Gardens Illustrated

Forcing bulbs: what does forcing bulbs mean and how to do it

Published: August 1, 2020 at 5:01 pm

Forcing bulbs is a way to manipulate spring bulbs so that they flower early, bringing a much-need burst of colour into the home during the winter months, when very little is happening in the garden. Try these bulb combinations to learn how to force bulbs yourself

Forcing bulbs allows you to enjoy the colours of spring bulbs in December. The method involves careful preparation of bulbs to give them a long-enough period in cool, dark conditions before bringing them indoors to flower. Narcissus 'Paper White' and oriental hyacinths are traditional choices for 'forcing' but you can prepare and grow a wide variety of garden bulbs indoors, from muscari and scillas, to iris and crocus, to create something unique (see container combinations below).


What is meant by 'forcing bulbs'?

Forcing bulbs, simply requires mimicking the cold, dark conditions of winter (ideally at a temperature of between 1.5ºC and 10ºC) for around ten weeks to give the roots time to develop, before bringing them indoors where the warmth (above 15ºC) and light will fool the bulbs that spring has arrived so that they sprout and bloom around four to six weeks early. The forced hyacinths that are sold commercially to flower in time for Christmas have been pre-chilled. You can do this yourself by keeping the bulbs for 12 weeks in the bottom of the fridge, but not all bulbs need this.

Three forced bulb combinations for indoor displays

Yellow, blue and scented

Muscari macrocarpum 'Golden Fragrance', Scilla messeniaca, Iris reticulata 'Katharine Hodgkin', Cornus mas and Corylus avellana
Muscari macrocarpum 'Golden Fragrance', Scilla messeniaca, Iris reticulata 'Katharine Hodgkin', Cornus mas and Corylus avellana

Muscari and scillas bulbs have been used here to make the most of their fragrance. In late winter they will fill a room with their sweet, musk perfume, conjuring a warm Mediterranean spring that is still months (and miles) away. The tight flowers of Cornus mas naturally occur in the same habitat as both the muscari and the iris, so it's a good choice for the twig supports. The starting point for this display was the baby blue on the enamel flour bin.

Bulb container, cultivation and care

If you're using a deep pot like this one, make sure you have drainage hols in the bottom and fill the bottom third with crocs. Good drainage is crucial for bulbs. Using 3-6mm grit, put a thick layer in the bottom of the pot and then fill with a gritty loam-based compost. Position all the bulbs on the same layer with their crowns just below the surface. The planter should be fairly full, but the bulbs should not touch. Water once as you plant then leave somewhere dark, such as a covered cold frame or an unheated shed or garage, for about a month, checking regularly for signs of pest damage. Bulbs are vulnerable in small pots so protect from frost – a temperature of between 1.5-10ºC is ideal. Once foliage begins to grow, move them somewhere cool before bringing into the warmth and resuming careful watering

Group together

Iris reticulata 'Katharine Hodgkin', Crocus chrysanthus 'Romance', Muscari armeniacum and Anemone blanda 'Charmer'
Iris reticulata 'Katharine Hodgkin', Crocus chrysanthus 'Romance', Muscari armeniacum and Anemone blanda 'Charmer'

A group of pots with forced bulbs works particularly well for table decorations. In this display, a decorative pot has been used to emphasise the ornate veining of the iris and a simple rustic terracotta pot for the anemone and the muscari bulbs. The unusual pale yellow of the crocus combines well with the aqua and yellow flowers of the iris. Dress your bulb containers with a layer of grit to finish off the look.

Container cultivation and care

Start with clean pots and healthy bulbs. Fat and firm is favourable; anything small or soft is suspect. With displays like this, it can be a good idea to initially plant all the bulbs in small pots, then replant them in the pretty containers as they bud and then dressed them with grit. Remember to leave a little space at the top to enable easy watering. Once in flower, you can extend the flowering period by placing them in a cool location overnight.

Woodland scene

Anemone blanda 'Charmer', Galanthus Viridapice, Crocus Tommasinianus 'Ruby Giant' and Cyclamen coum album
Anemone blanda 'Charmer', Galanthus Viridapice, Crocus Tommasinianus 'Ruby Giant' and Cyclamen coum album

Woodlands offer the very earliest spring flowers as the bulbs have evolved to jump in and flower before the leaf canopy closes above them. Think of snowdrops, cyclamen and anemones that are often found mingling together on the forest floor in the eastern Mediterranean. Here the shiny, round leaves of the cyclamen bring texture and reflective light to the planting. While the large, open flowers of the crocus add a dramatic shot of vivid, ruby purple. The upright linear foliage is a good contrast and adds height. This display has been planted into a homemade log planter and the texture of the bark (silver birch) gives the plants an immediate context. Tuck moss in between the plants for a finishing woodland touch.

Container, cultivation and care

Pot up a few of each bulb into little pots of the loam-based soil mix first and put them in the cold frame. The anemone corms need to be soaked overnight before planting. These bulbs do not need pre-chilling to flower but ten to 12 weeks in the cold is required to establish good roots. Put the look together once they start into growth. It is best to plant the crocus a few weeks later as they can easily skip ahead. Snowdrops are intricate and can be expensive so are often enjoyed more in pots. It is essential to protect against mice and squirrels. Upturned, aquatic mesh pots and mouse traps work well. Watering is crucial, roots must not dry out once the plant is in growth. They require consistent moisture but avoid wet conditions.

Suitable bulbs for forcing

All the plants and bulbs below have been used in the displays above.

Iris reticulata 'Katharine Hodgkin', Crocus chrysanthus 'Romance', Muscari armeniacum and Anemone blanda 'Charmer'
Clockwise from left: Crocus chrysanthus 'Romance' Iris reticulata 'Katharine Hodgkin', Anemone blanda 'Charmer', Muscari armeniacum

Muscari macrocarpum ‘Golden Fragrance’
These choice bulbs are unusual and worth seeking out. The highly fragrant, greenish flowers turn a rich yellow with age. 18cm.

Iris ‘Katharine Hodgkin’ (Reticulata)
My queen of the dwarf iris. Bred in the 1960s by enthusiast EB Anderson, this pale-blue iris is long lived and even after forcing it is worth planting outside amid snowdrops and cyclamen. The flowers are wide and opulent, with sea-green veining and soft, yellow-blue tones. 12cm. AGM.

Scilla messeniaca
Lesser-known but more impressive than Scilla siberica. It has up to seven leaves and an abundance of flowers on each stem. 15cm.

Crocus ‘Romance’
Very free flowering bulb, and an usual primrose yellow. Will establish easily if planted out. 7-10cm.

Muscari aucheri
One of the loveliest blues, and strongly scented. Works well in a pot indoors so that the scent can perfume a room. 12cm.

Anemone blanda ‘Charmer'
Pretty, pale-pink flowers with a light centre. The divided foliage has pinky tones on the underside of the leaf. 12-15cm.

Crocus ‘Ruby Giant’
With purple hues that are much richer than others in this group and wonderful contrasting golden anthers, this is a showy and fragrant early cultivar. 12cm.

Galanthus nivalis ‘Viridapice’
Single drooping flowers with a distinctive green blotch at the tips. No need to ‘force’ as it flowers early, but bring into the warm to get them flowering. 15cm.


Cyclamen coum f. pallidum ‘Album’
Spring-flowering cyclamen, from the pine and beech woodland of southeastern Europe and the Middle East. Flowers range from dark magenta to the white form I have used here. 8-12cm.


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