Potting Soil for Delphiniums
John Innes Potting Compost
Seed compost:
- 2 parts sterilised loam
- 1 part moss peat
- 1 part sharp sand
The loam and peat is put through in 3/8 in (9mm) sieve.
To each bushel (8gal/36l) is added:
- 1.5 oz (42gm) superphosphate
- 3/5 oz (21gm) ground limestone
Potting Compost:
- 7 parts sterilised loam
- 3 parts moss peat
- 2 parts sharp sand
The loam and peat is put through a 3/8 in (9mm) sieve.
To each bushel (8gal/36l) is added
- 3/4oz (21gm) ground limestone
- 4oz (110gm) 14-14-14 Osmocote
This makes John Innes Potting Compost No. 1. For a richer mix simply double the quantity of John Innes Base to make No. 2 or treble it to make No.3
CORNELL MIXES
From Hobby Greenhouses in Alberta
Agdex 731-5
The Cornell peat-Lite Mix* is formulated for growing topical plants. The Foliage Plant Mix ** and the Epiphytic Mix** formulas are adapted specifically for their respective plant types and are modifications of the original peat-lite mix.
Cornell has used Osmocote 14-14-14 and Peters 14-7-7 fertilizers with the tropical plant mixes with good results. Other fertilizers are omitted with the exception of dolomitic limestone and 20 per cent superphosphate which are added to adjust the pH and to maintain adequate phosphorus levels. A trace element mix is added to assure a balance of minor elements. Trace element mixes can be purchased from specialty gardening centers.
* “Cornell Tropical Plant Mixes” by Russel C. Mott
**L.H. Bailey Hortorium, Cornell University, Ithaca, New York
Cornell Peat-lite Mix
Mix 1/2 cubic meter each of sphagnum peat moss and perlite or vermiculite. Add 6kg dolomitic limestone, 2.4 kg ammonium nitrate, 1.5 kg superphoshate, and 0.3 kg potassium chloride (omit if using vermiculite).
Cornell Foliage Plant Mix
The Cornell Foliage Plant Mix was developed for those plant that need a growing medium with high moisture-retention characteristics. Plants having a fine root system or possessing many fine root hairs are included in this group.
| Material | 1 cubic meter |
| Sphagnum peat moss (screened 1/2 inch mesh) | 0.5 |
| Horticultural vermiculite (No. 2) | 0.25 |
| Perlite (medium grade) | 0.25 |
| Ground dolomitic limestone | 4.9 kg |
| Superphosphate 20% (powdered) | 1.2 kg |
| Fertilizer (10-10-10) | 1.6 kg |
| Iron sulfate | 0.4 kg |
| Potassium nitrate (14-0-44) | 0.6 kg |
| Granular wetting agent | 0.9 kg |
Cornell Epiphytic Mix
The Cornell Epiphytic Mix was developed for plants that require good drainage, aeration and have the ability to withstand drying between waterings. Plants having coarse, tuberous, or rhizomatous roots are in this category.
| Material | 1 cubic meter |
| Sphagnum peat moss (screened 1/2 inch mesh) | 0.33 |
| Douglas, red or white fir bark* (about 0.5 cm size) | 0.33 |
| Perlite (medium grade) | 0.25 |
| Ground dolomitic limestone | 4.2 kg |
| Superphosphate 20% (powdered) | 2.7 kg |
| Fertilizer (10-10-10) | 1.5 kg |
| Iron sulfate | 0.3 kg |
| Potassium nitrate (14-0-44) | 0.5 kg |
| Granular wetting agent | 0.9 kg |
* Fir bark comes from Douglas fir, white or red fir, or redwood, ground and screened to a definite size. Finally ground bark (about 0.5 cm) has a dry weight of about 200 g per liter cube. Fresh bark has a pH of about 5.0. Upon weathering, it becomes slightly more alkaline. The bark contains some nutrients, but these will not meet the requirements of growing plants.
