Many Types of Bulbs are grown indoors and greenhouses to filter out the winter. The majority are started around Christmas time. Bulbs require a special type of compost known as Bulb Fibre.
You can either purchase this in bags of various sizes, or if you are so inclined, you can easily make your own bulb fibre. You should not use ordinary potting compost for this purpose.
Ordinary potting compost will have fertilizer added, and the generally moist conditions required for growing bulbs indoors will render the compost unsuitable for this use.
Reason being, that bulbs being grown indoors are normally grown in a pot or bowl with no drainage holes. This makes for a tidy display, with no water dripping through on to a prized item of furniture.
As the bulb being forced, does not require or use the fertilizer present in normal potting compost, the moist growing conditions will keep releasing chemicals from the fertilizer into the bulb compost, where they will be turned into mineral salts that are eventually detrimental to the bulb's wellbeing.
Bowl of Indoor Bulbs
Firstly - and important for the reasons mentioned above - there are no feeds or fertilizers added to bulb fibre. Indoor Bulbs - or those that are grown for flowering indoors - do not need fertiliser for growth.
The basis of the Bulb Fibre Compost, is either normal Sphagnum Moss Peat or Coir by way of coconut husks ground to fibre. Do NOT use Coir Potting compost for this. I normally like to add around 25% by volume of horticultural Vermiculite or Perlite to the peat base. This opens up the Bulb Fibre compost a little to allow air into the depth of the bulb fibre. Especially important, because of the moist conditions of the bulb fibre at all times.
Charcoal - The main addition that will be required to the bulb compost, will be a small handful of ground charcoal per 8in bowl size of compost. Leftover BBQ charcoal, crushed down - not into dust though - will be suitable for this. The charcoal has the effect of keeping the bulb fibre 'sweet' and not rancid as may otherwise be the case. wet peat is basically acid, and if not allowed to dry out a little, will become putrid and stagnate. The smell will be unpleasant, and rotting of the bulbs can take place.
Oyster Shell - If you live near the seaside, then you can collect a few dozen old sea shells - oysters were the norm - and crush them - adding them to the bulb fibre. Do make sure you thoroughly wash the shell material before crushing and adding. A bowl of beautiful hyacinth bulbs near the Christmas dinner might look gorgeous, but the scent of the Hyacinths should take precedence over the smell of rotting cockle fragments!
If you make too much bulb fibre, then it can be turned into useful potting compost for the late winter early spring, by the addition of osmocote fertilizer.