Flower Bulbs 101: Planting for Year-Round Bloom

Flower bulbs 101 explains planting for year-round bloom, so something opens in every month from the first crocus to the last dahlia.

Plant spring-flowering bulbs in autumn at about three times their own height, pointed end up, in soil that drains well. Plant summer bulbs, corms and tubers after the last frost. Get depth, drainage and chill right and most bulbs flower reliably; get them wrong and you see leaves without flowers or soft, rotted lumps. This guide covers the four storage types, exact depths and spacing, chill requirements, aftercare and a month-by-month sequence.

It sits within the Flower Gardening guides. Pair it with the Seasonal Planting Calendar for local dates, the Cutting Garden for bouquet planning, and Annuals vs Perennials for filling gaps once the bulb foliage fades.

At a glance

Four storage types, four rules

A true bulb (tulip, daffodil, allium, lily) is a stack of fleshy scales around a embryonic flower, and it needs depth and drainage. A corm (crocus, gladiolus, freesia) is a solid swollen stem base that’s used up each year and replaced by a new corm on top of the old one, which is why gladiolus lose vigour if planted too shallow. A tuber (dahlia, tuberous begonia, anemone) stores energy in swollen roots or stems and sprouts from visible eyes. A rhizome (iris, canna) is a thick horizontal stem that wants its top at or near the surface.

The depth rule of thumb, three times the bulb’s height, protects against frost, drying out and tipping over. Adjust it to the soil: in heavy clay plant 2 to 3 cm (1 in) shallower, since deep clay stays cold and wet in spring. In sandy soil plant slightly deeper. If you plant a bulb upside down it usually still finds its way up, though it spends energy doing so and flowers later.

Chill requirements by climate

Tulips and hyacinths evolved with cold winters followed by dry summers. They set their flower buds properly only after about 12 to 16 weeks with soil temperatures below roughly 9°C (48°F). Daffodils need less and cope with milder winters, which is why they naturalise across a wider range. Crocus and snowdrops are also very reliable in cold zones.

• Cold winters (below freezing for weeks): plant tulips in late autumn once soil is below about 10°C (50°F), and they chill in place.
• Mild winters (rarely below 0°C or 32°F): buy tulips and hyacinths early, store them in a paper bag in the fridge at 2 to 5°C (35 to 41°F) for 12 to 16 weeks, then plant in midwinter and treat them as annuals.
• Hot, frost-free climates: choose bulbs that need no chill, such as paperwhite narcissus, amaryllis (Hippeastrum), freesia, ranunculus and tuberose.

How to plant a bed of bulbs

1. Choose firm bulbs. They should feel heavy, with no soft spots or mould. Larger bulbs generally flower better than small ones of the same type.
2. Check drainage. Fill a 30 cm (12 in) hole with water. If it still holds water after 4 hours, plant in a raised bed or add grit, since winter wet is the main cause of bulb rot. Our soil type guide explains the jar test.
3. Dig to the right depth. Measure from the base of the bulb. Dig a wide hole for a group instead of one hole per bulb.
4. Set bulbs in clumps. Groups of 7 to 15 look better than single bulbs in a row. Space them about two bulb widths apart.
5. Backfill and water once. Water in to settle the soil and start root growth, then leave autumn rain to do the rest.
6. Protect from squirrels and voles. Lay wire mesh with a 1.5 cm (0.5 in) grid over the soil, or plant tulips inside a mesh basket. Daffodils, alliums and snowdrops are usually left alone.

A bloom calendar from late winter to autumn

Timing below suits a temperate Northern Hemisphere garden; shift by 2 to 4 weeks for colder or warmer sites, and by six months in the Southern Hemisphere.

Stagger gladiolus corms every 2 weeks from spring until about 90 days before your first autumn frost for a continuous cutting supply. Colchicum (often sold as autumn crocus) is highly toxic if eaten, so site it away from children and grazing animals.

After flowering

Bulbs flower from stored energy, then refill the store through their leaves. Remove spent flower heads so seed doesn’t drain the bulb, but leave the foliage until it turns yellow, normally about 6 weeks after flowering. Don’t tie or plait the leaves, since that cuts the light they can catch. A feed high in potassium (such as a tomato fertiliser) at flower fade helps, while high nitrogen encourages leaves at the expense of next year’s flowers.

Hide fading leaves by planting bulbs among emerging perennials such as hostas or hardy geraniums. In warm climates, or if tulips decline fast, lift them when the leaves die, dry them in shade and store in a cool, ventilated place. Lift dahlias and canna after the first frost blackens the foliage in zones where the ground freezes, and store the tubers in barely damp bark or sawdust at 5 to 10°C (41 to 50°F).

Troubleshooting

How flower bulbs bloom through the year

Crocus, daffodil and tulip need a cold winter and a well-drained bed, because wet clay encourages rot and kills the bulb. Grit and compost improve drainage in heavy soil, and a sunny spot warms the bulb and supports flowers. Daffodil tolerates deer and rabbit, while tulip attracts them, so netting protects your display.

Leaves feed the bulb after flowering, which means you shouldn’t cut them until they’ve yellowed. Potash and bone meal support root growth at planting, but fresh manure burns bulbs and causes disease. Allium, lily and dahlia carry colour into summer, and iris and hyacinth fill spring with scent. When should you plant? Plant crocus and daffodil in early autumn and tulip a little later when soil temperature falls, because warm ground encourages fungus. Your extension service can recommend bulbs suited to your frost dates.

How flower bulbs 101 keeps colour going year round

Crocus, daffodil and tulip need a cold winter and a well-drained bed, because wet clay encourages rot and kills the bulb within weeks. Grit and compost improve drainage in heavy soil, and a sunny spot warms the bulb and supports flowers in March and April. Daffodil tolerates deer and rabbit, while tulip attracts them, so netting or wire mesh protects a tulip display.

Planting depth should be three times the bulb’s height, so a 5 cm tulip needs a hole 15 cm deep, and frost can’t reach it there. Potash and bone meal support root growth at planting, but fresh manure burns bulbs and causes fungus. Leaves feed the bulb after flowering, which means you shouldn’t cut daffodil foliage until it has yellowed after 6 weeks. Allium, lily and dahlia carry colour into summer, and hyacinth and iris fill spring with scent that attracts bee and hoverfly. Squirrel digs up crocus, so a layer of grit or chicken wire controls losses. Plant crocus and daffodil in early autumn, and tulip a little later when soil temperature falls below 10°C, because warm ground encourages disease. Your extension service can recommend bulbs suited to your frost dates, and the annuals and perennials guide shows how to fill the gaps in summer.

Common mistakes

• Planting too shallow. Bulbs near the surface split into small offsets that don’t flower and are more exposed to frost heave. Measure to the base and follow the 3 times rule.
• Cutting foliage while green. The bulb loses its refill, so next year brings fewer flowers. Wait until the leaves are yellow and tug away easily.
• Planting too early in warm autumns. Tulips planted into warm soil are more prone to a fungal disease called tulip fire. Wait until soil is below about 10°C (50°F).
• Forgetting drainage. Bulbs tolerate cold but not standing water, so heavy soil needs raised beds or grit.
• Skipping the fridge chill in mild climates. Without it tulips make short stems and sparse flowers. Chill for the full 12 to 16 weeks.

For summer tubers, see How to Grow Dahlias.

Next steps

Use the Seasonal Planting Calendar to find your local planting window, then add bee-friendly crocus and alliums using Flowers That Attract Pollinators. For a border that stays tidy once leaves yellow, try Low-Maintenance Flower Borders. Return to the Flower Gardening guides for more.