Why is my Griselinia hedge going yellow (or dying)?

You put a Griselinia hedge in for one reason: that clean, glossy green wall down the boundary. So it stings when you're out with your morning coffee and spot a plant or two gone a washed-out yellow, leaves letting go, and the ones either side starting to look a bit crook as well.

Here's the reassuring part before we go any further. A yellowing Griselinia is usually a symptom, not a death sentence, and it's almost always pointing at something happening below the ground rather than anything you did up top. Read the signs right and you've often got time to turn it around.

Isn't it just the wind, or the frost?

That's most people's first guess. And with Griselinia, most people are wrong.

Griselinia is a coastal plant. Its whole reputation is built on shrugging off salt-laden wind that would tatter a lot of other evergreens. So if yours is yellowing on an exposed site, the wind is rarely the real villain. Blame it and you'll treat the wrong thing.

Frost is a fairer suspect, but even then, mostly for show. Griselinia pushes soft new growth early in spring, and a late hard frost can blacken those fresh tips. Looks alarming. In most cases the plant simply drops the burnt shoots and pushes again, sometimes coming back bushier for the haircut. Where frost genuinely bites is on young plants in hard-frost inland country. A first-year Griselinia up around Central Otago, or an exposed inland Southland site, can sit and sulk in a way it never would down on the milder coast. But that's a whole plant checked by cold, not a few yellow leaves.

So when the yellow creeps in, look down, not up.

So what's actually turning it yellow?

Nine times out of ten, the roots. Griselinia has one real weakness, and it's wet feet. It wants free-draining ground, and when it doesn't get it, the trouble starts underground and only shows up in the leaves later, once the damage is well underway.

That gives us a short list of usual suspects, roughly in order of how often they're behind it.

Root rot: the one that takes out a whole run

This is the big one, and the one that actually kills. The disease is phytophthora, a soil-borne water mould that rots the fine feeder roots. It thrives in soggy, heavy ground, exactly the sort of cold wet clay a lot of hedges get planted into.

The tell is the pattern. A hungry hedge tends to pale off fairly evenly all along the row. Root rot picks plants off. You'll see one go yellow, then die back, then its neighbour starts, and it works along the line like a slow fuse lit at the wet end. Often it's the lowest, dampest stretch of the run that goes first. Pull up a dead one and the roots are dark, soft and sparse instead of pale and fibrous.

How do I tell root rot from a hedge that's just hungry?

Look at the pattern, the ground and the roots together.

Root rot: plants dying in sequence, worst in the wet low spots, roots dark and mushy, ground that stays wet for days after rain.

Just hungry: an even, all-over paling across the whole hedge, no plants actually collapsing, roots still firm and pale when you check. That's a feeding or soil problem, not a disease, and it's a far easier fix.

When you're not sure, dig. Five minutes with a spade at the base of a struggling plant tells you more than a fortnight of guessing.

Could it just be hungry, then?

Often, yes, and that's the good-news diagnosis.

A general, even yellowing, oldest leaves first, usually points to a plain nitrogen shortage, common in poor or sandy ground, or in a hedge that's never been fed. A yellowing between the veins while the veins themselves stay green is a different signal, more likely a magnesium or trace-element shortfall. Either way, a balanced feed in spring and some compost worked along the base will usually green it back up over a season.

One caution though. Don't hammer it with high-nitrogen fertiliser heading into the cold months. You'll push a flush of soft growth just in time for the frost to burn it off. Feed in spring, and let it harden before winter.

Did I plant it too deep, or let it go thirsty?

Two establishment mistakes worth ruling out, because both are common and both are on us, not the plant.

Planted too deep, with soil heaped up around the stem, and griselinia can rot at the collar. It should go in at the same level it sat in the pot, no deeper. And a hedge in its first summer has barely any roots to draw on, so a dry spell can leave it thirsty and yellowing even while the ground twenty centimetres down still looks fine. First-year watering isn't babying it, it's the difference between establishing and stalling.

What can I actually do about root rot?

Be honest with yourself about the ground first, because that's the real cause.

If the line sits wet, no spray fixes that for long. Improving the drainage is the only durable answer, whether that's a mounded planting row, some relief drainage, or building the bed up with free-draining material. On a plant caught early, a phosphorous-acid drench or a trichoderma treatment can help it fight back, but treat those as buying time while you deal with the water, not a cure on their own. Plants that have already collapsed are usually best pulled, along with a good spade of the soil around them, rather than nursed along.

And don't just drop a fresh Griselinia straight back into the same wet hole that killed the last one. You'll be back here next winter. If the spot genuinely can't be drained, that's the ground telling you it wants a different plant, not a formal hedge. A wet line suits natives that actually live with their feet in the water, like purei (Carex secta), rather than a clipped evergreen. It's a softer, more swampy look than a hedge, but it'll thrive exactly where Griselinia only ever struggles.

A yellowing Griselinia is the plant talking to you. Nine times in ten it's asking for drier feet or a feed, and both are fixable if you catch it early. Get down and look at the roots and the water before you reach for anything in a bottle.

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