What Are Summer Bulbs?
Summer bulbs are a fantastic way to introduce a succession of vibrant colour and diverse textures to your garden during the warmer months. Unlike spring-flowering bulbs which are typically planted in autumn, summer bulbs are planted in the spring after the last frost has passed. They thrive in warmer soil, developing quickly to produce spectacular flowers from early summer through to autumn.
- Summer bulbs are planted in spring for summer blooms.
- They require warmer soil to establish.
- Offer a diverse range of colours and forms.
- Extend garden colour well into autumn.
The term 'bulb' is often used loosely in horticulture to include tubers, corms, and rhizomes, all of which are underground storage organs capable of producing a new plant. These 'bulbs' lie dormant until conditions are favourable, typically spring, before sending up shoots and roots. They offer a unique gardening experience, often providing some of the most exotic and eye-catching flowers available.
From the statuesque spikes of gladioli to the elegant trumpet shapes of lilies and the architectural spheres of allium, the variety is immense. They are perfect for adding drama to borders, filling containers, or even naturalising in lawns for a wilder effect. Understanding their specific needs ensures you get the most impressive display year after year.
Choosing Your Summer Bulbs
Selecting the right summer bulbs depends on your garden's conditions and the aesthetic you wish to achieve. Consider the height, bloom time, and colour palette. For striking vertical accents, gladioli and delphiniums (though technically tubers) are excellent choices. For large, dramatic blooms, dahlias and lilies are unparalleled. For intricate, architectural interest, consider alliums, which also come in various sizes and shades of purple and white.
When purchasing, always look for plump, firm bulbs free from mould or damage. Reputable suppliers will offer a wide selection and provide clear planting instructions. Many summer bulbs are tender and may need to be lifted and stored over winter in colder climates, or treated as annuals for a guaranteed display each year.
Inspect bulbs thoroughly before planting. Healthy bulbs are firm and plump, indicating good stored energy for growth. Avoid any that are soft, discoloured, or show signs of rot.
When to Plant Summer Bulbs
The crucial planting window for most summer bulbs is spring, after the threat of hard frost has subsided and the soil has begun to warm up. In the UK, this generally means from late March through to May. Planting too early can lead to rot in cold, damp soil, while planting too late may mean missing the peak flowering period.
Some bulbs, like dahlias, benefit from being 'chitted' indoors a few weeks before planting. This involves placing them in a shallow tray of compost in a frost-free environment to encourage early sprouting. Tender bulbs like cannas, eucomis, and tuberous begonias should definitely be planted after all danger of frost has passed, often a little later in May, or started under cover.
Soil temperature is a more reliable indicator than the calendar. Aim for a minimum soil temperature of 10-12°C (50-54°F) before planting directly into the ground. If you're uncertain about your local conditions, it's always safer to wait a little longer.
Understanding Summer Bulb Types
The category of summer bulbs encompasses a wide array of plant types, each with unique characteristics:
- True Bulbs: Like lilies and tulips (though tulips are often spring-flowering, some varieties extend their season).
- Corms: Solid, rounded underground stems with buds, such as gladioli and crocus (autumn-flowering types).
- Tubers: Swollen underground stems or roots that store nutrients, including dahlias, begonias, and anemones.
- Rhizomes: Horizontal underground stems from which new shoots and roots grow, like irises and cannas.
Knowing the type helps in understanding its specific cultivation needs, such as planting depth and winter storage requirements.
How to Plant Summer Bulbs
Correct planting technique is fundamental for successful summer bulb growth. While specific depths and spacings can vary between species, some general principles apply. Most summer bulbs prefer well-drained soil and a sunny to partially shaded location, depending on the variety. Poor drainage is a common cause of failure, leading to rot.
Prepare the planting area by digging in organic matter, such as compost or well-rotted manure, to improve soil structure and fertility. If your soil is heavy clay, consider adding grit or sand to enhance drainage. For bulbs that require specific orientation, such as those with a distinct top and bottom (e.g., lilies), ensure they are planted the correct way up. The pointed end or where the stem emerged is usually the top.
Planting Depths and Spacing
A general rule of thumb for many summer bulbs is to plant them at a depth approximately two to three times their height. For instance, larger bulbs like dahlias might be planted about 10-15 cm deep, and smaller ones like gladioli corms can be planted at 8-10 cm. Always check the specific recommendations for the bulb variety you are planting.
Spacing is also important to allow plants room to grow and develop without competing excessively for light, water, and nutrients. For smaller bulbs, spacing of 10-15 cm apart is common. Taller, more substantial plants like lilies or dahlias may require 30-45 cm or more. Planting in groups or drifts often creates a more impactful display than scattering them individually.
Planting Tulip Bulbs: For those that flower in late spring but are often considered in summer bulb discussions, plant tulip bulbs around 15 cm deep and 10 cm apart in well-drained soil, ideally in a sunny spot.
Container Planting for Summer Bulbs
Summer bulbs are exceptionally well-suited for container gardening, offering flexibility in placement and the ability to control growing conditions precisely. Use pots with drainage holes and a good quality, free-draining compost. A mix of potting compost with added perlite or grit is ideal.
Plant bulbs at the recommended depth, ensuring they do not touch the sides or bottom of the pot directly. Water thoroughly after planting. Keep pots in a sunny, sheltered location. For tender varieties, containers make it easier to move them to a frost-free spot for winter storage.
When planting gladioli, ensure the corms are oriented correctly with the pointed end upwards. Plant them about 10-15 cm deep and 10 cm apart for striking vertical displays. They perform well in both borders and containers.
For a continuous show, stagger plantings of bulbs with similar needs by a couple of weeks.
Consider planting depth carefully. Too shallow and they may dry out or be damaged by weather; too deep and they may struggle to emerge. Always refer to supplier recommendations for precise measurements.
Caring for Your Summer Bulbs
Once planted, summer bulbs require consistent care to ensure they reach their full potential. Watering is critical, especially during dry spells. While they need moisture to grow and flower, they do not tolerate waterlogged conditions. Ensure the soil remains consistently moist but not saturated.
Regular feeding can significantly boost flowering. A balanced liquid feed or a slow-release fertiliser applied in spring when growth appears, and again just before flowering, will provide the necessary nutrients. For bulbs grown in containers, feeding may be required more frequently due to nutrients leaching out with regular watering.
Supporting Taller Varieties
Many summer-flowering bulbs, such as gladioli, lilies, and dahlias, grow tall and can be susceptible to wind damage or bending over. Providing support early on is advisable. Use sturdy stakes, canes, or purpose-made plant supports inserted into the soil at planting time or when the plants are about a third of their mature height. Tie stems loosely to the supports as the plant grows.
For ornamental onions (allium), while many are self-supporting, taller varieties might benefit from a discreet stake in exposed locations. Ensuring good air circulation around plants, by maintaining correct spacing, also helps to prevent fungal diseases.
Caring for Lilies: Lilies prefer well-drained soil and full sun to partial shade. Water them regularly, especially when in bud and bloom. Deadhead spent flowers to encourage the plant to put energy into the bulb rather than seed production, but allow the foliage to die back naturally in autumn to feed the bulb for next year.
Dealing with Pests and Diseases
Summer bulbs can be targets for various pests and diseases. Slugs and snails are notorious for damaging emerging shoots and foliage. Use appropriate deterrents, such as slug pellets (used cautiously), barriers, or encourage natural predators. Vine weevils can attack the roots of plants in containers, causing wilting and collapse; biological controls or specific treatments may be necessary.
Fungal diseases, like botrytis (grey mould), can affect foliage and flowers, particularly in humid conditions. Ensuring good air circulation, avoiding overhead watering, and promptly removing any affected plant material are key preventative measures. Proper soil preparation and choosing disease-resistant varieties where possible also contribute to a healthier display.
Overwintering Tender Bulbs
Many of the most spectacular summer bulbs, such as dahlias, cannas, and begonias, are tender and will not survive a harsh winter outdoors in the UK. To save them for the following year, they need to be lifted and stored.
After the first autumn frost has blackened the foliage, carefully dig up the bulbs or tubers. Allow them to dry slightly in a cool, airy place, then remove excess soil. Store them in trays filled with dry peat, sand, or newspaper in a frost-free location, such as a shed or garage. Check them periodically for any signs of rot or drying out.
Lift tender bulbs at the right time. Wait until the foliage has been killed by frost, but before the ground freezes solid, to ensure the storage organs are mature enough to survive.
Alternatives and Companion Planting
While summer bulbs offer instant impact, integrating them with other plants can enhance their display and provide continuous interest throughout the season. Perennial plants that bloom later in summer can complement the fading flowers of bulbs, ensuring your garden remains vibrant. Consider plants like Echinacea, Rudbeckia, or Asters which bloom into autumn.
For smaller gardens or those seeking a more naturalistic look, consider planting summer bulbs amongst ground cover plants or low-growing perennials. This can help suppress weeds, retain soil moisture, and provide a softer backdrop for the bolder blooms. Bluebells, though typically spring-flowering, can sometimes naturalise in dappled shade and provide an early carpet of colour before many summer bulbs emerge.
Companion Planting for Summer Bulbs
Companion planting can offer more than just aesthetic appeal; it can also provide practical benefits. For instance, planting strong-smelling herbs near your bulbs can help deter certain pests. Some gardeners find that planting aromatic plants like rosemary or lavender nearby can help ward off aphids and other sap-sucking insects.
When planting bulbs in containers, consider mixing them with trailing or low-growing annuals. This fills any gaps that appear as the bulb foliage dies back and creates a fuller, more layered look. For example, planting gladioli alongside trailing petunias or lobelia can provide a beautiful contrast in form and colour.
Companion Planting with Alliums: Allium flowers are known for their striking spherical shapes and can be planted alongside lower-growing plants like perennial salvias or catmint. These companions provide a colourful, textured base that highlights the allium's upright grandeur and can also help mask the allium's foliage as it yellows after flowering.
Annuals vs. Perennial Bulbs
The choice between annual and perennial summer bulbs often depends on climate and gardener preference. Tender bulbs like dahlias, cannas, and gladioli are often treated as annuals in colder regions to guarantee a spectacular show, although they can be overwintered with care. This approach avoids the need for winter storage and ensures vigorous new growth each year.
Hardy bulbs, such as certain varieties of lilies and alliums, are perennial and will return year after year, often increasing in number. These are a more sustainable choice for long-term garden planning. Snowdrops and crocuses, while primarily spring bloomers, are also examples of hardy bulbs that naturalise readily. For a truly low-maintenance, long-term summer display, focus on perennial varieties and suitable companion plants.
Choosing Lilies for Summer Blooms: Lilies are a classic perennial summer bulb offering diverse colours and forms. Plant lily bulbs in well-drained soil, ensuring the bulb is planted deep enough to protect the base from sun scorch, typically 15-20 cm deep, with the pointed end up. They thrive in full sun to partial shade and will provide impressive blooms for years.
Extend your summer colour with successive planting. Plant different varieties of summer bulbs with overlapping bloom times, or stagger plantings of the same type by a few weeks, to ensure a continuous display from early summer through to autumn.