The most significant factor deciding whether a rhubarb stalk is red or green is the plant’s genetic makeup, specifically the cultivar or variety. The red hue comes from pigments called anthocyanins, which are natural compounds also responsible for the color in blueberries and red cabbage. Varieties like ‘Valentine’ and ‘Canada Red’ are genetically predisposed to produce elevated levels of these pigments, resulting in deeply colored stalks.

However, many perfectly healthy and popular varieties, such as ‘Victoria’ or ‘Green Stalk,’ are simply bred to produce extraordinarily little or no anthocyanin. These plants will be green regardless of how long they are left in the ground or how they are grown. The absence of this pigment is a stable genetic trait, not a flaw. Therefore, a bright green stalk is not an unripe stalk; it is simply a genetically green stalk.

A primary concern for many growers is whether a green stalk is safe to consume, and the answer is an unambiguous yes. The color of the stalk offers no sign of the concentration of oxalic acid, which is the compound that makes rhubarb leaves toxic.

Rhubarb leaves have elevated levels of oxalic acid and should always be removed and discarded before cooking. The edible green stalks are just as safe as red ones and have a negligible amount of the compound. The main difference between the colors is a slight variation in flavor profile. Green varieties are often described as having a more intensely tart flavor than their red counterparts, which may require slightly more sugar in recipes. The texture and cooking performance are essentially identical, and some green varieties are prized for their superior yield and less stringy texture.

Bolting occurs when the plant sends up a tall flower stalk. This is a normal part of the life cycle, especially in older plants or during heat stress.

The best method is to remove the flower stalk as soon as it appears. The flower stalk can be composted or discarded. This redirects energy back into the roots and edible stalks. The green stalks with leaves can be used in your favorite recipe. Continue to remove new flower stalks if they appear. Divide the rhubarb every four to five years to reduce bolting tendency. Avoid plant heat stress, drought, and poor nutrition which can increase bolting.

Further guidance can be found in this article from Purdue University Extension, the is found here: Rhubarb is prone to bolting. Here’s what to do - Indiana Yard and Garden - Purdue Consumer HorticulturePurdue University Indiana Yard and Garden – Purdue Consumer Horticulture Another article from Oregon State University Extension offers growing advice and a recipe for Strawberry. Rhubarb Upside Down Cake: Grow your own rhubarb | OSU Extension Service

Thank you for your question and have a great gardening season.