Heritage Seed Library horticulturist Sophie Atkins shares some of the ways the team are managing our National Collection during the hot weather.

Alternative text should describe the visual content of the image. — Aphids are multiplying quickly on our brassicas in the polytunnels

With temperatures in the polytunnels reaching 57°C - it’s been a real struggle to be inside them this summer. We try to go in first thing in the morning and follow the shade around as much as possible.

In the glasshouse, we’ve added shading to the roof to protect seedlings from direct sunlight and reduce evaporation. And we’ve extended the time the irrigation systems are running to avoid scorching leaves when the sun is fully out. We’re hand watering any plants that still appear to be struggling

Summer survivors 🔗

We’re noticing a wide range of reactions from the different varieties we’re growing this year. For example, broad bean ‘St. Gorran’s’, originally from Cornwall, is coping really well with the heat, despite some scorching on the very tip of its leaves. The fragrance is amazing, and so strong that even the air outside the polytunnel doors seems suspended in scent. By contrast, a new variety we’re trialling for the collection, which comes from Wales, has really struggled.

The runner beans are just starting to flower. Unfortunately, the heat has a negative impact on pollen quality, meaning that even when we manage to get into the tunnels to hand pollinate, the plants quite often drop the flowers because pollination has been unsuccessful.

Polytunnel pest watch 🔗

The intense heat has also led to a proliferation of pests. We’re starting to see spider mite on some plants – and we’re dealing with these by introducing predatory mites.

But the biggest pest issue by far has been aphids on the brassicas. There are some ladybirds in the polytunnels, but they’re not very keen on eating grey aphid. We have introduced parasitic wasps, but unfortunately soaring temperatures have meant that the aphids have multiplied quicker than the wasps!

One variety we’re particularly concerned about is (the perhaps ironically named) cabbage ‘Progress’. It has set seed but is currently being ravaged by an uncontrollable number of aphids, which are sucking the life out of the plant before the seed pods have fully developed and ripened. It would be heartbreaking for us to lose a variety at the last minute, especially one that has taken two years to reach this point.

However, we've managed to get most of our brassica populations over the line. This means they've flowered, set seed and the seed pods have reached harvest stage successfully.

With climate change bringing warmer summers for the foreseeable, we'll need to be thinking up new and inventive ways to manage this precious National Heritage Vegetable Collection.