Room 10, of Balclutha Primary School, asks :-
We have a new rhubarb plant in the science garden. Is it true that rhubarb should not be harvested for the first 3 to 4 years? Is this why the stalks on the rhubarb are green and not red?
Roy Edwards, a horticultural botanist at Lincoln University, responded.
Rhubarb plants are native to parts of China and die down to a crown in the winter. New growth starts after temperatures rise and day length increases in spring. In autumn the leaves of rhubarb die and provide a surface mulch which helps protect the roots from cold. Rhubarb grows well in a warm sunny site with deep well drained soils containing organic matter and responds to water in the summer.
To pick rhubarb each year you need to look after the plants by only taking some of the leaves every time you harvest. You may get two or three pickings over the season. In the first and second harvest pick, take only the largest stems, possibly 70-80% of all leaves. The last harvest should be done leaving about 50% (the smallest leaves) when you can expect about another month of growth to still occur.
The leaves left on the plant die down and supply the below ground parts with carbohydrate to power new growth the following spring. If no leaves are left plants get weaker and less productive.
For the same reasons, when you plant a new rhubarb plant, it is a good idea to not pick any leaves in the first season. This allows the plant to establish and develop a good healthy root system producing rhubarb leaves and stalks that can be harvested from the second year on.
Garden rhubarb (Rheum Xcultorum) is a hybrid from which a number of cultivars have been selected, some have red leaf stalks and others green. If you prefer red stemmed rhubarb, you need to obtain a red stemmed plant. This can then be divided in the winter and you can replant both portions to increase the number of red stalked plants you have. The same applies to green stalked rhubarb.