Like many of you, I’ve been using Spaghnum peat (the decaying remains of Sphagnum moss) for seed starting for many years. Perhaps you are also like me in that I had never really given it a second thought because it is what I grew up with, not to mention it is so commonly used in blend-your-own and prepackaged seed starting mixes. But about a year ago, I started to read up a little more on peat, and discovered that there are some real concerns over the sustainability of horticultural peat use. This set in motion my desire to try coconut coir (the ground hulls of coconuts) as a more sustainable alternative to peat.
The Sustainability Debate
Here’s the deal with peat: It is mined from a bog, meaning the upper, still-living layers of moss are removed, the peat is harvested, and the bog is then “restored” by returning the living layer that was removed. There are a number of environmental concerns with this practice (the mining process severely disrupts the bog’s delicate ecosystem, and it also releases large amounts of carbon dioxide that are otherwise trapped, or “fixed,” within the bog), but the crux of the sustainability debate is that even with the best restoration efforts and controlling the pace at which peat is mined, it will still take hundreds of years for the bog to regenerate peat that has been mined. So while technically sustainable, “hundreds of years” is a long time.
Coir, on the other hand, is a byproduct of processing coconuts that are harvest for food, oil, etc. In other words, it is already being produced to satisfy the world’s appetite for coconut and using it for horticultural purposes keeps it out of the waste stream. It is produced in Indonesia and in parts of Mexico and South America and it is not without its own environmental impacts, but because coconut trees produce season after season, it is a more sustainable alternative.
Of course there are other factors to consider as well. Most of our Sphagnum peat comes from Canada, which is much more local than Indonesia, but peat is prepared and packaged to maintain a slight moisture content (otherwise it is nearly impossible to rehydrate), which means it is heavier and bulkier to transport (by truck, usually) than coir, which can be completely dehydrated and compressed to a fifth of its original volume for lighter and larger shipments (by sea, usually). There are jobs, and local economies to consider, and there is also availability (last year I couldn’t find coir locally at all).
As is often the case when trying to be as “green” as possible, there are often few truly perfect solutions, and you’ll have to weigh the options for yourself to determine which arguments are more compelling. Fortunately, there is a lot of interesting and lively debate on this subject to help you make an informed decision.
Using Coir for Seed Starting
Coir can be used in the exact same way peat is used in seed starting. There are coir pellets and coir pots that you can purchase and fill with the planting medium of your choice. Coir dust can also be used as either a component of a seed starting mix or on its own as a planting medium.
As I have already mentioned, coir can be completely dehydrated and compressed to about a fifth its original volume. These bricks of coir dust must be rehydrated and allowed to expand prior to use. Some coir bricks come with a perforated plastic bag for expansion, but I found them to be messy and less effective than simply placing the brick in a bucket or sink. Water is then added until it is fully expanded. It only takes a mater of minutes if you are using warm water (about 10 minutes if you are using cold water). It has a cell structure that allows for impressive moisture retention. When expanded, coir has a rich, soil-like quality that feels substantial, yet is still soft, fine-textured and light.
If you are using it as a component in your own seed starting mix, the moisture it retains is just the perfect amount to make your seed starting mix easy to work with and keep dust to a minimum. It can also be used as a soil amendment in your garden beds and container gardens. Unused coir can be stored for future use.
Comparing Coir and Peat
Let’s break it down and take a look at how coir compares to peat in seed starting practice:
- Rich in potassium and a number of micro nutrients
- Neutral pH
- Holds moisture incredibly well; easy to re-wet when it dries out
- Can sometimes contain higher salt concentrations (commercially available coir has been greatly improved in this regard)
- Availability may be limited locally
- Not a source of nutrients
- Acidic pH
- More difficult to wet; retains less moisture
- Can actually restrict germination of some seeds (peppers, in particular)
- Readily available; commonly used
While I couldn’t find it locally last year, this year my usual garden center carried a good stock of coir bricks, as well as a variety of different sized pots and starter pellets. In fact, the coir pots were the only plantable pots on the shelves this year. I am encouraged by this trend and hope that it means coir products will become even more accessible in the future. Cost-wise, the coir pots were pretty much right in line with their peat counterparts, but the bricks of coir dust ended up being about a dollar or two more expensive than a comparable quantity of peat.
My initial reaction to using coir in my seed starting this year is extremely positive. I will have a better sense as the season goes on, but based on my initial experience, I am pretty much sold on using coir as an alternative to peat. I feel better knowing that I’m making a more sustainable choice, but even more so, I truly believe that coir is a superior product for the reasons I’ve outlined above.
A Third Option
I would be remiss if I did not mention that there is another option in the sustainability debate. If you are not thrilled with the environmental impacts of either coir or peat, you could opt to start your seeds without the use of either product. Personally, I find the qualities they bring to a seed starting medium to be quite helpful in successful seed starting, but they are not essential. Locally sourced compost can add some of the same qualities to your seed starting mix as peat and coir. If you forego the use of a lighter material, just be sure to watch for signs of compaction or seedling stress, which might require more frequent potting up of your seedlings.
What are your thoughts on sustainability and seed starting? I’d love to hear from you and find out what factors you weigh when selecting materials to use for seed starting and other gardening activities.