Plant lilies in pots
Lily bulbs can be planted in pots, for flowers this summer. After growing on in a cool greenhouse, they can be moved on to the patio when in flower.
Rhubarb can be forced for an early crop. Cover a crown or two with buckets or even an upturned large pot and insulate the outside with straw or compost for added heat. The stalks will grow in the dark. This takes a lot out of the crown and it won’t recover for a couple of years.
Make sure tender perennials are OK
Check on tender plants overwintering outdoors to make sure protective coverings are still in place.
Create a new pond
You could dig a new pond. Have a minimum depth of 60cm (2ft) at the deepest point, to reduce the risk of the pond freezing totally. Gently sloping contours between the shallow and deep areas, and between the bank and the water, are more wildlife-friendly.
Let there be light!
If you do have any seedlings and/or cuttings in the greenhouse, make sure they are getting the maximum light available, or else they will become weak and leggy. If necessary, turn them once a day so that they get light on both sides. This will stop them leaning over towards the light, and keep them upright and compact.