When container growing first became popular, loam-based growing media was used. It was usually of clay origin — containing lots of trace elements — so all that was needed was the addition of nitrogen (N), phosphorus (P), potassium (K) and possibly a bit of lime. These would have been supplied from straight fertilisers. And straights tend to be soluble in water so nutrient not taken up by the plant would be washed away and require regular replacement either by liquid feeding or as a top-dressing.
The loss of nutrients through leaching is a waste of money as well as potentially damaging to the environment. But, in any case, the advent of peat as a substrate — and more recently peat-reduced and peat-free composts — has meant changes in the way nutrients are supplied as well as in the ratios required. Most growers now buy in ready-mixed composts and want a fertiliser that lasts the life of the crop — the “feed and forget” theory that means growers can concentrate on other aspects of production and essentials such as marketing.
The higher percentages of non-peat raw materials now used in composts are also having an effect on the way we feed plants. Some products, such as bark, tend to use some nitrogen themselves, despite being as mature as possible. Bark and most organic materials also tend to be high in potassium. “This is true of green-waste products, which can have relatively high conductivities,” says Scotts technical adviser Dr Jim Smith. “All this has to be taken into account when choosing a fertiliser regime.”
UK nursery-stock producers are renowned for growing a wide range of species. The requirements in terms of compost mixes are kept to a minimum to keep things simple. It’s a case of a few mixes being made to suit a great many species. And because of the “feed and forget” factor, plus the bonus of shelf life, 95 per cent of nurseries will use controlled-release fertilisers that release nutrients according to temperature and so reflect the natural patterns of plant development and growth.
“The standard would be a container nursery stock (CNS) general compost with 4.5kg/cu m of a 12- to14-month controlled-release fertiliser. This has to be a compromise and some species will have too much and others too little — as a result, quality suffers,” says Dr Smith.
However, there are controlled-release fertilisers that will mimic the growth patterns of different types of plants. Low-start fertilisers encourage rooting and then release more as the season progresses. This is ideal for early-planted conifers and also for autumn-planted crops that do not want to be too soft in the back-end of the year. There are also high-start products that suit deciduous crops needing to put on a lot of growth in the early part of the season and then ease up during flowering and seeding. This type is particularly useful for late-planted conifers that are already in growth and requiring instant nutrients. There are also some exciting new developments, as Dr Smith explains.
“A new development is Osmocote Protect,” he says. “It has a dual coating that stops release of nutrients for the first couple of months while the first coating breaks down and then releases as normal. This means crops can be potted on out of season during the winter months without the loss of fertiliser associated with the weather. The fertiliser then kicks in during the spring.”
In addition, there are products that contain a proportion of dual-coated granules. This means that nutrients can be targeted at different periods of growth. “At present these are NPK nutrients, but with this technology specific elements such as potassium can be supplied to the plant during flowering,” explains Dr Smith. “The potential is endless, but it does mean growers have to be more aware of the way particular species grow and utilise the most appropriate fertiliser for the job.”
Making fertiliser even more efficient and effective is important, but development rarely comes cheap. Many growers are currently concerned about costs. And the price of nutrition is rising.
Sinclair Horticulture technical marketing manager Mike Daley says: “We have seen substantial rises in the price of raw materials and certainly a number of products have gone up quite dramatically in the past year or two.”
Sussex-based distributor Fargro points out that increases in energy costs for refining and manufacturing processes are putting certain fertilisers under considerable price pressure. In addition, there are fertilisers disappearing from the marketplace.
Nursery stock consultant John Adlam confirms that the energy requirements in the production of some fertilisers are quite high. Added to that is the increasing cost of transport.
“We have to remember that fertiliser prices have been held down over the past few years by companies sourcing product from eastern Europe rather than traditional sources,” says Adlam. “I think the present situation is due to rising energy and transport costs. It is another thing to worry about. Every price rise is a major problem because the market is not as profitable as it used to be. Any costs that go up squeeze margins.”
Doing his sums, Adlam points out that a tonne of controlled-release fertiliser can cost around £3,300. “You can do an awful lot of liquid feeding for that money,” he suggests.
In Holland, growers do liquid feed. But the production of just a few species per nursery is well suited to such nutrition, unlike the UK where many dozens of subjects fill every nursery. And there are downsides to liquid feeding: no shelf life when the plant goes to the garden centre and the dilemma of needing to feed the plants even though they may not actually need irrigating.
Despite the cost, the use of controlled-release fertilisers will be essential in the future — especially when environmental factors are added to the equation. “There is considerably less fertiliser lost to the ground using controlled-release products, so they are more environmentally friendly,” says Dr Smith. “In nitrate-restricted zones they can be used when other fertilisers cause problems. Dual-coated products would be particularly suitable in these zones.”
And even in the field we are likely to see controlled-release fertilisers take a hold. Dr Smith says: “Cost has restricted their use on large-scale holdings, but environmental issues will dictate that conventional fertilisers are no longer acceptable. Europe is already using these products and seeing benefits.”
Have you registered with us yet?
Register now to enjoy more articles and free email bulletinsSign up now