Rhubarb: flowers, toxicity & nutrients


With a passion for growing installed at an early age, I have always been happiest outdoors in nature. After training as a professional gardener and horticultural therapist, I currently run horticultural therapy and community kitchen gardens in the UK, helping others access the many physical and mental health benefits of growing vegetables, fruit and plants.

Favourite fruit: apples and pears
Favourite vegetable: asparagus

With its flavoursome stalks, rhubarb is widely grown in allotments and gardens. Discover more about rhubarb and which parts are edible.

Rhubarb growing in the ground
Rhubarb plants can remain productive for up to 10 years [Photo: daseaford/ Shutterstock.com]

As a hardy perennial, Rhubarb (Rheum x hybridum) dies back in the winter before producing new stems the following spring. Normally used for making desserts, we will show you some other rhubarb uses and discuss its toxicity.

Rhubarb: origin and characteristics

With its origins in parts of Asia, rhubarb has been cultivated for several thousand years. However, it was not introduced to the United Kingdom until the 18th century, after which commercial cultivation began. As a member of the Polygonaceae family, also known as the knotweed family, rhubarb is tough and well suited to our temperate climate.

Rhubarb requires space to grow because it grows vigorously and can reach heights and widths of more than 1m. Depending on the rhubarb variety, it develops green, pink or red stems upon which its large heart-shaped leaves grow. During the summer months, rhubarb flowers can sometimes develop on thick stalks. To divert the energy back into the plant, you can remove any flowering rhubarb stems as soon as they appear.

Is rhubarb a fruit or vegetable?

If you are wondering whether rhubarb is a fruit or a vegetable, it is technically classified as a vegetable. However, its stems are most commonly eaten like a fruit in desserts such as crumbles and pies. Although rhubarb and celery (Apium graveolens var. dulce) resemble each other somewhat, they are not related.

Rhubarb plant producing a flower
If rhubarb flowers develop, you can remove them to divert the energy back into the plant [Photo: ValdisOsins/ Shutterstock.com]

Is rhubarb poisonous?

The only parts of rhubarb that are edible are the stems or stalks, which you can eat either raw or cooked. However, be prepared if you try them raw, as they can be extremely tart. Rhubarb leaves are poisonous both to humans and animals because they contain high levels of oxalic acid, which is a nephrotoxin. Care should also be taken not to eat excessive amounts of rhubarb stems, especially later in the season due to their higher oxalic acid levels, as large amounts of oxalic acid can lead to hyperoxaluria and kidney stone formation. However, another reason for not harvesting rhubarb beyond mid-summer is that it can weaken the plant and lead to a poor crop the following year. It is interesting to note that raw rhubarb stems contain the most oxalic acid, but you can lower the levels by peeling and cooking the stems. Due to the levels of oxalic acid in rhubarb, consumption is generally inadvisable for those who are pregnant, breastfeeding or for toddlers.

Rhubarb leaf surrounded by snow
Rhubarb is tough and winter hardy [Photo: JGade/ Shutterstock.com]


Rhubarb is winter hardy and is rated H5, which indicates that when mature it can withstand temperatures down to -10 to -15 °C and sometimes even lower. As the leaves die back in the autumn, you can remove them by hand or cut them off if necessary, being careful not to damage the crowns. With container-grown specimens, you can overwinter rhubarb in a sheltered location. However, it is best to not bring them undercover as rhubarb actually requires around 2 months of temperatures close to 0 °C to produce a good harvest in the spring. If extremely low temperatures are forecast or if you have any young plants, you can cover your rhubarb crowns with a layer of fleece or straw to protect the rhubarb crowns from being damaged.

Nutrients and uses

Rhubarb is nutrient-rich, low in calories and a great source of antioxidants and vitamins, especially C and K. Rhubarb tastes slightly sour, and perhaps the most common way of eating rhubarb is when it is combined with sugar to make puddings such as crumbles and pies. However, these are not the only ways, as you can use rhubarb to make jam, tarts and even wine. Furthermore, rhubarb roots have long been used in traditional Chinese medicine for antibacterial and anti-inflammatory purposes.

Rhubarb stems prepared for cooking
Rhubarb can be used in crumbles, jams, pies and even for making wine [Photo: Anna Shepulova/ Shutterstock.com]

You can keep rhubarb in the fridge for around 10 to 14 days. However, for larger harvests, learn how to store rhubarb to make it last longer.