Planting out in a heatwave: what I learned the hard way

2024: Slugmageddon

The year before last was a bad one for slugs. Really bad. So many newly planted things got wiped out that I started thinking of it as Slugmageddon. Plug plants that had been fine on one visit were gone by the next.

The solution I landed on was metal rods bent into mini frames over the beds, with netting draped over them. Slug pellets underneath — which the netting kept the birds from getting to — and for the most vulnerable plants, individual plastic cloches to give them a chance to establish before the slugs found them.

A UK allotment at sunset showing multiple beds — one with white plastic cloches protecting young plants, another with green netting draped over it, a metal arch in the background — 2024. Cloches on one bed, netting on the next, slug pellets underneath both. Not pretty, but it worked.

A plastic cloche covered in condensation protecting a young plant in allotment soil, blue slug pellets visible around it, netting frame visible in the background at dusk — The close-up version. Blue slug pellets inside the netting, cloche over the most vulnerable plants. A lot of effort for something that should just go in the ground.

The cloches were imperfect — I could not always get to the allotment as often as I wanted to, and a closed cloche in warm weather will cook a plant just as surely as no water will. So I used them sparingly, for the first week or two after planting, then removed them once things were established enough to hold their own.

2025: The same timing, a different year

Last year I planted marigolds out in April, same as always. The netting frames went up, the slug pellets went down, and the weather that spring was ordinary — mild, some rain, nothing extreme. By summer, every bed had a dense continuous border of orange. The whole plot looked like it was on fire.

A raised allotment bed with a dense orange marigold border all the way around, a metal netting frame over the bed protecting the plants inside — 2025, early summer. The marigolds are in, the netting is up. It worked.

Nasturtiums in full flower in the foreground of a raised bed, with a dense orange marigold border visible behind, a metal arch frame overhead — Midsummer 2025. Nasturtiums in the foreground, marigolds all round the back bed. The nasturtiums draw the blackfly onto themselves and away from everything else.

Butterhead lettuce heads growing inside a raised bed completely surrounded by enormous orange French marigolds in full bloom — This is what it looks like by midsummer when the planting works. The marigolds have grown to dwarf the lettuce. Every allotment holder who walked past stopped to comment.

Multiple raised allotment beds all lined with dense orange marigold borders photographed at golden hour, the whole plot glowing — 2025 at peak. Every bed, every border, orange all the way round. This is what I was trying to get back to.

2026: What I found when I got back

I planted marigold and yellow calendula plugs out in April, along the edges of the raised beds. Dense borders, the same as last year, when the whole thing looked brilliant by July. Two days after planting, we had a run of hot days — genuinely unusual for April. I could not get to the allotment to water. When I finally went back, every single one had gone.

A single fried marigold plug with dried red stems and shrivelled foliage in allotment soil, backlit by low evening sun — This is what I came back to. The stems had turned red and the leaves had curled in on themselves. There was nothing to save.

Up close, the damage was worse. The stems had gone red and brittle, the foliage had crisped up and pulled inward. Some still had a little orange colour left in the flower buds — just enough to make it sadder. I planted at almost exactly the same time last year and they thrived. But last year was a normal April. This year the heat came early and the roots, which had never been outside, simply had nothing left to draw on.

Close-up of fried marigold plugs along a raised bed edge, stems turned red and brittle, a little orange colour remaining in the dried flower buds — The detail of it. A little orange left in the buds — not enough.

Ordering again

I pulled them all out, ordered more plugs, and waited. When they arrived, I did things differently. I watered the beds first. I planted in the evening. I watered each one in immediately after going in the ground, properly — not a sprinkle but a real soak at the base. And I checked the forecast before committing to anything.

The result is a border that is thinner than planned. I could not replace them all like-for-like and the gaps show. But they are alive, which is more than I can say for the first batch.

A raised allotment bed from the side showing orange marigolds dotted along the border in evening light, with the allotment in the background — The second attempt, in evening light. Sparser than the plan. They are staying in.

Top tip

Plant plugs out in the evening, not the middle of the day. Water the bed first, plant into moist soil, water in thoroughly straight after. If it is going to be above 20°C for several days and you cannot water, wait.

Everything else that went out

Tomatoes, cucumbers, courgettes, and sunflower seeds all went in around the same time. It is now another heatwave — June this year seems determined — so I am watering everything on every visit and hoping. The courgettes look settled already. Courgettes seem to shrug off almost anything. The tomatoes are upright against their canes. The cucumbers have their climbing frame and are beginning to reach for it.

French marigold plugs are usually available from garden centres through June and July. The season is long enough to recover from a setback like this — marigolds flower from whenever they go in right through to the first frost, so a June replanting still gives you four months of border.