Rhubarb’s tart stalks are a welcome sign of spring. Many gardeners and shoppers seek deep red stalks, believing the color indicates a sweeter or better-tasting product. The appearance of green rhubarb often leads to the question of whether it can be ripened, similar to fruits left on a counter. Rhubarb stalks are safe to eat regardless of color, provided the toxic leaves are removed before preparation.
Understanding Rhubarb Coloration
The color of a rhubarb stalk is primarily determined by two factors: the plant’s genetic makeup and its growing conditions. Some rhubarb varieties, such as ‘Victoria’ and ‘Riverside Giant,’ are naturally green-stalked, even when fully mature. These varieties will never develop a deep red hue because they lack the genetic coding for high anthocyanin production, the pigment responsible for red coloring.
Environmental factors also play a significant role in pigment development, particularly for genetically red varieties. The stalks require ample sunlight, ideally at least six hours of direct sun daily, to synthesize the necessary anthocyanin compounds. A lack of sufficient light, or growth in overly rich soil with excess nitrogen, can result in a paler, greener stalk, even on a plant meant to be red.
Debunking Post-Harvest “Ripening”
The simple answer to whether you can ripen green rhubarb after it has been picked is no; the stalk color will not change. Rhubarb is a vegetable grown for its leaf stalks, or petioles, not a climacteric fruit that continues to ripen after being harvested. Once the stalk is severed from the plant, the biological processes that produce color pigments, such as anthocyanins, essentially stop.
Leaving a harvested green stalk on a counter or in a bag will not turn it red. Any minor color change you might observe would be due to moisture loss, which can slightly concentrate the existing pigments, but it is not true ripening. Rhubarb is best used shortly after harvest, as the stalks can quickly dry out and become stringy over time.
Techniques for Enhancing Stalk Color
Gardeners who desire redder stalks must focus on manipulating the plant’s growth conditions while it is still in the ground. Ensuring the rhubarb receives full sunlight is the most direct way to encourage anthocyanin production in genetically red varieties. Plants in shadier spots will consistently yield lighter, greener stalks.
Forcing
A technique known as “forcing” can also be used to produce pale pink stalks early in the season. Forcing involves covering the rhubarb crowns with a dark container, like a terracotta forcer or an overturned bucket, to exclude all light. This causes the plant to grow rapidly in search of light, producing long, tender, and less tart stalks that are typically a delicate pink rather than a deep red. This method also reduces the concentration of oxalic acid within the stalks, resulting in a sweeter, milder flavor.
Soil health also influences stalk color. Rhubarb prefers slightly acidic soil. Maintaining balanced soil nutrition and avoiding excessive nitrogen can help promote better pigmentation. Proper harvesting, by pulling and twisting the stalk from the crown, promotes overall plant vigor.
Preparing and Using Green Rhubarb
Since green rhubarb cannot be ripened, the best course of action is to use it as is. Green-stalked varieties often have a more intensely tart flavor compared to their red counterparts, which is a desirable trait for many culinary applications. The tartness is due to organic acids.
When using green rhubarb in recipes, you may need to adjust the amount of sugar to balance the increased acidity. Adding an extra tablespoon of sugar per pound is a common starting point, or you can blend it with sweeter ingredients like strawberries or raspberries. The cooked product will be a pale green or greenish-brown color, offering a pure, bright flavor.