Slow release fertilisers are sold on how long one application lasts, from around 12 weeks up to 5 or 6 months, and that figure is worth checking before the NPK numbers. Match the release window to how often you can realistically get back out to feed, then let turf type and job pick the analysis.

How long do you want one application to last

Most of the range holds for around 12 weeks. Nutrilong V90 20-5-10 (2% MgO, 70% V90, 1-2mm) suits fine turf, Nutrilong V90 26-6-12 (2-3mm) gives general turf a stronger green-up over the same period, and Command Slow Release All Season Fertiliser (13-0-26) uses methylene urea to hold for the same 12 weeks with a lot more potassium and no phosphate.

Go up a tier and the Nutrilong V180 coating stretches that out considerably. Nutrilong V180 29-4-8 (1-2mm, 83% slow release) runs for around 24 weeks, and Nutrilong V180 29-4-9 (2-3mm, 76% slow release) holds for 5 to 6 months from a single application between March and June. That is close to half the growing season covered by one spread, which is where slow release genuinely earns its price on large sites: fewer passes, less product carried around, less risk of missing a feeding window because the crew was somewhere else.

Nitrogen for growth or potassium for hardening

Release speed only tells you how long the feed lasts, not what it does once it is there. Command High Phosphate All Season Fertiliser (16-12-8 + Zn + TE) is built for seeding, overseeding and newly laid turf, where phosphate drives root development rather than leaf growth. Command Balanced Spring & Summer Fertiliser (15-6-15) gives all three nutrients together for the main growing season, while Command Zero Phosphate Spring/Summer Fertiliser (16-0-16) drops phosphate out entirely, useful on turf that already tests high for P and does not need more of it. Velscape Slow Release Tree & Shrub Fertiliser (4-19-10 + 8% MgO) is a different job again: weighted towards phosphate and magnesium and matched to how slowly woody plants use nutrients, running for around 24 weeks.

Fine turf or general turf decides the granule

Homogeneous 1-2mm granules, most of the Command range and some Nutrilong analyses, are sized to settle below turf cut short: greens, tees, fine lawns. Coarser 2-3mm granules, the Velscape range and other Nutrilong grades, suit lawns, parks and pitches cut above 10mm and spread more predictably from a standard broadcast spreader. A fine granule on long turf, or a coarse one on a green, mostly just wastes the extra cost of the slow release coating, so check granule size against cut height before the NPK ratio.

The percentage of slow release nitrogen in the analysis is worth reading too, not just the headline NPK figures. A 40% slow release grade and an 83% slow release grade can share a similar first number and still behave very differently on the ground, since the higher figure means more of that nitrogen is locked into the coating rather than available straight away. The product page for each grade states the percentage and the expected longevity together, and the two should be read as a pair.

Which slow release fertiliser for which job

For fine turf through the main season, Nutrilong V90 or Command Balanced Spring & Summer both hold for 12 weeks. For general lawns and parks, Velscape All Season Slow Release Fertiliser (15-5-10) does the same job on a coarser granule. Where you want to feed once and genuinely leave it for most of the season, the Nutrilong V180 range is the only one built for that. New turf and overseeding want Command High Phosphate rather than a general slow release grade, and trees and shrubs need Velscape Tree & Shrub, not a turf product at all.

If two products look interchangeable on paper, check the longevity figure and the granule size before the NPK ratio. That is usually what actually decides whether it is the right bag for the site, and the team can talk through a specific programme if you want a second opinion.

Frequently asked questions

Is slow release fertiliser worth the extra cost over a standard grade?

Not always. On smaller sites you can reach easily and feed often, a standard release grade is usually cheaper overall. The saving from slow release is in labour and site visits, so it tends to pay off on larger or harder-to-reach ground rather than a small lawn.

Can I apply a spring analysis late and have it release slowly into a sensible autumn feed?

No, release speed and application window are different things. A spring/summer formulation applied in December will still be spring/summer in its NPK balance, just released slowly, so it will not do the job an autumn analysis is built for.

Do I need to water in a slow release fertiliser?

Most granular slow release grades need rainfall or irrigation to start breaking down the coating and releasing nitrogen. Check the specific product page for how soon after application, since this varies between the methylene urea and coated grades.