Frost risk, soil temperature, rainfall and UV — what you actually need to know before heading into the garden, and an instant forecast for wherever you are.
Check today's gardening weather →Soil temperature is the most overlooked factor in gardening. Air temperature can feel warm while the ground is still cold — and seeds planted into cold soil will sit dormant, rot, or germinate poorly. A cheap soil thermometer (probe type) is one of the best investments for a food grower.
| Soil temp | Verdict | What to plant |
|---|---|---|
| Below 5°C | Too cold | Nothing. Soil is too cold for any reliable germination. Focus on planning, pruning and structural work instead. |
| 5°C – 7°C | Marginal | Hardy crops only: garlic, onion sets, broad beans, overwintering brassicas. Germination will be slow. |
| 7°C – 10°C | Suitable | Peas, spinach, lettuce, carrots, parsnips, beetroot. These cool-season crops thrive from this point. |
| 10°C – 14°C | Good | Most vegetables and annual flowers. Ideal for direct sowing outdoors. Roots establish quickly. |
| 15°C+ | Ideal | All vegetables including warm-season crops: courgettes, beans, tomatoes (in sheltered spots), sweetcorn. Maximum germination rate. |
After a warm sunny week, you might feel it is warm enough to plant everything out — but the soil can lag several weeks behind the air temperature, particularly in shaded areas or on north-facing slopes. Raised beds warm up faster than ground level. Black or dark-coloured pots absorb heat and warm soil much more quickly than terracotta or white containers.
Covering beds with cloches, fleece or black polythene 2–3 weeks before planting can raise soil temperature by 3–5°C, significantly extending the growing season. Remove covers on warm days to allow rain to penetrate and air to circulate.
Frost is the event that can undo weeks of careful growing in a single night. Understanding when it is a genuine risk — and how to protect plants when it is — is one of the most valuable skills in gardening.
A standard forecast showing 2°C overnight may still produce a ground frost — the temperature at ground level can be 2–3°C lower than at the measurement height of 1.2 metres. On still, clear nights with no cloud cover, radiative cooling can drop ground temperature well below the forecast air temperature. This is why clear, calm nights in spring are the most dangerous for late frosts.
Horticultural fleece draped over plants on cold nights can protect against frosts down to about -3°C. Cloches offer similar protection. Never use plastic sheeting directly against plant leaves — it conducts cold rather than insulating. Move pots under cover or against a wall (which retains some warmth). Mulching the soil surface with bark or straw insulates roots even when the air above freezes.
Seedlings raised indoors or in a heated greenhouse need a gradual transition to outdoor conditions — this is called hardening off. Place them outside in a sheltered spot during the day for a week, bringing them in at night. Gradually leave them out for longer until they are ready to plant permanently. Skipping this process and planting straight from a warm propagator into cold garden soil is one of the most common causes of seedling failure.
Rain is essential for the garden, but the right amount at the right time makes all the difference. Too little and plants stress; too much at the wrong moment and you can do more harm than good trying to work in the garden.
Light, regular rainfall is the gold standard. It keeps soil moist without waterlogging, penetrates deeply with time, and reduces the need for irrigation. After a few days of light rain, established beds rarely need watering for a week or more.
Established trees and shrubs can tolerate drought well, but newly planted specimens, vegetables, salad crops and lawns struggle quickly. Water deeply and infrequently rather than little and often — this encourages deep root growth. Focus water at the base of plants rather than overhead to reduce evaporation and fungal disease risk.
Sustained heavy rain (more than 10 mm/day for several days) can waterlog soil, driving out oxygen that roots need to function. In waterlogged soil, roots suffocate and rot even in plants that otherwise love moisture. Raised beds and well-structured soils drain much faster. If water is pooling on the surface for hours after rain stops, drainage improvement (grit, organic matter, or raised beds) is worth prioritising.
The single most common mistake gardeners make is digging or rotavating wet soil. This destroys soil structure — compacting clay soils into hard lumps that can take a full growing season to break down. Wait until the soil no longer sticks to your boots before digging. A simple test: pick up a handful of soil and squeeze it. If it holds a solid shape and does not crumble when you open your hand, it is too wet to work.
UV is the one weather factor most gardeners consistently underestimate for themselves. Spending 3–4 hours digging, weeding or planting on a sunny summer day accumulates significant UV exposure — often without feeling hot.
Seedlings and young plants moved directly from indoor conditions into full sun can suffer leaf scorch — the leaves bleach and develop papery patches. This happens because indoor-raised plants have not developed the wax layer on their leaves that protects against UV and desiccation. Harden off in a shaded spot first, gradually introducing more sun over 5–7 days before moving to a full-sun position.
On sunny high-UV days, plant out in the late afternoon rather than the morning. This gives seedlings the cool of the night to settle their roots before facing the heat and UV of the following day. Water in well after planting and consider using a temporary shade cloth or upturned pot lid to protect the plant for the first 24–48 hours if the weather is very sunny and warm.
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