Research

RHS Curatorial Department and Horticultural Science Department

Peat is an ideal growing medium being low in nutrient and pH status, and consistent in its characteristics. It is formed from anaerobically decomposed plant remains. It develops only slowly and for this reason alternatives are being sought, despite its popularity in horticulture. Alternatives must have the qualities of peat and be available in sufficient quantity.

A range of plants were container planted to demonstrate the use of various alternatives in growing media:

• Streptocarpus 'Falling Stars',
• Pelargonium 'Fireworks Scarlet',
• Verbena 'Lanai Royal Purple'
• lettuce 'Fortune',
• tomato 'Grenadier'

Wood fibre and bark are forestry by-products, particularly from Scots and Corsican pine. Bark is a sustainable product. However supplies are also in demand for mulch and playground safety surfaces. It can lock up nitrogen and has a low water holding capacity.

Green compost is plant material derived from domestic and landscape gardening. Supplies may become greater as restrictions on waste going to landfill tighten, but material quality and consistency is a problem.

Coir is coconut husk dusk and fibre. This is a useful planting material, having a low nutrient status, low bulk density and high water holding capacity. However there are differences in quality between sources, and it is also a non-indigenous product.

Blends of different materials can overcome any disadvantages of particular products.

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