Leaf Scorch Corrected on a Prunus laurocerasus Screen with a Chempak Sequestered Iron Feed

The leaf pattern that points to iron

On Prunus laurocerasus Rotundifolia, pale tissue between green veins on the youngest leaves is the classic visual clue for iron deficiency. The older leaves lower down often keep a stronger colour because iron is immobile inside the plant. When the roots cannot supply enough, the newest growth shows the shortage first.

This is often confused with drought scorch. Drought damage browns tips and margins, tends to affect leaves across different ages, and usually follows a dry spell. If the soil is moist to spade depth, water stress becomes a weaker explanation. A cheap pH probe reading around 7.6 fits the iron pattern because alkaline soil holds iron in insoluble ferric forms that roots struggle to use.

Root-balled laurel screens are prone to this after planting into clay backfill with free lime in the surrounding subsoil. The plant may have iron present in the ground and still be unable to take up enough of it. The working diagnosis from pale interveinal new growth, green veins, moist soil, and a high pH reading is lime-induced chlorosis. The correction is chelated iron feed; extra watering only leaves the same soil chemistry in place.

Chempak Sequestered Iron and the label rate

Chempak Sequestered Iron is sold as a soluble powder, commonly in 250g and 750g tubs through UK garden retailers. The iron is chelated with EDTA, which keeps it available to plants up to roughly pH 7.5. Above that point, EDTA chelates lose their hold more quickly, while EDDHA-based iron remains effective on more alkaline ground.

A pH reading of 7.6 sits at the upper edge for EDTA. It is close enough for Chempak Sequestered Iron to be a reasonable first feed when the symptoms line up with iron chlorosis, especially where the aim is to correct a laurel screen during the growing season.

The label rate is 30g dissolved in 9 litres of water for about one square metre of root zone. Calculate the dose from the active drip-line area under and just beyond the canopy. Exclude open bed space that the laurel roots have not colonised. If the measured root zone comes to 22 square metres, the total powder needed is about 660g, mixed in stages.

A 9-litre Hozelock watering can is adequate for staged mixing. Dissolve the powder fully before applying it, then refill and repeat until the calculated area has been treated. Pre-wetted soil is important because dry ground can channel liquid feed past the root plate and out through the edges before roots can use it.

Where to pour the feed

Aim for damp ground. Overnight rain can provide that, or the soil can be watered first until the surface takes liquid evenly.

Pour the solution slowly along both sides of the stem line. Keep the main application under the canopy edge and through the strip where feeder roots are active. The trunk collar needs little feed compared with the fibrous root zone spreading out from the plant.

Follow with a lighter plain-water pass. The purpose is to carry the chelate through the top 150mm of soil, where many active feeder roots sit. Heavy runoff wastes the dose, so a slow pass is better than emptying the can in one place.

How recovery should be read

The first useful check is the growth that forms after the feed has reached the roots. Existing chlorotic leaves were built while iron was unavailable, so they may only regain part of their colour. Iron has little ability to redistribute fully into tissue that formed without enough of it.

At inspection points such as 10 to 14 days, look for a dulling of the sharp yellow contrast between veins and leaf tissue. That change can begin at the margins of affected new leaves because fresh iron supply alters chlorophyll production as cells continue to mature. It should be treated as a sign of movement in the plant, not as a requirement that every pale leaf turns glossy green at once.

By around the third week, the most reliable evidence is the newest flush. Leaves produced after feeding should emerge a stronger green if the diagnosis and delivery were correct. Older pale leaves can remain uneven, and that does not cancel the correction if new growth has improved.

Leave those older leaves in place. Even pale laurel foliage still contributes photosynthetic area while the plant rebuilds. Stripping it reduces the working leaf area at the same time the screen needs energy for new growth and root activity.

A second half-rate application can follow six weeks after the first where alkaline soil is the underlying problem. On high-pH ground, a single chelated feed gradually loses effect as the chelate degrades and freed iron precipitates again. Treat the programme as growing-season maintenance, with three feeds between April and August on a full, half, half schedule.

Soil work to reduce recurrence

Chelated iron deals with the immediate shortage in the plant. The pH reading explains why the shortage returns: at around 7.6, the soil chemistry keeps pulling available iron into forms that roots cannot readily absorb.

A full attempt to turn a limey bed acidic rarely holds where alkaline subsoil sits underneath. Aim the work at the surface layer where feeder roots are active. An annual mulch of composted bark or ericaceous-leaning organic matter, laid 50mm deep in spring, slowly nudges that layer in a more suitable direction as it breaks down. It also holds moisture, which helps available iron stay mobile.

Elemental sulphur can be worked lightly into the top 100mm at the manufacturer rate. Soil bacteria oxidise sulphur to sulphate, lowering pH over months. The process needs soil temperatures above about 10C, so autumn treatment may show little visible effect until growth starts again the following spring.

Keep nitrogen modest while correcting iron chlorosis. High nitrogen drives soft green flush and spreads limited iron across more new tissue, which can make visible chlorosis worse on marginal soil. A balanced slow-release granular feed at half the label rate is enough where the screen already has general nutrition.

Keep the shears off the screen

Leave pruning until colour and growth have stabilised. Cutting a stressed laurel screen removes leaf area needed for recovery and stimulates a fresh flush that draws heavily on the iron just supplied.

Reading the next spring flush

A laurel screen can carry corrected growth through autumn because it is largely evergreen. That does not settle durability on alkaline backfill. EDTA chelate degradation on high-pH ground is well documented, and a pH of 7.6 is already at the upper edge of where Chempak Sequestered Iron is expected to function.

Inspect the first spring flush after the autumn sulphur and bark mulch have had time to work. If the youngest leaves emerge chlorotic again, continuing with the same EDTA feed gives a weak return for the effort. The stronger iron product is an EDDHA formulation, which holds to pH 9 and costs several times more per treated square metre. The other route is to treat the backfill pH as the main project, because chelate feeding is only borrowing access to iron until the feeder-root zone changes.

Spring will expose the unresolved part: whether colour comes from the amended surface roots, or the limey backfill keeps taking the iron out of reach.