How do I shade plants from strong sun without stunting them?

Shading is a temporary intervention for a temporary problem. Used that way it saves crops and transplants. Used permanently it produces drawn, weak plants that never crop, and it is a sign that the plant is in the wrong position.

Step by step

1. Work out whether the plant actually needs it.Sun-loving established plants in the ground rarely need shading in Britain, even in a heatwave. The genuine candidates are seedlings, recent transplants, salad and leafy crops that bolt in heat, shade-adapted plants in too much sun, and containers on hot paving.
2. Identify the hours that matter.The damaging period is roughly the middle of the day through the early afternoon, when the sun is highest and the air is hottest. Shading for those hours and letting morning and evening sun through gives the plant most of its light and none of the damage.
3. Shade from the direction the sun comes from.Position the screen so it blocks the sun at its peak, which means to the south and slightly west of the plant. A screen directly overhead blocks more light than necessary.
4. Leave air moving.A screen that also traps air makes the problem worse, because still hot air around foliage raises leaf temperature. Keep it open at the sides and clear of the plants.
5. Combine shade with mulch and a deep soak.Shading reduces the demand; mulch and a full soil reservoir supply what is still needed. Doing all three is far more effective than any of them alone.
6. Take it off as the spell breaks.Plants left under shade for weeks grow soft, pale and drawn, and are then more vulnerable to the next hot spell than they were. Shade is for an event.
7. Treat repeated need as a siting problem.If the same bed needs shading every summer, plant something else there or create permanent shade with a shrub or a structure. Improvised screens every year is a symptom.

Tips

• Salad and leafy crops bolt in heat rather than dying. Growing them in the shade of taller crops through midsummer is a standard and effective arrangement.
• Newly planted evergreens and conifers scorch badly in their first summer. Temporary shading and a windbreak through the first hot spell after planting is worth the trouble.
• Damping down a hard surface around containers cools the air locally by evaporation and helps more than it sounds like it should.
• Light-coloured containers stay markedly cooler than dark ones in sun. So does a pot inside a slightly larger pot with an air gap between them.
• Shade cloth is sold by the percentage of light it blocks. For garden use the moderate grades are right — heavy grades are for propagation and will weaken ordinary plants.

Common mistakes

• Shading with anything solid and airtight — Trapped still air heats up around the foliage and the leaf temperature can end up higher than in the open. Shade needs to be permeable or open-sided.
• Leaving shade up all summer as a precaution — Plants under permanent shade grow leggy and pale, flower and crop poorly, and are less able to handle the next hot spell. Shade is a response to a forecast, not a standing arrangement.
• Shading a plant that is wilting from waterlogged roots — Shading treats the demand side, and a drowning plant has a supply-side failure that shade does nothing about. Check the soil before assuming heat is the problem.

Alternatives

• Shade netting: Purpose-made mesh sold by the percentage of light it blocks. The moderate grades are what a garden wants — they break the intensity of midday sun while leaving plenty of light. Durable, reusable and it lets rain through.
• Horticultural fleece over hoops: You almost certainly already have it. A single layer cuts the intensity usefully and passes rain and air. Not as durable in sunlight as netting, but immediately available.
• An old net curtain or a piece of light fabric: Works perfectly well over hoops for a few days. Anything that dapples rather than blocks is doing the right thing.
• A propped board, parasol or chair: For a single plant or a small group, physically blocking the sun from the south side during the hottest hours. Crude, free and effective, and easy to remove.
• Taller planting to the sunny side: The permanent version: sweetcorn, sunflowers, beans on a frame or a shrub casting afternoon shade over things that want it. Plan it rather than improvising it.
• Greenhouse shade paint or blinds: For glass, where the problem is far more acute. Shade paint is cheap and washes off at the end of the season; blinds and external netting are more controllable.
• Moving the plant: For anything in a container, the correct answer nearly always. Two minutes moving a pot beats any shading arrangement.

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