What are some sustainable alternatives to peat for potting compost?

Question

I've just finished writing the tag wiki for organic and was thinking about wider issues of sustainability. Perhaps the best area where I could improve things personally, would be to use an alternative medium for seed trays. At the moment I use peat-based potting soils -the kinds that are sold for germinating seeds.

I currently use a mixture for larger plant types, and I could easily avoid the peat based composts and use more of the coarser wood-based composts.

But what could I use for starting new seeds with? It would have to be nutritionally rich, and also fine grained. Seeds are primarily peppers, but I do start other things from seeds.

I think I've heard of people using coir (derived from coconut husk hair), but I think I heard it was too fissile? Does anyone have any experience or have any other alternatives I could try in spring?

I don't recall seeing anything in the big box garden suppliers here in Texas - so I would probably have to go to a nursery.

Answer 1

Below seeding, potting (container) mix comes from, BBC Leeds, Gardening with Tim and Joe, "Super Bumper Mega Edition 25 Jul 11" or via direct link to MP3 - Super Bumper Mega Edition 25 Jul 11, start listening at 9mins:20secs into podcast:

• 8 parts "good" quality (screened) compost
• 1 part Perlite

A little more information about using Perlite as a plant growing medium:

• Rooting materials

Perlite is another excellent propagation material. It is lightweight and provides good aeration for rooting. Perlite makes one of the best rooting materials when mixed with an equal volume of peat moss.

• Using Perlite in Potted Plants

Conclusions

1. Perlite is one of nature's best media for growing plants. It does not appear to make any difference which grade is used except with certain plants like orchids.
2. It is possible to grow most plants in perlite alone, although usually the finer grades and medium grades will work better and require less water.
3. Seeds can be started in any grade of perlite, but with smaller seeds, finer grades of perlite would be recommended.
4. Perlite is good for greenhouse benches. And as an added benefit, insects and snails do not like perlite!
5. Perlite (especially the fine grade) is excellent for drying flowers.
6. Perlite is ideal for outdoor containers. They can be moved around easily because perlite in the mix lightens it, besides improving drainage.

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With reference to:

• Compost Heap via Kew Royal Botanic Gardens

• Compost Corner via Kew Royal Botanic Gardens

Today (2011-08-05) I heard back from Kew, regarding what they meant by "peat substitute". Below is the article they directed me to:

• Potting with coir

We use coir as the basis for our potting mix in the nursery, named "Kew Mix 3". It was developed in the late nineties and consists of:

• Coir (45%)
• Silvafibre (commercially available well rotted leaf-mould) (45%)
• Loam (equal parts sand, silt and clay)(10%)
• Kieserite (Trace) and a slow release fertiliser (15.9.11)

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Yesterday (2011-07-31) I attend a "Potting Mix" class put on by Gateway Greening, was an excellent class, well worth my time. Below are some of my notes:

• A good "Potting Mix" is made up of 3 basic parts:

  • Water retaining material.

  • Drainage material.

  • Plant food (fertilizer) material.

• Water retaining material is traditionally Peat Moss, in the US it's mostly Sphagnum Moss imported from Canada. One thing to be aware of is, nearly all Peat Moss has a low pH (usually somewhere in the range of 4.0 to 5.0), therefore this needs to be taken into account when mixing your own potting mixes. Generally speaking the "sweet spot" for nearly all potting mixes is a pH of 6.5

  • One alternative water retaining material is Coir. Can be bought in a "brick" format, excessive salt can be an issue depending on the process used. If the label of the "brick" shows excessive salt content, the coir should be washed "thoroughly" before use.

• Drainage material is traditionally coarse sand.

  • Some alternative drainage materials are, Perlite, Vermiculite and Rice Hulls.

• Plant food (fertilizer) material is traditionally compost.

  • One alternative plant food (fertilizer) material is Worm Castings.

Below is a "general" potting mix that Gateway Greening have settled on (at least for the time being, as they also continually carryout experiments with different formulas):

• 5ft³ (0.142m³) of Peat Moss (sieved) - Water retaining material.

• 5ft³ (0.142m³) of Perlite - Drainage material.

• 5ft³ (0.142m³) of Worm Castings (sieved) - Plant food (fertilizer) material.

• 1 quart (1.1 Litre) of (finely crushed) Lime Stone - Added to increase the pH level, remember, Peat Moss has a low pH (usually somewhere in the range of 4.0 to 5.0).

• 1 quart (1.1 Litre) of Bone Meal - Added to increase the amount of Phosphorus available to the newly germinated plants eg Help with root growth.

The above mixture is then thoroughly dry mixed together. Once that is completed, water is added to the dry mixture via a fine mist. This is a two person job, as one person drops the dry mixture through the air, the other person adds the water to the falling mixture. The potting mixture should end up moist (like a damp sponge), but not so wet that when you squeeze it water runs out.

The above potting mixture quantities make enough potting mix for at least 50 seedling trays, and works out at about 38¢ per tray.

Two weeks after the seeds have been sown in the potting mix, they receive a "weak" Fish based fertilizer feed. This is done to ensure the newly germinated plants have enough nutrients (food) in the soil to help them grow properly.

• We were also (given) pointed toward an excellent potting mix reference, it basically contains all of the above, plus a lot! more information:

  • Potting Mixes for Certified Organic Production from NCAT Sustainable Agriculture Project

Below a few photos I took during the class (click images to enlarge):

^All of the above potting mix materials "dry" mixed together.^

^One seedling tray.^

^Seedling trays inside a Polytunnel.^

Answer 2

In The New Organic Grower, Eliot Coleman addresses the issue of peat on p118:

I do not share the anti-peat moss sentiment I occasionally hear expressed. The [...] movement began in Europe where [...] they are at the point where finding substitutes for peat makes sense.

[...]

Of the peat lands in North America, only 0.02 percent are being used for peat harvesting. On this continent peat is forming some five to ten times faster than the rate at which we are using it.

On the same page, he talks about potential for using kenaf fiber as a planting medium.

I refer to this only because I don't think it's urgent to find a peat replacement. I do think it's a great idea to experiment with ways to move away from peat; locally sourced materials are a better long term sustainable solution.

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For my growing, I use peat only as part of a mix for making soil blocks -- following either the recipe in New Organic Grower or something similar from web (they're all about the same).

My (peat-free) recipe for potting soil is:

• 5 gal sifted garden soil
• 5 gal sifted mature horse manure compost (we use a wood-based bedding product, and the compost has some of the desirable properties of peat)
• 5 gal coarse sand
• "sprinkling" of equal parts lime, greensand, and rock phosphate -- strength depending on what I'm potting

Depending on what I'm planting and how much I have, sometimes I substitute sifted garden compost for all or part of the horse manure.

I arrived at this recipe because the major components are free, it uses what I have on hand (it's basically impossible to run out of anything but fertilizer), and it has been very successful for getting seedlings off to a strong start.

Based on what you have available locally (this is the essence of sustainability), experiment starting with my recipe or something similar and develop your own potting recipe. Nothing that comes from a Big Box is really all that sustainable. Y'all got horses in Texas? :)

Answer 3

I find that equal parts soil, compost, and worm castings works well, and I don't have to buy the materials, sustainable or otherwise. Don't forget that perlite/vermiculite have to be mined and shipped, which burns fossil fuels.

Answer 4

In response to those up-thread who seem to think that peat extraction in Canada is not a big deal, I have to say:

I have stood on the edge of Provincial Area of Natural and Scientific Interest (ANSI) in southern Ontario and watched the peat being extracted. It broke my heart. The bog in question lay just outside the border of a Provincial Park, and the Park and Nature Conservancy Canada had been negotiating to purchase it. The land owner wanted more money that was being offered, and as a pressure tactic had stepped up the rate peat extraction from the bog. At the same time, he was still allowing the Park Natural Heritage Education staff to access the parts of the bog that were not being mined for our own educational purposes, so I can tell you there were many regionally and provincially significant plants growing in it. Extracting the peat from this bog was destroying an ecosystem that was 10 000 years in the making.

Talking about peat on a continent wide basis is really rather irrelevant. You need to know where the peat you are using is being extracted from. Most of the peat in North America is found in vast peatlands in boreal forest. This is far different from the situation that I observed, which was an isolated kettle bog in southern Ontario. The species living in the bog had nowhere else to go when their home was destroyed. The bog provided a rare habitat type in Ontario south of the Canadian Shield. Other southern Ontario bogs are also subjected to the same destructive land use.

We cannot restore a bog to it's original state once it has been mined out, at least not on a human time scale. So please, if you're going to use peat, try to determine it's source.

Answer 5

Has anyone tried using palm husk? It's light weight, can shed water, can retain water. Very high availability. Easy to grow. The boots could be incorporated along with the trunk. I have been told by a few palms intake sand as they grow and a reason for dulled chainsaws when pruning and felling. Walnut husk, peacan husks, sweet gums, egg corns. Substainablily to my central area in florida with all things considered I believe ph levels would bring more work unless potting acid loving plants.
Our natural sandy loam soil acts like a perlite substance but very acidic. Leaf mold itself could also be use. Food for thought.