy gladioli bulbs in the US: