Controlled release fertilisers: These are almost always granules of inorganic fertilisers coated with a porous material such as sulphur or synthetic resin. Water enters the granule and the fertilisers leach out into the surrounding soil. The warmer the soil, the faster the leaching; this corresponds to plant growth which is faster in warm weather. By varying the thickness of the coating granules can be designed to feed plants for different periods of time.

A compound fertilizer granule encased in a skin that allows water to enter, dissolve some fertilizer and exit at a known rate (temperature related); “Osmacote” 4 month used in compost for bedding plants or hanging baskets; “Osmacote 12/14 month used in compost for container growing of shrubs.

Benefits: Removes the need to liquid feed plant after the effect of the base fertilizer has worn off when used as part of the base fertiliser as release is temperature controlled reduction in leaching.

As the feed is released at a controlled rate, the risk of root scorch is removed. If used in the production of bedding plants it gives them a good shelf life and boost when planted out.

Limitations: Considered expensive; Slow initial release of plant foods; You cannot so easily manipulate the plant’s reaction to differing feeds (growing fuchsias); If mixed in stored compost the release of nutrients can reach harmful levels; If weather is unseasonably warm, feeding can continue (Wimbledon tennis courts).