How to grow bulbs
Some of our favourite garden plants are bulbs, including daffodils, snowdrops, lilies and gladioli. They are planted when dormant and usually take just a few months to come into bloom. There are bulbs for every season, and for most soil types and conditions, including containers.
- Many are easy to grow
- Different types flower in every month of the year, but spring is notable
- Plant in spring, summer or autumn, depending on the type
- There are bulbs to suit all growing conditions
- Many are hardy, although some are tender
- Most are low maintenance
- They can be propagated in various ways
All you need to know
What are bulbs?
‘Bulb’ is a general term that covers four types of underground food-storage organ:
- True bulbs – these are the traditional type of bulb, usually rounded and pointed at the top, with a flat base from which the roots grow. Examples include daffodils, snowdrops and lilies.
- Corms – these look similar to bulbs, usually with one or two buds on the top, and the roots grow from the base. Examples include crocuses and gladioli.
- Tubers – these are either swollen roots, such as dahlias, or swollen stem bases, such as cyclamen.
- Rhizomes – these are swollen stems that grow horizontally, on or just below the soil surface. Examples include bearded irises, lily-of-the-valley and cannas.
All of these ‘bulbs’ differ in appearance, but essentially have a similar function – to store food when the plant goes dormant, usually after flowering.
Choosing the right bulbs
Most bulbs like a sunny spot in free-draining soil, but there are types for all situations, from damp to dry soil, full sun to deep shade.
How and what to buy
They can be bought as dormant bulbs at planting time, or growing in containers, ready to flower. Buying as bulbs is the cheaper option, but ready-planted containers provide instant colour.
They can be bought widely in garden centre and from online suppliers. Dormant bulbs should only be bought around planting time, so they don’t deteriorate in storage. Choose large, firm bulbs with no signs of damage or rot.
A few types of bulbs, such as snowdrops, can also be bought after flowering, when still in leaf (known as ‘in the green’). These specific types establish better when planted in growth, rather than when dormant. They are available from specialist suppliers.
Plants that grow from rhizomes, such as bearded irises, are usually sold in containers, ready for flowering. Tubers, such as dahlias, can be bought when dormant or in containers during the growing season.
When to plant
Planting time varies, usually depending on the flowering time.
In autumn plant:
- Spring-flowering bulbs, in September and October, but earlier is better.
- Tulips, in October and November.
- Hardy summer-flowering bulbs, in September and October.
In early spring plant:
- Tender summer-flowering bulbs, including gladioli.
In summer plant:
- Autumn-flowering bulbs, such as nerines, by late summer.
Bulbs bought in containers already in growth, or after flowering before they go dormant (‘in the green’), should be planted as quickly as possible after buying.
Where to plant
Most bulbs prefer a warm, sunny location in free-draining soil. However, specific types are suitable for other locations, including shade and dry soil.
Check the packet or plant label before buying to ensure you can provide the right growing conditions.
How to plant
Prepare your soil
Before planting, improve light or sandy soil by digging in lots of garden compost. You can always improve drainage if you have a heavy, clay soil, by digging in plenty of organic matter, such as well-rotted garden compost, leaf mould or well-rotted farmyard manure over a wider area before planting. To improve soil it is usual to apply about 5-10kg (11-22 lbs) per square metre (yard) which is generally about half to one 15L (3gallon) bucketful. We don't advise using grit anymore as so much is needed to improve drainage that it is not cost effective when compared to compost. Grit also does not help retain moisture in the soil in summer, whereas compost does this very well.
True bulbs and corms
These need to be planted quite deeply, at a depth equal to three times the bulb’s height. If planted too shallowly, they may fail to flower in subsequent years. This is particularly true of daffodils and is called blindness
In containers, bulbs can be planted less deeply and more closely packed together for greater impact, but the bulbs flower less well in the second year so are best replaced annually.
Rhizomes, such as cannas and agapanthus, usually like to be planted quite shallowly, on or just below the soil surface, depending on their preferred growing position (check packets for specific planting depths). If bought in a container, plant at the same depth it was previously growing.
Root tubers, such as dahlias and need to be planted about 15-20cm (6-8in) deep. Large-flowered begonias are planted more shallowly at 2.5-7.5cm (1-3in) Check plant labels or packets for specific planting depths.
Stem tubers, such as cyclamen should be planted near the surface. Again, check plant labels for individual instructions.
Most hardy bulbs are low maintenance, especially when growing in the ground. In containers, they just need a little extra watering and feeding.
All bulbs need plenty of water while in growth, and for six weeks after flowering until the leaves die down and they become dormant. Summer-flowering bulbs may need water during hot dry spells.
In containers, make sure bulbs don’t dry out during the growing period. When watering, water thoroughly and allow the soil to become slightly damp before watering thoroughly again. The compost should feel moist but not soggy.
See our guide to watering wisely.
To promote good flowering next year, feed the bulbs every seven to ten days with a high-potassium fertiliser such as a liquid tomato feed. Begin feeding as soon as shoots appear, and stop feeding once the foliage starts to die down at the end of the season
For bulbs in containers, start using a high-potassium liquid feed, such as tomato fertiliser, in the run-up to flowering. Continue feeding until the foliage begins to turn yellow and die back.
Vigorous summer-flowering tubers and rhizomes, such as dahlias and cannas, benefit from a high-potash liquid feed every two weeks during flowering.
Cut off spent flowers at the base of the flower stalk.
With true bulbs and corms, this won’t stimulate further flowers, but it will prevent the plant wasting energy on making seeds. Instead it will put its energy back into the bulb, for next year’s display.
With tubers and rhizomes, such as dahlias and cyclamen, regular deadheading will encourage further flowering.
Cutting back foliage
With true bulbs and corms, such as daffodils and tulips, you can cut off the dead leaves six weeks after flowering finishes. Wait until it is yellow, straw-like and no longer able to produce food for the bulb. Until this time, continue applying fertiliser and watering as above.
Also, don’t tie up or knot the leaves, as this can prevent the bulb producing flowers the following year.
Hardy bulbs can be left in the ground all year round. Those in containers should be fine too, but can be moved into an unheated greenhouse or cold frame in colder regions which are subject to hard frosts.
Tender, half-hardy and borderline-hardy plants, such as cannas, agapanthus, gladioli and dahlias, can be grown in containers and brought indoors over winter. If you live in a mild area, you could risk leaving them in the ground over winter, covering them with a 20-25cm (8-10in) layer of insulating mulch and removing the mulch in spring as they come into growth.This is only possible on a light free-draining soil, as a heavier clay soil will become too wet over winter and cause the plants to rot. In this instance it is best to grow these plants in containers.
Some bulbs such as tulips, prefer to be kept dry when they are dormant in summer. To provide these conditions they are best lifted, dried off and then stored until autumn, when they can be planted out once more
To lift and store true bulbs and corms:
- Wait until the foliage has died down, then carefully dig up and clean off the loose soil from the bulbs.
- Trim off the roots and the outer layers of loose, flaking tunic.
- Only keep healthy bulbs of a good size as these will be most likely to flower the following year– discard damaged or diseased bulbs.
- Lay the bulbs on a tray to dry for at least 24 hours, to help prevent fungal rots developing in storage.
- Put the bulbs in labelled paper bags or nets and store in a dry, cool place.
Caring for older plants
Clump-forming bulbs can become congested over time, which can reduce flowering. Divide the clumps every few years to keep them vigorous and flowering well.
True bulbs and corms
These are easy to propagate, but require patience. Most take two to seven years to reach flowering stage from seeds or from chipping bulbs or rooting bulb scales.
Those that form clumps, such as snowdrops and grape hyacinths, can be dug up after flowering, split into smaller groups and replanted to establish new colonies. These should settle in quickly and flower the following year.
These fleshy underground stems are very easy to propagate by cutting the rhizome into sections. Make sure each section has roots and buds, often referred to as 'eyes'. Replant these at the same depth as the original plant.
Fleshy root tubers, such as dahlias, can usually be propagated in spring by division or by taking basal shoot cuttings. When dividing it is important that each piece has buds or shoots developing on it otherwise the division may not be able to produce a new plant.
Bulbs are relatively trouble free. However, if planted at the wrong depth, they may fail to flower in subsequent years.
Before storing bulbs, discard any that are damaged or diseased. Also discard any with yellow mottled foliage, as this usually indicates an incurable virus infection.
Some bulbs can become invasive, and spring is a good time to remove those that have spread too far.
Pests that can attack bulbs include:
- Slugs and snails, which may eat young foliage and flowers.
- Squirrels, which may dig up and eat bulbs including crocuses and tulips.
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