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I've just finished writing the tag wiki for 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.

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have a read of these: Successful Seed Starting: Timing is Everything & Successful Seed Starting, Part II & Successful Seed Starting, Part III, then let me know what you think. Maybe we can then put the relevant parts together & post as an answer. –  Mike Perry Jul 26 '11 at 19:01
    
@mike: Alas not very useful. only the second one mentions the growing medium, and that says to use a peat mix - ie. What I'm doing now, and not sustainable. –  winwaed Jul 26 '11 at 19:07
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why not sustainable in seed starting mix? I understand why it's not sustainable when people throw huge amounts into their landscape ie Use as organic matter to improve their soil. –  Mike Perry Jul 26 '11 at 19:12
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Beware of advice from people who have something to sell you. Those six-packs are junk. Cut-off 1/2 gal milk cartons (free) are 1000x better for starting tomatoes than six-packs, which are so small that they'll be root-bound a week after germinating. Best is using soil blocks, but I haven't found a usable soil block recipe without peat, so that doesn't help you any. –  bstpierre Jul 26 '11 at 20:54
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@winwaed, some additional reading material: Starting Plants Indoors From Seeds, especially Germination media –  Mike Perry Jul 26 '11 at 21:41

4 Answers 4

up vote 11 down vote accepted

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:

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.

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.

With reference to:

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

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)

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.

  • 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.

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

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

Seedling Tray
^One seedling tray.^

enter image description here
^Seedling trays inside a Polytunnel.^

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Yes the standard mixes usually include some perlite and/or vermiculate and your first link includes quite a bit, but the second looks like it is proposing >50% or mixes. Presumably a 100% mix would require some kind of fertilizer mix. –  winwaed Jul 28 '11 at 2:04
    
@winwaed, "Presumably a 100% mix would require some kind of fertilizer mix," as far as I'm aware, the same applies to 100% peat ie Use in agriculture: "Peat can store nutrients although it is not fertile itself." –  Mike Perry Jul 28 '11 at 2:31
    
@winwaed, also from Using Perlite in Potted Plants: 1-Plots and pots containing fine, medium, and coarse perlite have had exactly the same weight and size as those using traditional peat mixes. Many tests have proved there should be no hesitation in using finer grades, and that 100% perlite could be used and be just as successful as traditional peat mixes. –  Mike Perry Jul 28 '11 at 2:32
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Technically speaking, perlite is not sustainable either. At the current rate of depletion, world reserves will only last another 300 years or so... ;) –  bstpierre Jul 28 '11 at 2:59
    
@bstpierre, then the question has to be, is 100% "good" quality screened compost (maybe with a small amount of coarse sand added to help improve drainage) the answer? Similar to your answer below. –  Mike Perry Jul 28 '11 at 3:55

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.


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? :)

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Thanks. So it sounds like my query is less relevant for the US (where I'm currently located). I remember it becoming a big issue in the UK in the late 1980s, which made me think of the query. I'll keep the question open for European members. –  winwaed Jul 26 '11 at 21:07
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@winwaed, you might be interested in this, Compost Heap, & this, Compost Corner. I have asked Kew what they mean by "peat substitute". I will post back if I receive an answer back from them... –  Mike Perry Jul 27 '11 at 0:03
    
@Mike: "turned occasionally with a JCB". That's a big compost heap! –  winwaed Jul 27 '11 at 1:06
    
@win: John Deere turns mine, it's just easier on the back! –  bstpierre Jul 27 '11 at 1:21
    
@Mike: definitely interested in hearing their answer. –  bstpierre Jul 27 '11 at 1:22

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.

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Good point about fossil fuel usage. –  itsmatt Jun 7 '13 at 13:19

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.

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Hi and welcome to the site. While your points are interesting and useful they don't answer the question, which is "what are the alternatives". If you can edit your answer and offer some alternatives (or at least address the question specifically) then your answer becomes more valid (in the context of Q&A), will possibly get upvoted, and will thereby get more visibility. –  Tea Drinker Feb 5 '12 at 16:59

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