How do I photograph a plant problem so someone can actually diagnose it?

Most requests for a plant diagnosis fail on the photograph rather than on the problem. A tight close-up of one blotch tells an expert nothing, because half of plant diagnosis is position — which leaves, which side of the plant, whether it relates to the veins, what is above it and what is around it.

Step by step

1. Shoot the whole plant first, in its position.Stand back far enough to include what is around it: the wall, the tree overhead, the pot, the path, the neighbouring plants. Position explains an enormous number of problems and the wide shot is the one people always miss out.
2. Then shoot the affected part still attached.Show where on the plant the damage sits — top or bottom, old growth or new, one side or all round. A leaf photographed on a table has lost the single most diagnostic piece of information about it.
3. Take a sharp close-up of the damage.Get close but stay in focus, and tap the screen on the damage so the camera focuses there rather than on the background. Include the edge of the affected area and some healthy tissue next to it — the boundary is what identifies a leaf spot.
4. Turn the leaf over.Almost everything that sucks sap lives on the underside, and downy mildew fruits there. If you send one photograph only, this is frequently the useful one.
5. Include a healthy leaf from the same plant.It gives a colour reference and settles whether pale really is pale. Without it, nobody can judge colour from a phone photograph.
6. Photograph in bright shade, not in sun.Direct sun blows out the highlights and hides exactly the surface detail that matters. Flash does the same and adds reflections. Overcast light or the shaded side of a building is ideal.
7. Put something in the frame for scale if size matters.A fingertip, a coin or a pen. Insect identification is nearly impossible without a sense of whether the thing is one millimetre or five.
8. Write down the four facts that go with the pictures.What the plant is, how long it has been there, when the symptom started and how fast it spread, and what changed recently — repotting, feeding, a move, spraying, a cold night, building work nearby.

Tips

• Take the same shot again in a week from the same position. Whether the damage is spreading separates a live infection from finished damage, and no single photograph shows that.
• For anything smaller than a grain of rice, tape a white card behind the leaf and tap the leaf sharply over it. Photograph what lands.
• Most phones will focus much closer if you use a small amount of digital zoom rather than pushing the lens right up to the leaf.
• The RHS, local horticultural societies and county gardening groups will look at photographs. So will a good independent nursery, and they are looking at the same problems all week.

Common mistakes

• Sending a single tight close-up — It removes position, scale and context, which is most of the diagnosis. A blotch photographed alone could be six different things.
• Picking the leaf before photographing it — A detached leaf loses the information about where on the plant it grew, and it starts wilting and changing colour immediately.
• Photographing only the worst leaf — The worst leaf is often the least informative, because everything has run together. Early damage shows the pattern most clearly.

Questions people ask