Evening primrose

Evening primrose will grow in any soil and likes full sun. Two species are naturalised in Britain, so it’s easy to find free seed. Photograph: Alamy

The summers of my childhood seemed to be full of moths. Masses rose up from meadows; nights were full of them bouncing at the windows – they were everywhere. And now they are not.

Butterfly Conservation’s recent news that we are seeing a significant population fall since the 1970s is a chilling wakeup call. Moths are a key part of the food chain; they pollinate night-scented plants. Their decline indicates a wider issue about insect biodiversity and agriculture. Your back garden won’t save the moth population, but it may act as a haven while we get our act together.

There are thousands of British moths, both day- and night-flying, and their food sources are as varied as the group. However, here are two easy biennials to sow now that look wonderful, and which will be enjoyed by many moths on a warm night.

Sweet rocket (Hesperis matronalis) and evening primrose (Oenothera biennis) grow leaves one year, then grow tall and flower in spring. Once they set seed, they often die.

Sow from now till July; they’ll germinate easily. To try to control where they go, scatter them on bare ground or sow them in a pot. Both self-seed readily: if you let every plant go to seed, you may have a lot of weeding to do next spring.

Sweet or dame’s rocket is a member of the cabbage family and has lovely lilac or white flowers that smell divine in the evening. It grows 100cm tall and branches, so is best towards the back of a border. If you forget to deadhead it, and it spreads its seeds everywhere, you can eat the young leaves if you are desperate for a salad before it flowers. Or wait and collect the seeds: this is a little fiddly, but they are rich in good oil and can be used in a seed mix with sunflowers and sesame. It works well in darker places, where the white flowers bounce light around late into the evening.

Evening primrose (left) is taller yet, growing to 150cm. It has long taproots, so it’s not easy to weed out once established. Late in the evening, the pale sulphur-yellow flowers are covered in moths. In the early morning, you’ll find bees foraging for pollen. Evening primrose will grow in any soil and likes full sun. Two species are naturalised in Britain – Oenothera biennis and O. glazioviana – making it easy to find a source of free seed. It’s not easy to tell them apart, particularly as they hybridise, but O. glazioviana has larger flowers and more reddish sepals.

The roots of O. biennis are edible before the plant flowers, though they must be cooked – treat them much like salsify. Again, you can collect the seed to eat.