Rhubarb is a vegetable that is commonly used to make pies, jams, and other sweet treats. The edible part of rhubarb is the stalk, which can range in color from red to green. While the tart, red stalks are used in most rhubarb recipes, some people enjoy eating the green stalks raw or cooked as well. However, there is some debate over whether or not green rhubarb stalks are safe to eat.
What causes rhubarb stalks to be green?
Rhubarb stalks start out green when they first emerge from the ground. As they grow, sunlight causes them to produce red pigments called anthocyanins, turning the stalks a red color. The amount of red pigment depends on the rhubarb variety, weather conditions, and sunlight exposure. Stalks that are covered or in the shade will remain greener than exposed stalks.
Some reasons rhubarb stalks may stay green include:
Immature plants
On young rhubarb plants that are one to two years old, the stalks may not have had time to accumulate enough red pigment. The stalks will be milder tasting and all green.
Low light conditions
Rhubarb grown in shade or with coverings may be pale green rather than red. Less sunlight means less anthocyanin production.
Overharvesting
Overharvesting rhubarb stalks without allowing the plant to re-grow can prevent full red color development.
Cool weather
Extended cool and cloudy weather can inhibit anthocyanin synthesis, causing greener stalks.
Specific varieties
Some rhubarb varieties, like Victoria and Valentine, turn greener rather than red even when mature and exposed to sunlight.
So in summary, green color in rhubarb stalks is usually just an indication of maturity, light conditions, or variety – not safety.
Are green rhubarb stalks poisonous?
Some sources claim that green rhubarb stalks contain high levels of oxalic acid, making them toxic. However, there’s no evidence that oxalic acid content differs between green and red stalks.
All rhubarb contains oxalic acid, giving it a tart taste. But both green and red stalks contain similar, safe levels in the edible stalks when harvested at the right stage of maturity. The leaves, however, contain dangerously high and potentially toxic levels of oxalic acid and should never be eaten.
So while the leaves are poisonous, green stalks themselves are not toxic or unsafe to eat.
Oxalic acid content
Typical oxalic acid levels in rhubarb stalks:
- Green stalks: 200-600 mg per 100g
- Red stalks: 200-600 mg per 100g
For comparison:
- Spinach: 750 mg per 100g
- Chard: 200-350 mg per 100g
As you can see, rhubarb stalks are in the same range as many other common vegetables. The oxalic acid level does not appear to be higher in green stalks.
Calcium binding
Oxalic acid can bind to calcium in the body, preventing absorption. But you would have to eat very large quantities of rhubarb stalks, green or red, to negatively impact calcium levels.
Taste and texture differences
While not toxic, green rhubarb stalks do differ from red ones in taste and texture:
Taste
Green rhubarb stalks tend to be more bitter and astringent than red stalks. They lack the sweetness from higher levels of glucose that accumulate in red stalks. The bitterness is due to higher levels of structural and metabolic phenolic compounds.
Texture
Green rhubarb stalks tend to be tougher and more fibrous than red ones. As they age, stalks become softer and more succulent.
Cooking differences
Due to the texture and taste differences, green rhubarb requires longer cooking times and more added sugar to make it palatable in recipes. It works better in dishes where it can be mixed with sweeter ingredients.
When is green rhubarb safe to harvest?
Here are some guidelines for determining if green rhubarb stalks are mature enough to harvest safely:
Plant age
Only harvest rhubarb from plants that are at least 2-3 years old. The oxalic acid content of young plants may still be too high.
Stalk width
Mature rhubarb stalks should be at least 1 inch (2.5 cm) thick at the base. Older, well-established plants may have thicker stalks up to 2 inches (5 cm).
Leaf development
Don’t harvest any stalks until the leaves have fully developed and uncurled. This is a sign the plant has reached maturity.
Harvest season
Only harvest during the normal season for your region. In most temperate climates, this is typically from early spring to early summer.
Weather conditions
Cool, cloudy weather can delay maturity and color development. During spells of persistently overcast weather, wait to harvest until conditions improve and plants have time to mature properly.
As long as the plant is mature and stalks are harvested from healthy, undamaged plants at the right stage of growth, green rhubarb stalks are not toxic and can be eaten. Damaged or diseased plants should be avoided.
Cooking and eating green rhubarb stalks
Here are some tips for preparing green rhubarb stalks:
Peel the stalks
The outermost part of the stalk will be stringiest. Peel the stalks with a vegetable peeler.
Cook thoroughly
Green rhubarb needs to be cooked longer than red to soften it and bring out the flavor. Bake, roast or stew for at least 15 minutes.
Add extra sugar
Due to the bitter taste, green rhubarb requires more sweetener. Add sugar, honey, fruit juice or puree to balance the bitterness.
Pair with sweeter ingredients
Combine green rhubarb with ingredients like strawberries, stone fruits, citrus juice, ginger, or applesauce.
Use in savory dishes
The tart, bitter notes of green rhubarb work well in savory dishes like chutneys, sauces, and glazes.
Bake into desserts
Baked goods can mask bitterness. Try green stalks in pies, tarts, crumbles, and cakes.
Ferment into wine or soda
Fermentation can mellow bitterness. Brew green rhubarb into wine, kombucha, soda, cider, or vinegar.
Nutrition of green vs. red rhubarb
Green and red rhubarb have very similar nutritional profiles. Both are low calorie, high fiber vegetables that provide vitamin C, vitamin K, calcium, manganese and antioxidants.
However, red rhubarb stalks contain higher levels of beneficial plant pigments, including:
Anthocyanins
Red pigments with antioxidant and anti-inflammatory effects.
Beta-carotene
An orange pigment and precursor to vitamin A. Important for immune function and vision.
So while green rhubarb isn’t toxic, red stalks will provide more nutritional value.
Can you freeze green rhubarb stalks?
Yes, green rhubarb can be frozen for later use:
Wash and trim ends
Rinse stalks and trim any dry ends before freezing.
Cut into pieces
Cut stalks into 1-2 inch pieces for easier use when thawed.
Blanch briefly
For better texture, blanch pieces for 1 minute then shock in ice water before freezing.
Pack in air-tight containers
Place pieces in freezer bags or plastic containers, removing as much air as possible.
Freeze
Store frozen rhubarb at 0°F (-18°C) or below for up to one year.
Use frozen
Frozen green rhubarb can be used in all the same recipes as fresh. Thaw before using.
Freezing can help tenderize green rhubarb stalks, as ice crystals break down tough fibers.
Can you juice green rhubarb stalks?
Green rhubarb can be juiced, but produces a bitter, tart juice. It is often combined with sweeter fruits and vegetables when juicing.
Some ways to use green rhubarb juice:
Juice with apples, carrots, beets or citrus
Mix with sweet fruits and veggies to offset bitterness
Dilute with water or ice
Add water to dilute and reduce sourness
Blend into smoothies
Combine with bananas, berries, spinach, or kale
Sweeten with honey, sugar, stevia
Add sweetener to taste to balance tartness
Use in cocktail mixes
Splash into gin, vodka, or sparkling wine cocktails
Bake into snacks or desserts
Use as a natural sweetener in energy bites, popsicles, or baked goods
Conclusion
Green rhubarb stalks are not toxic or unsafe to eat, despite their bitter taste and fibrous texture. While not as tasty or nutritious as red stalks, green rhubarb can still be enjoyed as long as the plant is mature and healthy. With proper harvesting, preparation, and added sweetness, green rhubarb stalks can be a tart, versatile ingredient. Just be sure to remove and discard the leaves, which do contain high oxalic acid levels. When in doubt about safety, stick to harvesting only firm, red rhubarb stalks.
