Monty Don’s tips on planting summer bulbs

With the glorious arrival of spring, it’s time to plan for warmer months ahead by planting summer bulbs. Celebrity gardening expert Monty Don has a particular fondness for these diverse flowers, which add invaluable color and scent to the garden.

‘The best summer bulbs never really get the attention that they deserve but it is a pity not to explore the full range of bulbous possibilities in the summer months,’ he says in his book The Complete Gardener (opens in new tab).

While spring bulbs are planted out in the fall, Don explains that most summer bulbs must be planted in the spring. ‘Summer flowering bulbs have evolved to survive winter cold and drought, and they tend to come from parts of the globe where summers are warm and moist,’ he says.

For example, lilies are native to Asia, where monsoon season provides water for the year, while gladioli and eucomis come from the Eastern Cape in South Africa, which has summer rainfall. ‘Knowing this, it makes sense to plant summer bulbs in the spring as the soil begins to warm up, in tune with the rhythm of their growth,’ says Don.

Planting summer bulbs

While summer bulbs can be planted in the ground, Don loves to plant them in containers to better control their soil conditions and to ensure a seamless succession of color in the garden.

‘Having plants in pots – that have their moment in the sun so to speak – and then can be pushed sideways to let something else come in, it adds a real level of flexibility to the garden,’ he says in an episode of BBC's Gardener’s World (opens in new tab). 

See: Container gardening ideas – ways to create a lush oasis in the smallest of spaces

Perhaps the most important consideration when planting summer bulbs is to provide enough drainage. ‘With most bulbs you can never have too much drainage – they will grow the better for it,’ says Don.

For this reason, he prefers to use terracotta pots, which drain better than many other container types. However, he acknowledges that most of us don’t have an endless supply of them left lying around to dedicate to summer bulbs – ‘your tulip pots will be occupied for another couple of months'.

To solve this issue, in his video, Don revealed a brilliant tip for doubling up pots for both spring and summer flowering bulbs, demonstrating planting gladioli into a lattice pot used for subaquatic plants. ‘They can drain well, the roots can come out if they want; but you can do it in just a normal plastic pot,’ he explains.

‘Then after the tulips are finished, they can come out and can dry off – and then I will plunge these into that pot, and when the gladioli are finished in September or October, they can come out and the tulips can be planted.’ Following this method will mean your pots will be in constant use through the year.

Whatever you plant your summer bulbs in, it’s essential to have the right compost that provides effective drainage. ‘Add a bit of grit to the compost – and you can’t really overdo this so don’t be coy about it,’ says Don.

The depth you plant your bulbs is also key. ‘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.'

Finish with a good watering. ‘By watering them it will trigger them into growth,’ he says.

See: Monty Don's top vegetable gardening tips

Monty Don's best summer bulbs to grow

This list of the best summer bulbs to plant out now will ensure beautiful garden color and fragrance.

1. Lilies

Don loves to grow lilies for both their beauty and heady fragrance. ‘I think it is essential to garden for all the senses,' he says.

Lilies prefer slightly acidic soil, so if you have alkaline soil, then it's best to grow them in large pots, and provide good drainage.

2. Agapanthus

Agapanthus have fabulous large globe-shaped flower heads, usually in purple, blue or white.

'To get agapanthus to grow, you do need to restrict its roots,' says Don in an episode of BBC Gardener's World. 'You do need to make sure they have very good drainage. But also you do need to make sure they are fed. So it’s getting a balance between enough food and water but not too much.'

He advises adding a good amount of grit to the compost and putting three plants into a pot that's just big enough. 'There is no point in putting an agapanthus into too big a pot, because all you’ll get is lots of leaves and no flowers,' he says.

'Put them somewhere in maximum sunlight, water them once a week, feed them once every two or three weeks, and then at the end of the summer, take them somewhere cool – it doesn’t have to be warm at all, but just frost free.'

3. Dahlias

In his book The Complete Gardener, Don reveals he loves everything about dahlias. ‘We have them singly in posts, as part of big containers growing alongside cannas, cosmos, bidens, petunias and nasturtiums, and in borders. All add immeasurably to the pleasure and beauty of the garden and I cannot conceive of being without them.’

See: How to grow dahlias – a step-by-step guide

He begins the dahlia year in March, taking out the stored tubers that have been overwintering. He inspects them to discard any rotten or shriveled specimens, puts a few onto the hot bench to be forced for cuttings, then sets the rest out into to cold frame ‘to gently ease into growth.’ The dahlias are then planted out in May.

4. Crocosmias

Crocosmias are easy summer bulbs – or 'corns' – to grow and Don likes them for the structure they add to the garden. ‘Crocosmias are a very important part of the high-summer garden, although their large strap-like leaves give body and form for weeks before the flowers emerge,’ he says.

Don finds he needs to give the plants eary support so they they do not ‘flop too much over their neighbors'.

As crocosmias spread and grow very large, he recommends lifting large clumps in early spring, separating them apart and replanting them in smaller groups. ‘They will respond with increased vigor and flowers,’ he says.

See: How to plant roses – an essential guide

5. Alliums

Alliums are an essential flower for any garden, as they pop up among borders to add color and structure, and are bee and butterfly magnets.

Unlike most summer bulbs, alliums are best planted in the fall. The exception is A. sphaerocephalon, which will flower into September and can be planted in spring. However, you can buy potted alliums to fill your borders with this summer.

See: Monty Don's beautiful Longmeadow garden in Herefordshire

'Alliums are true bulbs and fully paid up members of the onion family,' says Don in The Complete Gardener. Most will obligingly reappear year after year – often too obligingly as they will spread dramatically by seed as well as by new bulbs.'