Seed Starting Medium From Around the World

Seed Starting Medium From Around the World

Local gardening with global products

 Gardens are inherently local:  the soil, the sunshine, the rain.  What about seed starting products?  I can trace my seeds to a local organic seed company, and my compost and fertilizer to a local producer.  But growing medium like peat moss and coconut coir aren’t from local sources anywhere near me in Washington.  A quality growing medium is important for successful seed starts.  For organic gardeners who are trying to use sustainable practices, are these growing mediums harvested sustainably and from where do they originate?  

Peat Moss or Coconut Coir

Most premade seed starting mixes contain peat moss or coconut coir.  If you make your own mix, experienced gardeners will suggest including these materials because of their capacity to hold water and aerate the soil.   Don’t forget to use sustainable seed starting pots like reusable trays, coir pots,  compostable pots from newspaper or paper cups, or even “containerless” soil blocks.

For seed starting this season, I decided to compare two products: ready-made peat pellets and coconut coir mix in coir pots.  Vegetable seeds grew in each type of medium side by side.  I highly recommend starting vegetable seeds early.  Planting for a future sunny garden is my productive antidote to the cool and cloudy weather here in Seattle.  Spoiler alert:  both mediums were successful for germinating and nourishing the seedlings.

Where does peat moss come from?​

Scotland Peat Bog
Scotland Peat Bog Credit: Michal Klajban

Is peat moss harvesting sustainable?  Peat bogs are valued as one of the largest soil carbon stores.  It is estimated that they hold up to 30% of the world’s organic soil carbon, keeping carbon out of the atmosphere.  They also provide habitat for diverse species and help to regulate flood and fire protection.  Peatlands are found in many parts of the world, from temperate forests, to the tropics, to arctic permafrost.

About 80% of the peat moss used in North America comes from Canadian peat bogs. The bogs are formed by partially decayed and dried sphagnum moss that is preserved due to anaerobic conditions.  According to Peat and Peatlands, there are 280 million acres of peat bog wetlands in Canada, and less than 74,000 acres of those are currently harvested by the peat industry, primarily for horticultural use.  Although the Canadian peat industry restores all harvested areas, the replanted ecosystem lacks the diversity of the naturally occurring peat bog, and it could take many centuries to rebuild the layers of moss that are removed.

Even though a relatively small percentage of peat bogs is harvested, at their current rate of reduction, peat bogs are being reduced at a greater rate than they are replaced.  Peat bogs increase in depth by about 0.02 inches per year, and at that rate, it takes thousands of years to build up several feet of peat bog.   It is estimated by the USGS that global peat lands are decreasing at an annual rate of 0.05% due to both harvesting and land development.  The largest areas of peat deposits, found in northern Europe, North America, and Southeast Asia, according to the University of Leicester, are being depleted not only for horticulture and development, but also for fuel and clearing land for agriculture.  Recognizing the value of peat bogs, Ireland is making efforts to halt the harvesting of peat lands for fuel and Finland, while continuing to use peat for fuel, is working on restoration. 

As a historic fuel, peat moss has had an important role in some types of whiskey.   Valued for its distinctive smoked flavor imparted during malting, distillers in Scotland have been using peat in whiskey production for centuries.  Even here in the Pacific Northwest, there is a unique essence to the local peat moss on the Olympic Peninsula that gives whiskey its own regional flavor.

While some peat harvesters are attempting to restore what is taken, in some parts of the world peat is removed and burned at an unsustainable rate.  Knowing this, I would not use peat moss as a garden amendment, and limit use to small amounts for seed starts.

Where Does Coconut Coir Come From?

Coconut tree
Coconut tree, Wikimedia Commons

The coconut husk, or coir, is made up of about two-thirds fibers and one-third pith. Fibers are harvested for use in rope, brushes, rugs and other materials. The remaining pith, which is a woody, spongy substance, was considered a by-product waste of the fiber harvest until a process was developed to partially decompose it to be used as a soil amendment. This is the product that is compressed into bricks and sold as coir “peat” that I conveniently picked up at the garden store.  The packaging says that it is from Sri Lanka.

Coir is highly renewable product, given that coconut harvests occur every 45 days, and a typical coconut tree will produce 50-100 coconuts per year. The coir is typically grown by small scale farmers and processed in local mills, according to the FAO

My coir brick is 0.65 kg of coconut pith.  Doing some quick math, based on 100 coconuts per one kg of coir (according to the FAO) of which about 25% is pith, I found that it takes about 260 coconuts to make a single brick!  It is highly compressed, and will expand to many times its size when water is added.  It holds the water, which is great for seedlings that thrive in moist conditions.

Starting seeds

Whether your seeds are growing in peat moss from Canada or coconuts from Sri Lanka,  the goals of the mix are to retain water (so the seeds don’t dry out), to be well aerated (so that the roots have space to spread out), to be sterile (so that it doesn’t grow mold or weeds), and ironically, it should not have a lot of nutrients (so the seedlings don’t have a rush to growth too early).  The pH level should be somewhere around 6-7.

seed starts in peat pellets

Peat Moss Medium with Peat Pellets

An easy way to use peat moss for seeds is with premade “peat pellets.”  These compact and easy to use self-contained planters are composed of sphagnum peat moss wrapped in fibrous netting.  Some manufacturers add lime to adjust the pH to around 5-5.5 and fertilizer to help early growth.  When soaked in water, they expand to several times their size and become little planting pots.  These were easy to use, without the mess of mixing and potting.  The seedlings took root and thrived. 

seedling in peat moss

Coconut Coir Medium and Planting Pots

Coconut coir combined with compost makes a balanced starting mix.  Little pots made of coconut fiber keep it all together.  Like peat moss, coir has great water retention.  It is also sterile and low in nutrients, with 6.0 pH.  Using it in combination with other materials like compost balances the mix for nutrients that seedlings need.

coconut coir brick

The Seedlings are (mostly) successful

The seedlings are happy and green with the help of the peat moss and coconut coir. 

Comparing the two options, the peat pellets excel in ease of use and low cost.  For more control of the ingredients, prettier and larger pots, and a more hands on experience, coconut coir is an excellent choice.  Knowing the origin of the materials has given me a new awareness that my garden has global origins.

seedlings in coconut coir

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