Reading the Weather Inside Your Garden

On a cold morning, there may be frost on a low stretch of lawn and none on the gravel at the foot of the house. A fallen leaf can lie motionless behind the hedge while another skitters along the passage to the front gate. A pot beside the wall needs water, while a pot of the same size further away still feels heavy. The weather report can be right about all of these places at once. It tells you about a wider area; it cannot tell you exactly what happens on your side of the wall. To get that information, spend a few minutes outside in different conditions and leave a record you can consult when you're choosing where to put a plant, a seat, or a small growing frame.

Draw the features before naming the climates

Start with an overhead sketch. Mark the house, fences, canopy of large trees, paving, low areas, retaining walls, steps and the direction of the ground's general slope. The sketch does not need to be to scale. You want to tell the spot near the bottom of the steps from the one on the other side of the shed. Give promising observation points brief names: Back Wall, Gate, Low Corner, Open Bed. Mark where an overhang extends farther than the wall beneath it. Record any recent changes, such as a neighbour taking down a tree or an old hedge becoming thinner. The character of the garden may have changed faster than its owner has had time to notice.

Now add the conditions you can observe without instruments. Is the soil generally bare or covered by mulch? Where does rain land? Which area has an open view of the sky? A bright corner will not necessarily be warm on a windy morning. A sheltered yard may have cool soil and warm afternoon air. Keep the observations in separate columns rather than trying to mark a corner simply warm or cold. A place can be useful for getting a head start in one season and hard on the same plant in another. Record the date or month as you make each note. You'll want to know whether the trees had leaves at the time and whether the day followed an unusual stretch of weather.

See where frost forms before sunrise reaches it

Compare several points on cold, relatively still mornings. Look where grass, paving, low leaves and raised surfaces frost up first and where the frost stays after the sun reaches other parts of the garden. The low end of a sloped yard can be cooler where cold air collects on calm nights. A wall that absorbs sunshine may warm the nearby area for part of the evening. Ask Extension's note on site temperatures offers examples of both sheltered warm pockets and persistent frost. Treat such examples as patterns to investigate, rather than as predictions for every garden. An exposed corner may cool rapidly on one night and behave differently during a windy cold front.

To learn how much two sites differ, use a pair of comparable minimum and maximum thermometers or sensors rated for outdoor use. Set them next to each other in the same conditions first and see whether the readings agree closely enough for the comparison you want. Then use the same kind of exposure at each point. If one sensor is in sun and the other in a ventilated shade, their numbers won't mean what you think they do. Follow the device instructions about shielding and ventilation. Use a comparable height for the main comparison, and add a low reading separately if you want to know what a seedling near ground level encounters. Swap the devices partway through the observation period if they don't seem to agree. A number that moves with the instrument tells you less about the site than a difference that stays in the same place.

Try recording nights that matter for a decision, such as the week you'd normally move a tender plant outdoors. Note the outside forecast, the minimum temperatures at both points, whether the sky was clear, and whether there was frost visible in the morning. A handful of observations can show a repeated pattern; they cannot redefine a plant's hardiness range. A sheltered corner can reduce some stress but will not turn a long winter into a different climate. If a perennial would be a costly loss, give more weight to local growing experience, regional climate and the variety's needs than to one reading from behind the garage.

Follow the wind that affects the plants

You needn't know the exact wind speed to find a troublesome corner. Stand at plant height beside the edge of a hedge and then in the passage between buildings. Watch where leaves and small branches move and note how the air behaves on either side of a turn. A gap can concentrate flow. A solid wall can shelter one point and create gusty conditions nearby, particularly around the edge. Repeat the walk in a different wind direction. Shelter that works on a mild day may fail when weather comes from a less usual quarter.

Find the evidence the wind has already left behind. Tall stems lean or break in the same direction. Leaves nearest an open corner show wear while leaves a few steps away look fine. A light pot in a narrow gap often ends up out of line. Keep in mind that lean can also follow light and that leaf damage can have other causes. Test a small adjustment instead of assuming a big new screen is necessary. Move one container further back and watch how it behaves through a few windy days. If a seat, bin or parasol is unstable in the location, take it out of use until it can be secured or moved appropriately. Large screens and structures need to be designed and secured for their exposure.

Separate a dry corner from a warm one

Where a bright area sits below an overhang, warm dry air and little rainfall can work together. Elsewhere, a sunny spot may have moist soil because of a change in slope. Check with a trowel in a safe open patch or by feeling the mix inside a container. Look just below the surface and then a little deeper if practical. Compare the day after rain with the end of a dry spell. Brief wetting on top is common after a short shower. It doesn't tell you how much water remains within reach of roots.

If you compare two pots, use similar containers and similar amounts of growing mix. Differences in plant size and composition will still affect the result, so describe the observation as what happened to those pots rather than a definitive rate for the site. Mark the side of a container that feels especially hot or that stays damp against a wall. You might give heat tolerant plants the hotter place while reserving the easier to reach site for pots that need closer watering. A sheltered area is especially useful if a plant can use the conditions and you can care for it without walking a long way with equipment.

An inexpensive rain gauge in an unobstructed place gives you a useful reference. After several showers, compare its readings with what you find under the roof edge and along the exposed border. If the uncovered ground is consistently wetter, the difference is worth recording even if the sheltered corner never feels especially warm. That little comparison can prevent you from treating two planting beds as a single watering zone.

Turn one contrast into an experiment

Suppose the corner near the house repeatedly stays mild after sunset, then feels too hot by early afternoon in July. That spot might serve a movable pot in the cool season and lose the pot to a different position before midsummer. Set a reminder to check it when outdoor meals begin or when a nearby tree leafs out. If you want to use the space for a permanent plant, look for something that can live with both parts of the year. Consider the roots, too. A pot warms and cools differently from open ground. Don't assume the effect of a sheltered wall makes either situation equivalent to the other.

A low area that shows frost early may be a poor place for a tender plant, yet suit a hardy plant selected for the soil and light there. An exposed corner that is difficult for tall flower spikes might be a reasonable place for low growth. Keep the places people use in the picture. If the most sheltered spot is also where everyone has to pass to reach a gate, planting it up to the edge will make the route less useful. There may be a narrow strip to one side that captures some benefit without creating an obstacle. Use the map to weigh those ordinary compromises.

Put a date on your sketch and repeat a few observations when the season turns. By the following year it may show that the corner once called Sunny is better named Bright Until Lunch, that a wind funnel only troubles the garden when the wind comes from one direction, and that the warmest place has the least reliable natural watering. It is harder to remember those distinctions after a long winter or a busy summer. Once they're on the page, decisions about planting and placement can begin with how the garden behaves, even if the only thing for sale at the garden centre is a label that says full sun.