Rhubarb is a relatively easy plant to grow and when given the right growing conditions can continue to provide you with delicious stalks for pies and puddings year after year. Rhubarb needs a sunny site with moist but free-draining soil. It will not do well where the roots can become waterlogged in winter and so a polytunnel, where the water can be more controlled, can be a good environment for it to grow well.
It is important that rhubarb is subjected to a period of winter cold, but an unheated polytunnel will still allow this to happen, yet will protect the crowns from hard frosts and the worst of the winter weather. If planted inadvertently in a frost pocket, rhubarb stems can be damaged.
Rhubarb can be grown from seed but it is more common for it to be planted as dormant crowns between autumn and spring. Now could be a good time to purchase a crown or two and plant them in your polytunnel. Make sure you leave enough space for each plant and remember to consider where you plant them carefully, as rhubarb will remain in the same location year after year.
It is also important to make sure that you have prepared your planting area well. Rhubarb should be planted in an area which has been prepared by adding a good quantity of well-rotted manure or compost. These are hungry plants and so it is essential to make sure you have provided a rich growing medium well able to cater to its needs as it grows. As it does so, remember also that it will need to be well-watered to keep soil moist throughout the year.
If you do not have any bed space in your polytunnel for rhubarb, you can also consider growing it in a container – though the container will have to be at least 50cm across and 50cm deep to accommodate the rhubarb plant effectively.
To plant the rhubarb crown, spread out the roots and plant so that the tip of the crown is just visible above the ground. Plants should ideally be spaced around 75cm apart. This will ensure that each plant has the space and nutrients it needs to grow without compromising the growth of its neighbours.
It is not a good idea to harvest rhubarb the first year after planting. Leaving it to grow will give it time to establish itself properly. Thereafter, you can remove a few stems each year, up until June. Pull off the stems carefully and leave some to keep each plant in active growth.