Why has my evergreen gone brown on one side?

Evergreens keep their leaves through winter and go on losing water through them, while frozen or cold soil stops the roots replacing it. The result is a plant that dries out in the middle of a wet British winter, and the pattern of where it browns tells you exactly which version of that happened.

Step by step

1. Ask whether it appeared overnight or over weeks.Frost damage appears within a day or two of a specific cold night. Wind scorch develops gradually over a cold, dry, windy spell and is often not noticed until it is extensive. Salt damage appears in late winter after gritting.
2. Look at which part of the plant is affected.Frost: the youngest growth at the tips and the top, and the side that faced the open sky. Wind: one flank, from top to bottom, with a hard vertical edge where the shelter of a wall, a building or another plant begins. Salt: the lower part of the plant on the side facing a road, path or drive, in the splash zone.
3. Work out the prevailing wind.In most of Britain it is from the south-west, but a garden's own funnels matter more — a gap between two buildings, a side passage, the end of a hedge, the corner of a house. A brown flank facing one of those is wind, not disease.
4. Rule out the disease look-alikes.Browning that appears in irregular patches all over the plant rather than on one side, with dieback of individual shoots, points at disease or root problems instead. Box turning brown in patches with black streaks on the stems is box blight. Conifer hedges browning from within with no clear direction may be drought at the roots, a dead root system, or in leylandii the effect of cutting back into bare wood.
5. Check the roots and the ground.Evergreens brown badly when they cannot get water, which includes frozen ground, a rain shadow next to a wall, and a plant that was never watered in its first two summers. Push a finger or a trowel into the soil on the affected side and see what is there.
6. Wait before cutting anything.The dead outer growth shelters live buds behind it. Cut nothing until new growth shows in late spring — often May or June on evergreens — and then cut each stem back to living tissue.
7. Know which plants will reshoot from bare wood and which will not.Yew, box, holly, laurel and privet generally reshoot from old bare wood and can be cut back hard. Leylandii, cypress, thuja, most other conifers, lavender and rosemary largely will not — a brown patch on a conifer hedge often stays brown permanently, and the answer is a screen, a replanting or patience while surrounding growth fills in.
8. Build shelter rather than treat the plant.A permeable barrier — a hedge, a slatted fence, netting — filters wind and reduces its speed for a distance of several times its height downwind. A solid fence creates turbulence on the sheltered side and often makes things worse.
9. Protect the vulnerable ones over winter.Fleece or netting on the windward side of a newly planted evergreen for its first winter or two, removed once it establishes. Water evergreens in late autumn before the ground cools, since a plant going into winter dry is the one that scorches.
10. Wash salt off where you can.If the browning is from road salt or de-icer, water the ground thoroughly in early spring to leach it through, and consider a low barrier or replanting with salt-tolerant species along that edge.

Tips

• Evergreens planted in autumn on an exposed site frequently scorch in their first winter and recover perfectly. Spring planting gives them a full season to root first.
• Bronzing across a whole conifer or a grass in winter is often deliberate — nandina, some thujas and many ornamental grasses colour up in cold weather and green again in spring.
• Conifers shed their oldest inner needles every autumn. Brown needles falling from inside the plant are normal; brown on the outside of the canopy is not.
• A brown patch on a leylandii hedge is the strongest argument there is for not letting it get too big in the first place, since it cannot regrow from the bare wood you would need to cut into.

Common mistakes

• Cutting a scorched evergreen back in February — You remove the shelter for the live buds and you cannot yet see what survived. Wait for growth.
• Erecting a solid fence for shelter — Solid barriers create turbulence and eddies on the leeward side. A permeable screen slows wind more effectively over a much greater distance.
• Feeding a scorched plant to help it recover — The problem was water and wind, not nutrients, and a stressed plant with damaged foliage cannot use fertiliser.
• Assuming brown means dead — Scorched foliage is dead; the buds behind it usually are not. Scratch a stem for green before writing anything off.

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