Fertiliser for ornamentals

A wet winter and cold late spring make growers use topdressing, Mike Beardall and Maureen Keepin report.

Topdressing was used this year to help stock recover from long winter - image: Compo
Topdressing was used this year to help stock recover from long winter - image: Compo

Severe winter weather and extreme rainfall across the UK have led to ornamental plant producers having to boost plant nutrient levels with topdressing and foliar feeds. As a result, many have had to re-evaluate the way they use slow-release fertilisers for container-grown plants.

"This winter has really taken us by surprise," says Adrian Hillman, director of Rushfields Plant Centre in West Sussex, which won the Horticulture Week award for best retail promotion of roses in 2006. "Plants have needed some extra feed to replace nutrients that have been leached out by the cold and wet.

"We use an all-year-round programme of coated slow-release fertilisers incorporated into the growing media - some offering a threeto six-month lifespan and others from nine to 12 months. The speed of breakdown and release is vital so we choose our fertilisers carefully, tending to use Osmocote products that have specific timings."

Andy Johnson, managing director of Wyevale Container Plants in Hereford, says the winter weather has led to a reappraisal of the needs of nursery-grown stock. "The severe winter has resulted in root and leaf damage and the cold weather means compost has not warmed up, reducing the uptake of nutrients," he adds. "We are experimenting with slow-release blends but the immediate action is to apply topdressing and liquid feeds to promote growth."

Manufacturers are constantly improving and widening the choice of fertilisers for nursery plant production and Johnson's company has been carrying out trials for Scotts Professional on a new breed of slow-release fertiliser, Osmocote Exact Hi-End 12-14, due to be officially launched at Four Oaks in September (see box, p35).

Scotts Professional fertiliser manager Andrew Wilson explains that every situation is different and advice to nursery owners is tailored to plants' specific needs and local conditions. "Because we produce slow-release fertilisers with varying formulas we are able to produce the right solutions for growers," he adds. "All have their individual problems depending on the type of stock they grow and the part of the country they are in."

He recommends assessing plants in early spring to identify over-wintered plants that would benefit from topdressing. "Our Osmocote Topdress sticks to the top of the growing media and stays put even if the pot is blown over," he points out. "Recently growers have been able to make efficiency improvements by speeding up application and reducing labour costs through the use of Fertil applicators. These are popular with staff because they can apply the feed without having to bend down."

Johnson says: "We have been battling to keep stock alive during these past few months and the base level slow-release feeds have not been picked up by plants because of the cold. Growers all over the country have experienced the same problems and we will look at all sorts of solutions based around different timings of introducing slow-release fertilisers to the growing medium."

Tree production has escaped serious disruption from the weather, according to Hossein Arshadi, director of Hillier Amenity Division and head of tree production and container trees at its 250ha site in Petersfield, Hampshire. He monitors slow-release fertiliser levels by taking soil samples and has been surprised to find that nutrient levels have not been as badly affected as they feared.

"We are running approximately three weeks behind this year with fertiliser application because of the late spring," he says. "We put down a slow-release base dressing and will topdress in late spring and again in early summer."

As a general base dressing, Arshadi uses Floranid Permanent (16-7-15) at 160-250kg per hectare depending on the needs of the tree type and field conditions. This will last through the growing season. "Topdressing is largely nitrogen but it has been so wet we have not been able to get on the ground as early as we would like," he says. "We tend not to put any fertiliser in our container-grown trees. They are in a peat-free compost that we liquid feed."

Mike Butler, UK technical sales manager at German company Compo, which manufactures Floranid Permanent topdressing and Basacote controlled-release fertilisers, says the late cold spring has called for topdressing to give container-grown plants a boost. "Lower salt-containing materials mean there will be no scorching in nursery stock and this is a major factor in plant production," he adds.

Jack Dunckley of Birchfield Nursery in West Sussex says they have had good results from Sinclair Horticulture's Sincrocell pellets. "Slow-release fertilisers have taken longer to kick in this year because of the cold compost conditions but we also use fish, blood and bone as a quick booster and that gives the plants strength," he says. "A lot of growers are going down the organic route at the moment and this is one way of giving plants good leaf growth and root production."

Nursery consultant John Adlam of Norfolk-based Dove Associates says the range of controlled-release fertilisers (CRF) gives growers plenty of options. "This is very useful in nitrate-vulnerable areas where leaching needs to be controlled," he notes. "This long cold winter has led to a lot of leaching of nutrients from container-grown stock and topdressing is going to be widely used to help plants recover.

"The best topdressings adhere to the surface of the compost but must not be in contact with the stems. They must supply the correct amount of nutrients at the right time, relative to the needs of the particular plant. The product should break down into a powder over a period of time and become part of the growing medium through irrigation or rainfall."

His advice to growers is to choose the right controlled-release fertiliser for the plants and conditions. Topdressings are useful because they can work in advance of the CRF. Among those that he has seen used are Novatec, Floranil Permanent and Triabon, all from Compo.

Scotts Professional produces Osmocote Hi-End using Dual Coating Technology - with a percentage of the granules having several coats to delay part of the nutrient release to match requirements. It also produces Agroblen, a controlled-release topdressing applied in spring that lasts from two to three months or from five to six months.

Sincron, from Sinclair Horticulture, is a compacted micro-granular topdressing fertiliser formulated to provide nutrients for container-grown stock in the second and later years prior to sale. Gem Horticulture produces LaterOn, a wetting agent with a controlled-release topdressing fertiliser in granular form for both the start of and during the growing season.

Two more products for topdressing are Nitrophoska and Mascot Planting Plus. The first is a complex mineral fertiliser available in four formulations. The second is a topdressing for hardy nursery stock, providing nitrogen and phosphates in a slow-release form, together with potash and magnesium.

Vitax produces Q4, an extended-release fertiliser with organic nutrients, increasingly used as a topdressing and suitable for a wide range of plants grown on both loam-based and soil-less composts.

Liquid feeds based on composted ingredients include the Soil-tech Solutions system from Fargro, based in Littehampton, West Sussex, and the Growing Solutions system from Martin Lishman in Bourne, Lincolnshire.


A 12-14-month formulation of controlled release fertiliser Osmocote Exact Hi-End 12-14, providing hardy nursery stock with season-long nutrient release, will be launched at Four Oaks in September.

"Benefiting from Dual Coating Technology, an additional layer on the granule provides a predefined and delayed release pattern," explains Scotts fertiliser manager Andrew Wilson.

"This sophisticated fourth-generation Osmocote product provides programmed release. Starting off low at the beginning of the season while plants establish, nutrient release increases mid to late season, when plants profit."

Promoting efficient fertiliser use, Osmocote Exact Hi-End 12-14 ensures growers use nutrients effectively and efficiently over the whole season. "This is good news for plant quality as well as the environment," says Wilson. "Also, plants are less likely to need a nutrient top up during the season so it can save time and labour costs."

This formulation is also recommended for sensitive plants and crops grown under glass or in high temperatures. "In trials, we've seen less disease pressure because plants are more vigorous," adds Wilson. "This new formulation delivers what hardy nursery stock needs - improving crop quality, yields and ultimately return on investment."


Fertilisers are part of the armoury of landscapers who have to maintain their planting despite the harshness of weather conditions. "The winter has hit many projects badly," says award-winning designer and landscaper Sue McLaughlin of Henfield, West Sussex.

"Mulching and woodchips have protected roots to some extent but water and frost damage has meant that a fertiliser boost has been needed to encourage new roots and foliage.

"A lot of us are using fish, blood and bone as a tonic for plants, but granular products with slow-release properties are gaining in popularity because we can rely on them to continue performing on sites that get little attention.

"The winter has hit plants such as Phormiums and Cordylines quite badly and a lot of hardy shrubs such as Ceanothus have had foliage burned off by the frost.

"Granular fertilisers and liquid feeds applied when growth starts should increase plant strength. But some plants in garden schemes will have been lost and landscapers will be checking last year's plantings to see what damage the winter has done."

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