Rhubarb

May 05, 2010

by Helen Halpenny Lanark County Master Gardeners

Rhubarb, ‘Rheum rhubarbarbum’, the staple of every garden, is the first spring crop we pick for pies and jam. But some varieties of ‘Rheum’ are also striking ornamental plants. With large umbrella-like leaves that contrast with red stems. Rhubarb is a handsome plant and it grows well in our cold Canadian climate. All rhubarbs are high in Vitamin C. It used to be used in olden times for medicinal purposes. By the eighteenth century, it became food. Although we think of it as a fruit, we eat the petiole, or leaf stem. Rhubarb leaves are poisonous. Both leaves and root contain high amounts of oxalic acid that can cause the throat and tongue to swell and prevent breathing.

The plant grows from rhizomes that will live for many years. It sends up sprays of creamy-coloured flowers that are quite ornamental but if you are growing your plant for food, it is best to remove the flower stalks so more edible stalks will grow. Rhubarb stalks are pulled from the roots, not cut off. And harvesting from a well-grown plant can be done from early in May until mid-summer. Then the plant needs to store food in its roots for the winter. Water plants well before freeze up.

Rhubarb likes well-drained, good soil that is slightly acidic, but it will grow in clay. The addition of compost or well-rotted manure each spring is beneficial. Plant rhubarb as you would peonies - with the tops of the rhizomes just below the surface of the soil. Incorporate lots of compost at planting time and your rhubarb plants will produce abundant crops in their second year after being established. A slightly raised bed will ensure good drainage and prevent crown rot. If you want more rhubarb plants, then first thing in the spring dig up and split the plant. Separate the mature root with a sharp knife and replant the sections. Keep the transplants moist while they settle in.

Yes, you can compost rhubarb leaves. The oxalic acid contained in the leaves breaks down during the composting process.

Ornamental rhubarbs are highly decorative with their deeply cut leaves and tall branching flower spikes. They are good plants for wild areas and pond-side groupings. Rheum palmatum, native to China, is a huge plant with leaves up to 100cm across and white flowers, usually. ‘Atropurpureum’ has young crimson-purple leaves and pink flowers. All ornamental rheums require very rich, moist soil, well-manured each year, to grow to their full potential.

For more gardening information, call Renai Rennick at 613-267-7272.