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.
- 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.
- 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.
- Seeds can be started in any grade of perlite, but with smaller seeds, finer grades of perlite would be recommended.
- Perlite is good for greenhouse benches. And as an added benefit, insects and snails do not like perlite!
- Perlite (especially the fine grade) is excellent for drying flowers.
- 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 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):
^All of the above potting mix materials "dry" mixed together.^
^One seedling tray.^
^Seedling trays inside a Polytunnel.^