Can You Use Rhubarb Leaves for Compost?

Can You Use Rhubarb Leaves for Compost

Rhubarb stalks have a vivid red color and are delicious for desserts and savory dishes. It’s a stable vegetable that has tasty stalks but inedible leaves. Often when I have leftover kitchen scraps, I toss them in the compost pile but was unsure if rhubarb leaves’ toxicity would transfer to garden soil. 

Are Rhubarb Leaves Safe to Compost?

The leaves of a rhubarb plant are poisonous due to excessive amounts of oxalic acid and cannot be eaten. Likewise, the roots of rhubarb plants have no culinary purposes and only medicinal properties. However, rhubarb leaves, as well as the rest of the plant, can be safely composted.

The oxalic acid in rhubarb breaks down quickly in a compost heap and leaves no residual toxins in the compost or garden beds. The composting process easily removes the toxicity and feeds soil microorganisms in the garden. 

The really is no limit to the number of rhubarb leaves that can be composted at once; even a whole rhubarb patch should be fine. As long as there is the correct balance of carbon and nitrogen from the fruit and vegetable garden, the compost from this poisonous plant will be the same as from any other compost pile. 

What is Oxalic Acid and Why is it Dangerous?

Oxalic acid is mild in the terms of how caustic it is but harmful for its effects on the digestive systems and as a kidney toxin. Typically found in leafy green vegetables, they can build up to toxic levels over time and cause serious health effects. 

Low long-term oxalic acid intake can lead to kidney stones as the oxalates bind to calcium and prevent the digestive system from absorbing it. Over time these kidney stones grow, and then surgery or serious painful eliminations of stones will occur.  

Ingesting a large quantity of rhubarb leaves or other sources high in oxalic acid could lead to serious health issues.  There is a likely hood of digestion issues like ulcers and blockages that could require surgery to heal. In extreme cases, it can lead to kidney failure, a life-threatening condition. 

Other Ways to Use Rhubarb Leaves?

Rhubarb Leaves

You can make an organic pesticide if you don’t want to compost the rhubarb leaves or other poisonous plants. The advantage of using your own garden waste to keep your plants safe from pests is obvious. It saves money and works as well as commercial products. It is very good for killing aphids on rose bushes.

The leaves of rhubarb can make natural pesticides if you follow these steps:

  1. Take freshly cut rhubarb leaves and submerge them in cold water 
  2. Leave the leaves in water for 1 to 12 hours to build toxin concentration
  3. Strain out the leaves and collect the concentrated water
  4. Pour the oxalate-rich material into a spray bottle when ready to use
  5. If you spray it on edible plants, do not use it around harvest time, as the chemical is still toxic to humans and won’t have enough time to break down. Avoid using near children and pets. It is ineffective against weeds and doesn’t hurt microorganisms. 

Are There Any Leaves That Can’t Go in Compost?

While rhubarb is entirely safe to compost, some plants should not be. Looking at leaf and plant parts that cause issues with future plants or delay the entire decomposition of plants and not putting them in your compost can help ensure your black gold is always the best for your garden. 

Leaf NameDangers in CompostHow to Fix
Black WalnutPrevents seed germinationLet compost for 1 to 2 years
EucalyptusPrevents seed germinationLet compost for 1 to 2 years
Oak waxy with a long decompositionLet compost for 1 to 2 years
Beechwaxy with a long decompositionLet compost for 1 to 2 years
Hollywaxy with a long decompositionLet compost for 1 to 2 years

Black Walnut – These trees are very large and drop leaves and walnuts. The combination of green and brown materials would seem beneficial to a compost pile. However, the natural color of walnut is to kill any trees or plants, not in its family, and this trait carries into compost and future planting sites. 

When put in compost, walnut leaves can prevent the germination of new seeds throughout the entire compost pile. Adding these leaves and other black walnut plant parts is okay if the compost will age for a long time and give the juglone time to break down. It is also fine if you use compost to enrich walnut trees or mature forests where abundant seed germination is not crucial. 

Eucalyptus – A tall tree that grows well everywhere but sheds tons of leaves and bark, making a huge mess throughout the yard. The plant parts of this tree need to be disposed of in a different area from the compost that will be used for plant propagation. 

Oak – Oak trees contain no harmful chemicals or allelopathic tendencies but do pose a challenge for composts. The leaves of these trees are very wax and can take years longer to break down than other leaves. Oak leaves are big; chopping them finely and using them as mulch is better than composting them. 

Beech – These leaves also have a waxy coating that prevents the leaves’ quick breakdown. These leaves can lay on the forest floor for years, building soil and preventing erosion. If you want your compost ready in a few months, omit these leaves. 

Holly – These leaves have high lignin content, which slows decay drastically. If you have ever looked under a holly bush, chances are you will see years of leaves breaking down slowly. These leaves protect the plant’s roots from extreme cold and prolonged winters but are not good additions to a compost pile. 

How To Safely Compost Rhubarb Leaves? 

The poisonous aspect of rhubarb leaves means that if it is composted, it needs to be done safely. This plant is toxic to humans, cats, and dogs and should be worked deep into the compost pile and never left on top. By the time the pile is turned and the leaves are exposed, the oxalic acid will have deteriorated, and the leaves will be safe.