7 Best Summer-Flowering Bulbs and Tubers for a Colourful Garden

Get your hands dirty briefly in April – and your garden will burst into colour all summer long.

With no bare patches at all.

Every year, many amateur gardeners are frustrated by gaps in their flower beds: blooms have already faded in one spot, while another area has yet to produce anything. Choosing the right summer-flowering bulbs and tubers in April is a targeted way to avoid this issue. The result is a bed in flower from June well into autumn – full, colourful and uninterrupted.

Why April is the ideal month for summer-flowering bulbs

In April, soil conditions and weather generally work together perfectly. The ground still retains plenty of moisture from winter, but it is no longer constantly drying out. At the same time, temperatures rise enough for bulbs and tubers to begin growing quickly.

The combination of residual soil moisture and increasingly warm temperatures encourages a strong root system – the most important foundation for a long summer flowering season.

Planting now gives plants a head start: they establish robust roots early and cope far better with dry spells in high summer. This also reduces the need for watering, which is a genuine advantage in areas subject to water restrictions.

Although the main planting period for summer bulbs runs from March to May, April is considered the best compromise. Frost is rarely still present in the soil, the ground is noticeably warmer, and plants can comfortably flower from around June until October.

April is particularly reliable in cooler places where late frosts are possible, such as upland areas and higher-altitude regions. In milder parts of the country or wine-growing areas, planting can begin at the very start of the month. This makes it easy to adapt the timing to local conditions.

The 7 best tubers and bulbs for a summer bed without gaps

This selection includes a wide range of heights, flower shapes and colours. Planted together, they create a relay of flowering from June far into autumn.

Dahlias: an explosion of colour into autumn

Dahlias are planted as tubers and grow quickly once shoots emerge. They usually flower from high summer through to October, offering almost every look imaginable: small pom-poms, enormous dinner-plate blooms, cactus forms, simple flowers for insects, and colours ranging from pastels to neon shades.

They prefer rich, loose soil and a sunny position. Taller varieties need staking, otherwise the next summer thunderstorm can simply flatten them. Regularly removing faded flower heads encourages fresh buds to keep appearing.

Lilies: elegant, fragrant stars for the middle or back of the border

Lilies add height, structure and, depending on the variety, a powerful fragrance to a border. They generally flower between June and August. Their upright stems make them well suited to the middle or rear of a planting scheme.

They need deep, loose soil that is fairly rich in humus, and do best with their roots lightly shaded while the flowering stems are in sunshine. Planted in small groups, they make a much stronger impact than isolated individual stems.

Tuberous begonias: colour for shady corners

Tuberous begonias are ideal for partially shaded to shady beds, underplanting and large containers. Usually flowering from July into autumn, they brighten even darker areas with vivid red, orange, pink, yellow or white blooms.

They favour a fertile, loose growing medium that must never dry out completely but should not become waterlogged either. In borders, they work particularly well with plants such as hostas or ferns, which have similar needs for moisture and shade.

Gladioli: striking flower spikes for summer

Gladioli are the classic cut flowers from grandmother's garden – and they are currently enjoying a comeback. Their tall, slender flower spikes provide bold summer accents, especially when planted in rows or larger groups.

Planting a new row of gladioli every ten days extends the flowering display over many weeks. In exposed or windy gardens, their tall stems must be supported with canes or other stakes, as they can snap easily.

Canna: tropical atmosphere in the garden

Canna, also known as canna lily, creates an almost tropical feel with its large, often variegated leaves and bright flowers. It loves full sun, warmth, and nutrient-rich, well-drained soil.

Its distinctive flowers appear from roughly June to August, but its luxuriant foliage remains impressive even when it is not in bloom. Pairing it with warm shades such as orange, red and yellow creates a real holiday mood in the border.

Crocosmia: delicate sprays of fire

Crocosmia, often also called montbretia, produces delicate, arching sprays of orange, red or yellow flowers. It is less imposing than canna or dahlias, but adds plenty of movement to the planting.

It enjoys sunny, free-draining positions and works well at the front or centre of a border. Its flowers are regarded as magnets for bees and other insects.

Agapanthus: architectural flower spheres

Agapanthus, commonly called African lily, attracts attention with round flower heads in blue or white held on long stems. Flowering from June to August, it gives beds and containers a crisp, almost architectural structure.

It likes warmth, sunshine and soil that is relatively lean rather than overly rich. It can overwinter in borders in mild areas, but growing it in a container is the safer option elsewhere. The plant can then be moved into a frost-free garage or cellar.

How to plant summer-flowering bulbs correctly

The rule of thumb is to plant at a depth of around two and a half to three times the height of the bulb or tuber, allow the spacing stated for the variety, and always use well-drained soil.

• Loosen the soil and improve heavy ground with sand or compost.
• Dig planting holes deep enough to give a planting depth of 2.5–3 times the height of the bulb or tuber.
• Position the pointed end upwards, refill loosely with soil and firm gently.
• Water generously so that the soil settles around the plant.
• Apply a layer of bark mulch or similar material to retain moisture.
• Where necessary, add a support cane at planting time for tall varieties such as gladioli, dahlias and canna.
• If late frosts are forecast, protect young shoots with horticultural fleece or an upturned bucket.

Planning borders cleverly: where each plant has the greatest impact

A well-considered arrangement prevents tall plants from overwhelming smaller neighbours. Deliberately graduating the heights also makes the border more interesting.

Border area	Suitable plants	Effect
Back	Lilies, agapanthus, tall dahlias, canna	Height, structure, bold blocks of colour
Middle	Medium-height dahlias, gladioli, crocosmia	Colourful bands of flowers, movement
Front	Tuberous begonias, low dahlias, crocosmia	Dense cushions of flowers, a closed border edge

Adding perennials such as coneflower, coreopsis or gaura among the tubers increases the density of the bed and fills small gaps without crowding the summer bulbs. Low ground-covering plants such as alyssum, green alkanet or lamium are suitable for the very front.

Combining colours and textures effectively

Visually, a border depends above all on contrasts. The fine flower spikes of gladioli combine beautifully with the rounded heads of dahlias. The warm shades of canna and crocosmia bring energy, while white or blue agapanthus blooms create calming areas.

In shaded spaces, tuberous begonias, hostas and heucheras make an almost painterly combination: large leaves, vivid flowers and foliage colours ranging from green to deep purple. In full sun, canna and crocosmia pair exceptionally well with delicate grasses such as fountain grass, giving the whole display a lighter, more natural appearance.

Common planting mistakes – and how to avoid them

What many people underestimate is that waterlogging is the most frequent reason bulbs and tubers rot. If water remains in the bed for a long time after rain, the soil urgently needs improving. Sand, grit and compost can solve the problem.

Planting too shallowly is also an issue. Dahlias tubers or lily bulbs placed only just beneath the surface dry out more easily or can be damaged by frost. The guideline of two and a half to three times their height is genuinely worthwhile here.

When watering, soak plants thoroughly after planting, then water less often but more deeply later on. Constant wetness encourages fungal diseases and rotting tubers. A good mulch reduces evaporation and keeps the soil moist for longer.

Practical guidance on care, storage and winter protection

Many of these plants are not fully hardy. Dahlias, gladioli and canna should be lifted after the first light frost. Store the tubers and rhizomes in boxes with a little dry soil, sand or sawdust in a cool, frost-free place.

Container-grown agapanthus can remain in its pot, but needs a bright, frost-free space where the temperature stays slightly above freezing. Crocosmia usually survives in the ground in mild locations when protected by a thick layer of mulch; in harsher areas, it is also worth providing light winter protection.

Once these routines become familiar, you can enjoy an almost self-managing summer garden for years: plant in April, enjoy it through summer, and do a little tidying in autumn. With the right mix of dahlias, lilies, tuberous begonias, gladioli, canna, crocosmia and agapanthus, borders look full, floriferous and remarkably professional – entirely without horticultural training.