Guide to carrying out peat-free trials

Comparing plants grown in different mixes in a peat-free salvia trialDifferent peat-free growing media are suited to different types of plants and environments, and carrying out trials of peat-free mixes is the best way to find the right one for you and the way you grow.

The RHS peat-free team has put together this guide to help you carry out effective trials of different peat-free growing media in your commercial nursery setting. The team are coordinating trials at eight UK partner growers, as well as running further trials at RHS Hilltop.

Planning your trial

Step 1 – Speak to different growing media suppliers to find the most suitable mixes for your crop and environment. This will be your shortlist for trialling.

Step 2 – Plan your trial layout. You will need to lay out your trial pots as randomised blocks within a plot, to control for any effects that a plant’s position may have on its quality. We recommend a minimum of six pots per block. See the diagram below for guidance.

Step 3 – Consider the control. The control mix should be your normal growing media, and at least two different peat-free mixes should be trialled alongside the control.

Our recommended trial layout is shown below. Each block contains six pots of the same growing media, and blocks are laid out in a randomised array within the experimental plot.

Recommended trial layoutBefore you start

  • Use fresh growing media, which is stored in a cool, dry place.
  • Ensure all pots are clearly labelled with their growing media and date of potting.
  • All plants should be potted at the same time, use the same irrigation method, and be in the same environment in terms of rainfall, humidity and temperature.
  • Use stock plants at the edges of your trial plot to avoid edge effects.
  • Download this record sheet with score cards (210kB pdf) to keep track of your trial and the results.

During the trial

  • Analyse growing media with an electrical conductivity meter at the start, end and at intervals throughout the trial.
  • Treat your peat-free mixes exactly the same as your controls.
  • Take measurements of all plants on the same day and time where possible, and at regular intervals throughout the growing cycle.
  • Water according to plant requirements and to meet best practice. Wetting agents can be very useful with peat-free media, but make sure to also use these on your controls. They come as granules or liquid, so can be added before or after potting.
  • Lift pots to assess water levels at the base of the compost. Peat-free mixes may look dry on top but can be moist lower down.
  • Use additional fertiliser as required for all plants on a block, just as you would with your normal mix. Keep records of what fertiliser was added and when. If plants are outside, rain and temperature may affect leaching and controlled release fertiliser.

Other top tips to get the best from your trials

  • Growing media deteriorates over time. Use it as soon as possible after purchase and store any excess in a cool, dry place.
  • Be aware that plants may root later in peat-free media.

Comparing root development of peat-free plug plantsDownload your free trials guide and record cards to score your peat-free mixes here (210kB pdf).

Questions about carrying out your trials? Get in touch.

See also

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