How do I map the microclimates in my garden?

Nearly every plant that dies in a garden dies in a place, not in a garden. The same variety thriving on one side of a lawn and failing on the other is the normal experience, and the explanation is almost always a difference in light, water, wind or overnight temperature that nobody measured. This is how you measure it, cheaply and without instruments.

What you'll need

• A sheet of paper and a pencil
• A phone camera (optional)
• A min/max thermometer (optional)

Step by step

1. Draw the plot roughly to scale.Boundaries, house, sheds, trees, big shrubs, paths, beds. It does not need to be beautiful — it needs to be recognisable and to have room to write on. Photograph it and keep a copy, because you will annotate the original into illegibility.
2. Mark north.Use a phone compass. Everything about light in the garden follows from this, and a surprising number of people have it wrong by ninety degrees.
3. Do the summer light survey.On a sunny day, photograph the garden from the same fixed spot in the morning, at midday and in the late afternoon. Shade in all three shots is full shade; shade in one is part shade. Mark the boundaries on the map.
4. Do the winter light survey.Repeat it in midwinter. This is the step almost everyone skips and it changes the picture completely: the low sun throws shadows several times longer, so borders that were sunny in July are shaded all day in January.
5. Map the water.After heavy rain, walk out and mark where puddles stand and where the ground squelches. In a dry spell, mark where the soil cracks and where plants wilt first. Also mark the strip along any wall where the eaves keep rain off entirely — that rain shadow is often the driest ground on the plot.
6. Map the cold.After a frost, mark where it lingers longest. If you have a min/max thermometer, move it around and record overnight minima in three or four positions across a run of frosty nights.
7. Map the wind.Tie ribbons or strips of plastic bag to canes at head height around the garden and look at them on a windy day. Gaps between buildings funnel and accelerate wind; corners create turbulence; the lee of a permeable hedge is calm for a surprising distance.
8. Name the zones and plant to them.You will usually end up with a hot dry strip against a sunny wall, a sheltered sun trap in a corner, a cool moist shaded side, dry shade under any tree, a wind-funnelled patch, sometimes a frost pocket, and the open middle. Each takes a different plant list and a different watering regime.

Tips

• Take the photographs from a fixed marked spot every time. Comparable images are worth far more than better images.
• The strip of ground under the eaves of a house can stay dry through a wet British winter. If a plant against a wall keeps dying and you keep blaming the cold, check whether any rain reaches it at all.
• Do the exercise before you buy plants for a new garden, not after. A year of survey costs nothing and saves more than a year of replacements.
• Zones do not have to be big. A metre-wide strip against a sunny wall is a genuinely different climate from the border two metres away, and it is where borderline-hardy things go.

Common mistakes

• Surveying in summer only — Summer light is the least useful season to survey, because almost everywhere gets some sun when the sun is high. The winter map is the one that tells you where evergreens and winter interest can go.
• Treating the map as permanent — A tree grows, a neighbour builds an extension, a hedge is removed. Redo the light survey after any significant change and every few years anyway.

Questions people ask