Growing Media

Growing media: selecting ingredients other than peat

Preamble

Because it has never been our policy to buy growing media as an off-the-shelf proprietary product, moving into the terrority of "other than peat" required a fresh assessment of the available "building blocks".

In whatever media, we try to understand what is going on in the root zone, and we freshly mix on-site using bulk ingredients and varying proportions of nutrients, pH adjusters, etc. For many years the bulk ingredients have been 80% peat and 20% wood fibre.

For our trials, we chose the following raw materials as potential building blocks: pine bark, coir, miscanthus, bracken, wood fibre, shredded and composted material generated on-site, and not least, loam.

We are fortunate in having on our site a large supply of loam. This began as top-soil removed prior to constructing our large reservoir and container beds. On this we establish mown grass, rotavate the top 25mm and push into windrows for summer maturation before taking under cover for shredding and heat pasteurization.

Approach

To try and gain an understanding of the properties and performance of alternative materials, extensive in-house trials are underway to identify suitable materials for the complete replacement of peat. We started out in early 2023 with 17 formulae for "general stock" (ie most Trees and Shrubs), 3 for Conifers and 14 for Ericaceous. Needless to say we are getting many surprises! Key characteristics we are tracking are water holding, air-filled porosity, nutrient retention, pH stability, aeration, density, capilliarity, resistance to "slumping"; then, practically, "flowability", "cohesiveness", over-wintering success, flower-bud-initiation propensity and friendliness to beneficial bio-flora. Some of these could not be known in the first growing season. At the same time, we are calculating the aggregate road / rail / sea miles incurred by the ingredients of each formula.

Scope

Subjects we included are Cytisus Porlock, Sambucus Black Beauty, Ceanothus Repens, Photinia Little Red Robin, Lonicera Rhubarb & Custard, Lonicera Hall's Prolific, Campsis Tropical Summer, Clematis Nelly Moser, Clematis montana Elizabeth; then as to deciduous trees Amelanchier lamarckii, Ginkgo and Liriodendron. We included four Conifers, three Erica, and Calluna Dark Beauty.

Procedure

To gain a rapid initial indication of responses, we ran a trial, potting in March 2023 including Nemesia (which we do not produce commercially), and in May 2023 the most promising were replicated in larger numbers in a 3 litre container. As was to be expected, results were variable, but promising.

Decisions

Postively, since January 2023 all our rooting media for cuttings has been 100% peat-free. We do have some experience as we first tried this in 2011!

Our policy for these rooted cuttings is as follows: for Shrubs and Conifers, pot all into peat-free compost in 9cm liner size. These will then in 2025 be potted into 3 litre peat-free: we are building the base of the "inverted pyramid".

As to Erica and Calluna, only a proportion (the most strong-growing varieties) will go into 9cm or 1 litre pots peat-free in May 2024. The remainder will go into peat/bark until we have more confidence.

Observations and Reflections April 2024

Perhaps the bigest surprise of all is the health of the plant roots in most formulae - having been out of doors for the last three and a half months, under very high rainfall conditions. This is positive. Though not surprising, it is noticeable how much impact the growing media has on the propensity to initiate flower bud. This too is a useful tool. Based on what we have learnt from the above experiments, we have to date potted more than 1,600 plants into peat-free compost, including 10 litre Magnolia and Hamamelis, as are the whole of our rootstock potting for grafting this summer and next winter.

Informing our Customers

Items which are peat-free will be indicated on our website and in all our sales literature as part of the product description.

Anticipated Timescale for 100% Peat-free Production

We are encouraged by results so far, but many of our lines have not yet been included in our trials. While these trials continue, our priority will remain that all our output is of top quality.

G. John Richards 18/04/2004