Rhubarb (genus Rheum)
(Heavily from https://bonnieplants.com/blogs/how-to-grow/growing-rhubarb.)
What grows for 10 years or more, suffers from almost no pests, and is refreshingly easy to care for? It’s rhubarb! This perennial vegetable has tart-flavored ruby or green stems used to make pies, crumbles, cakes, jams, and sauces.
Rhubarb thrives in areas with a cooler climate, making it popular in northern gardens. Rhubarb is easy to grow but needs a dormancy period to thrive and produce an abundance of huge stalks. It does best where the average temperature falls below 40ºF (4°C) in the winter and below 75ºF (24°C) in the summer.
The stalks are the only edible part of the rhubarb plant. These have a rich, tart flavor when cooked. The leaves of the rhubarb plant are toxic. They contain an irritant called oxalic acid, so be sure that they are not ingested.
Description
Rheum species are herbaceous perennials growing from fleshy roots. They have upright growing stems and mostly basal, deciduous leaves growing from short, thick rhizomes. They have persistent or deciduous ocrea. The inflorescences are terminal and panicle-like with pedicels. The hermaphrodite flowers consist of a whitish green to pinkish green, hairless and campanulate (bell-shaped) perianth, composed of six tepals. The outer three tepals are narrower than the inner three and all are sepal-like in appearance. The flowers have nine (sometimes six) stamina inserted on the torus at the base of the peranthium, they are free or subconnate at their base. The anthers are yellow or pinkish green, elliptic in shape. The ovary is simple and triangular shaped with three erect or deflexed styles. The stigmas are head-like. The fruits are a three-sided achene with winged sides, and the seeds are albuminous with a straight or curved embryo.
Cultivation
A true perennial, rhubarb plants can yield harvests 5 to 8 years or longer. Once plants are established, they don't transplant easily, so choose your planting site carefully.
Rhubarb grows best in zones where the ground freezes in winter. Plants require an extended chilling period to produce a crop of stems.
Established plants need to be divided every 5 to 10 years. You'll know it's time to divide when stems are crowded and thin. Divide when plants are dormant, in early spring or fall. Dig and lift clumps, cutting roots into pieces about 2 inches across. Take care not to damage the buds on the top of each root section. Replant the best sections.
Pests
Few problems plague rhubarb. Crown rot settles in when soil drainage is poor. This disease damages terminal buds, which results in spindly, weak stems. The cure is to dig out and burn infected plants. Don't replant rhubarb in areas where crown rot has damaged plants before.
Leaf spots can attack the plant, with the worst being red leaf, or Ramularia, which can ruin the stems. Cut away old foliage in fall to help prevent leaf spot, whose spores overwinter in the debris.
Rhubarb curculio occasionally attacks plants. Insects puncture leaf stalks from late spring to early summer as they feed and lay eggs. Damaged stems ooze sap and may begin to decay.
Harvesting
Forget harvesting the year that you add rhubarb to the garden. In the second year after planting, harvest lightly, removing only a few stalks from each plant. From the third year on, harvest stems freely. To ensure continued production, take care not to remove more than one-third to one-half the stalks from any one plant during any one harvest.
To harvest, choose stems that are 12 to 18 inches long and reddish in color. Grasp the stalk near the base and pull it upwards, twisting the stem as you pull. You can also use a sharp knife to slice stems from the plant. Cut as close to the crown as possible without damaging it. After harvesting, remove the leafy portion and the base of the stem, leaving only the colored stalk.
Early spring stems offer the most flavor and tenderness; they're ideal for pies. Stems harvested later in the season tend to be tougher, so reserve them for stewing, sauces, or jams.
Stop harvesting as stems get shorter and thinner. At this point, plants are storing up energy for next year's harvest. Mature plants typically provide an 8- to 10-week harvest. In general, expect about two kilograms (2 to 3 pounds) of stalks per mature plant per season.