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When I first started composting I had two main issues, one which caused the other. First off, I wanted to compost everything in my kitchen. This meant that, not only did I add a lot of weird things to my compost, but that I always found myself short on browns.
One of the ways I decided to combat this was to try composting pistachio shells. In my mind, pistachio shells were pretty much wood. They looked like wood, they felt like wood, heck, maybe they even tasted like wood.
Long story short, they are not wood and don’t compost anything like it. They are, in fact, a pericarp more commonly known as a hull. While the materials that they are made out of is similar in many ways to wood (they’re both organic after all) they are significant differences in regards to their microscopic structure.
Pistachio shells can be composted but take several years to break down even in a well-managed pile. This can be expedited by crushing the shell beforehand. If you are composting a large number of shells be sure they are unsalted (or you can rinse them) to avoid disrupting your soil’s salinity.
The question, then, becomes whether or not it’s worth it to compost pistachio shells. If you are striving to reduce your waste as much as possible, the answer is probably yes. But if your goal is simply to create large amounts of highly valuable compost quickly, pistachio shells offer about the same to your compost as little tiny bits of super hard wood. In other words, not much.
Concerns with Composting Pistachio Shells
There are three main concerns when it comes to composting pistachio shells in your bin, pile, or tumbler. Let’s hit each one of them and either dispel them or scream in terror:
- They won’t break down. Of course, they will, but they will take forever to do so. We’ll talk about this more in-depth in the next section but, if you want to compost nutshells of any variety, you’ll just have to understand this downside.
- They will ruin the salt balance of your soil. People love to freak out about this but, the truth is, you probably don’t have enough pistachio shells for their salt content to matter. If you eat inordinate amounts of pistachios (or get shells from a restaurant) then you can rinse them before adding them to compost to control the salt.
- They will bleed toxic dyes into your compost. In my opinion, if it shouldn’t go in your compost it probably shouldn’t go in your mouth. While there are some pistachio shells that are dyed they probably won’t have a significant effect on your compost.
With those points standing, I still choose not to compost shells that I feel are overly processed. They offer so little reward in composting that I don’t want to go to the extra effort (or assume additional risk) if the payoff is not more significant.
How to Properly Compost Pistachio Shells
One of the main advantages of composting a pistachio shell is that they add bulk to your compost and (eventually) your garden. As a bulking agent, they perform a similar function to mulch, meaning they loosen up the soil and allow more efficient use of air and water within your garden.
When it comes to composting pistachio shells there are three main avenues of thought:
- Don’t compost them because they add very little to the soil.
- Compost them for a normal time frame and just accept that they won’t be fully broken down when you spread your compost.
- Compost them fully which can take several years.
Of the three, I am partial to the second. If you are trying to win an award for an aesthetic garden it might be a problem to have bits of pistachio shell littered about but, for most of us, it won’t make a difference. Pistachio shells can continue breaking down in your garden or flower beds the same way that they would have done in your compost pile.
It goes without saying here that the smaller pieces that go into your compost, the smaller pieces will come out. Pistachio shells can be either crushed (like with a hammer) or ground before adding. A common way of processing shells and other hard items is to throw them into your food processor for a couple of seconds. This breaks them up which creates more surface area for weathering and microbes to break them down.
So, at the end of the day, of course, you can compost pistachio shells. You don’t see huge piles of them anyway so Mother Nature has obviously been doing it for hundreds of thousands of years. You just have to decide what makes the most sense in your own garden and if it’s worth it to have little bits of them hanging around for years to come.