My rhubarb is stunted even though I have been fertilising it. Why is this?
Rhubarb is a favourite plant in home gardens with the right hardiness zone and soil type and fertility. Rheum rharbarum is a hardy perennial in the Polygonacea family native to Asia. Its stalks are delicious although tart. The leaves are toxic to humans and animals. Rhubarb grows best in an open sunny site with moist but free draining soil that is slightly acid. Soils that get waterlogged contribute to rotting plants as not enough oxygen is in the soil. Consistent moisture is important to maintaining plant health so regular watering is required. Rhubarb can be grown in raised beds giving the soil ability to drain in wet weather.
The crop requires winter temperatures below 4C to break dormancy and summer temperatures less than 24C. As rhubarb is a very hardy plant to -30C it will survive our recent cold snaps. We have had summer temperatures much higher than 24C on occasion so the ability of the plant to survive in hot temperatures is compromised. A small amount of shade in mid to late afternoon for a short time if it can be grown there but still have 6 hours of sun is ideal in these hotter summers. The tops freeze in the first heavy frost but the roots survive if the soil is not waterlogged. Fertile, loamy, well drained soil that has good organic matter (well rotted compost) is required and at least 6 hours of sun during the growing season.
Rhubarb is a perennial harvested before summer. Place young crowns in a south facing exposure giving plenty of room from nearby plants. In early spring plant crowns as soon as they are available in nurseries or by mail order. Don’t use any chemical fertilizer on a young plant as the nitrates can kill it. As the plant grows add organic matter in the spring (don’t dig it in as the action can disturb the roots) and when active growth occurs. Don’t work fertilizer into soil for established plants but apply organic compost as a mulch. Crowns should be spaced 30” apart and no more than an inch or two of soil on top and the depth of soil loosened to 10”. When the plants are growing but young add a well rotted organic mulch of 3-4 inches to maintain soil moisture and help keep the roots cool. Remove flower stalks as they appear. Keep the soil moist with irrigation but not soggy.
Remove any leaf litter from the previous season to avoid disease potential. Only harvest leafstalks lightly the second year and none at all in the first year. When the plant sends up slender stalks later in the growing season it is time to stop harvesting to preserve enough foliage to preserve the crown. Harvest stalks when colourfully pink and young for best flavour. In fall the tops of the plant may be frost killed. At this point add 2-3” of straw as mulch over top of the plant. In spring, move the mulch from the plant top to surround the plant’s roots. Leaves can be safely composted.
Plants can be divided by digging them up at 6-10 years old. Do this very early in the spring when the soil can be worked. Lift the plant and break off buds with one bud and a large root piece. Small pieces that break off can be grouped together but will take more time to establish. Replant the crown divisions right away. Prior to planting add organic fertilizer and compost into the planting soil and compost again on soil surface. Mulch with straw.
Sources
https://ohioline.osu.edu/factsheet/hyg-1631
https://www.thespruce.com/growing-rhubarb-1403450
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