Hyacinths don’t normally flower at Christmas, but with some cheating they can be made to if planted in September. Your greenhouse can protect growing plants and their emerging flowers from frost, wind and rain, and give enough heat to speed up their flowering.
Hyacinths won’t flower for Christmas unless they are given a heat treatment. These ‘prepared’ bulbs are what to buy. After use they can be planted in the garden to flower normally in later years, but won’t flower early again without another heat treatment.
To avoid staining indoor furniture, use a pot or container that has a suitable saucer or is non-porous and without drainage holes. Use potting compost, or the coarser bulb fibre if the container has no drainage holes. Put a layer of moistened compost or fibre in the bottom of the container and stand the bulbs upright on it, not quite touching each other or the sides. Plants look better in threes or fives than in even numbers. Top up with more fibre or compost to about finger width below the container edge: the tops of the bulbs should be exposed.
Keep them moist in a cold, dark, frost-free place (such as in a black plastic bag in a cellar) for a few weeks until the shoots are about four centimetres high, and then move them to a shady spot in the greenhouse to green up for a week. Aim to have the plants at this stage by the start of December. Move them to a sunny spot in the house until the flower buds appear, and then to their flowering position. Hyacinths can be pushed on a bit faster in the warmth of the greenhouse, but only in these last stages. Keep them moist but not wet and feed them occasionally.