Owning a greenhouse, even a plastic pop up one, is a great help to gently forcing spring flowering bulbs.
Forcing means to cause plants to come into growth earlier than they normally would. In the case of bulbs, this means you can have pots of flowers around the house as early as Christmas – weeks before they are in bloom outside.
So, instead of planting bulbs such as daffodils and tulips in the ground or in a pot which you then leave outside, keep the pot in your greenhouse and automatically your bulbs will come into life sooner. With no wind and warmer temperatures, especially around the roots, it makes a terrific difference.
When growing bulbs in containers, drainage is important so have plenty of crocks (broken flower pots, scalpings or stones in the bottom of your pot.
If you’re not using a specialist bulb mixture, make your own using a compost like John Innes No 2. This includes some horticultural grit in a ratio of 2 parts compost and 1 part grit.
The compost should be damp but never saturated and should remain moist while the bulb is itself rooting.
With bulbs, roots happen well before leaf, but be patient and you’ll eventually see some top growth. When that happens, position the pots so that they get maximum light in the greenhouse and turn them every few days so they don’t head off in the wrong direction.
Make space on the window sill
Just before they are about to flower you can then bring them into the house to be placed on a sunny window sill, the same space where your window boxes are is fine. This will accelerate the rate of development – they will rush into flower and fill the house with the scent of spring. In winter.
If you want to be a bit more radical and produce, for example, hyacinths at Christmas or paperwhites in January you need to ‘prepare’ the bulbs.
This means that you need to create the sort of conditions that bulbs would normally experience in winter, before winter comes, so that you ‘fool’ them into flowering early.
The easiest way to do this is to buy them ready prepared, but they are more expensive like this and it is not hard to do it yourself. Just be aware of the most prevalent gardening mistakes and you will be all right.
Find a cold dark place
Potting needs to be done early.
The potted bulbs need to be kept somewhere cold (ideally between 4 and 6 degrees centigrade) and completely dark for between 10 and 16 weeks. The larger the bulb, the longer the chilling required.
I find the best place to do this is in an unheated lean-to that faces north against the back wall of my garage. It never sees the sun and is dark and chilly. But if you’re just doing a couple of pots, you can put them in the drinks fridge…
Absence of light is important with all bulbs except paperwhites and you can achieve this by covering the pots with a cardboard box.
It’s fine for the temperature to rise above that ideal range occasionally, but consistently warmer temperatures will cause the flower buds to form in the bulb (rather than on the end of the stalk).
Keep an eye on the roots
You’ll know that the bulbs are ready for the next stage when you can see roots emerging through the drainage holes at the bottom of the pot. Or you may even see obvious top growth (about 5-10 cm for hyacinths).
You can get scientific with this, or do it my favourite way and try to wiggle the bulbs – they should feel well secured.
Get this stage right and the next bit is easy.
Once you’re sure that the bulbs are well rooted, move them to a bright, light spot that’s a bit warmer – about 15 degrees centigrade – so that the bulbs start to grow more rapidly but they have a chance to get used to the increased warmth and light.
They need to stay here for 2-3 weeks otherwise the stalks become weak and elongated and your flowers will flop over.
After this warming up period, move them to a sunny, south facing window sill for the final flowering. Turn the pot by a quarter turn every day so that they grow straight. Your prize flowers will last longer if you then take them out of direct sunlight when they’ve opened and display them somewhere slightly cooler.
Julien de Bosdari is an avid gardener and the Owner of Ashridge Trees, founded in 1949 and still going to this day they supply hand picked top quality plants from hedging to flower bulbs to fruit trees among many others.