Nitrogen, phosphorus and potassium - and they tell you what the product is for rather than how good it is.

High nitrogen drives leaf growth and colour, which is a spring or summer feed.

Higher potassium improves hardiness and disease resistance, which is an autumn or winter feed.

Phosphorus supports root establishment and matters most at seeding.

Phosphorus is restricted in some markets because of its effect on watercourses.

Matching the ratio to the season and the objective matters more than the brand.

By calibrating the spreader and applying half the rate in two passes at right angles.

Overlapping passes doubles the rate and scorches the turf.

Missed strips stay pale for weeks and are just as visible.

Both persist for the rest of the season once they appear.

Calibration is against the product's stated rate rather than against the spreader's own markings.

Two half-rate passes at right angles cancels most of the error either way.

Undissolved prills sitting on wet leaf, drawing moisture out of the tissue.

The damage appears as scorched patches or stripes within days.

Applying to wet grass in hot weather is the classic mistake.

Watering in after application dissolves the prills and moves them into the soil.

Over-application concentrates the same effect.

Controlled-release products are far less prone to it, which is part of their argument.

Frequently yes - fertiliser applied to dormant turf is largely wasted.

Nutrients that the grass cannot take up leach past the root zone.

That is both a waste and an environmental problem.

Soil temperature and active growth matter more than the calendar date.

Applying before rain moves the product in; applying before heavy rain washes it away.

Reading the season rather than the diary separates good results from average ones.

Increasingly - restrictions on timing, buffer distances from water and on some products exist in a growing number of markets.

Nutrient run-off into watercourses is the driver.

Phosphorus restrictions are the most widespread example.

Professional users often face record-keeping obligations that domestic users do not.

Rules differ between countries and sometimes between regions within one.

Checking the local position is worthwhile before applying near any watercourse.

They are convenient and they constrain timing to whatever suits both components.

The ideal moment to feed and the ideal moment to treat weeds rarely coincide.

The result is usually a compromise on one or both.

They also apply herbicide to the whole area including where there are no weeds.

For a lawn with scattered weeds, spot treatment plus a straight feed is more effective.

For a heavily infested lawn the combined product is a reasonable single operation.

Sealed and dry - it absorbs moisture and cakes solid once a bag is opened.

Caked fertiliser will not flow through a spreader and cannot be applied evenly.

Breaking it up rarely restores usable prill size.

Resealing opened bags and storing off concrete floors helps considerably.

Buying to the season rather than to the discount avoids the problem entirely.

Spreaders should also be washed after use, since residue corrodes them quickly.