The yellow flag iris is a wild, native species of iris often seen growing in wet low-lying land, or typically the poorly-drained bottoms of fields. It is one of only two native species of iris, the other being the stinking iris, an evergreen native of woodlands in milder areas. The flag iris is a tall plant, ranging from 75cm to 1.5m. Grown as a single plant, it usually remains on the smaller size, but when it forms a large thicket of foliage and stems the plants can force each other upwards.

It begins to flower in late May or early June, with large, bright yellow flowers of typical iris shape – three upright petals and three petals hanging down. The lower petals are rounded and much broader than the upright ones. These lower ones have a ring of small purple markings which lead to the centre of the flower and offer a guide to visiting pollinators. Each flower opens at the top of the tall flower stem and the flowers open in sequence, which prolongs the flowering period. Some plants can still be flowering in August, though most finish earlier.

Over recent decades, some of the wet areas where yellow flag thrives naturally have been drained and the iris is not as widespread as it used to be. But there is still plenty of it about. It is not grazed by livestock because it is poisonous. All parts have glycosides that are very bitter and animals avoid the plant. Heavy trampling of wet ground by livestock can reduce the number of plants, but it is a tough survivor. The tannin-rich root rhizomes have been used in herbal medicine for a variety of ailments, including rheumatic conditions.

With increased interest in natural gardening and especially in gardening for wildlife, as well as the creation of wildlife areas under GLAS, there is likely to be greater planting of wild native species, including the iris. The number of native species grown in gardens is limited, but the flag iris is one of them. Most garden species have larger flowers than wild species, or are more prolific in flowering, but the iris is as good as most highly-bred garden cultivars. There are some garden forms of the wild plant that have been selected.

Alba has flowers of pale yellow, while Golden Fleece has deeper yellow flowers than the type species. The most widely grown form of the flag iris is Iris pseudacorus or Variegata, which has white or pale yellow-striped leaves. These are slender and upright like those of the species itself, but they do not grow as tall. The striped kind can look very lively in spring, as the new leaves push up rapidly. But it does not flower so well, having less green chlorophyll in the leaves. The flag iris is a water iris and can grow happily in shallow water as well as in wet ground. While it can tolerate dry soil for a while, it eventually fades out on well-drained soil, which is why it is not seen wild, except in wet places. It does well as a marginal plant growing by the edge of a pond. It can spread by means of its rhizomes and by seeds, which are produced in fat pods. These dry out in autumn or early winter and split to release the seeds, which can be distributed by water. To prevent seeding, the flower stems are easily snipped off after flowering, and the rhizomes are easy to keep restricted to a chosen area. Although it might not appeal to all, the yellow flag iris has a wonderful, natural simplicity that only native plants offer. CL

Beech aphid

It looks like the beech aphid will not be as big a problem this summer as it has been in some recent years. The beech aphid is a form of greenfly that attacks beech trees, especially young trees and hedges. The aphids have a woolly coating that helps to ward off predators. The aphids feed on the underside of the leaves, causing deformation and, in a heavy attack, reducing plant growth drastically.

Young trees can be set back so severely that they may die off or die back in winter. The dust from the aphids makes hedge-trimming very unpleasant and unhealthy to inhale.

Watch for the presence of aphids and if the numbers build up to the point where most leaves are affected and natural predators are overwhelmed, you may need to spray with a garden insecticide.

>> This week

Trees, shrubs and roses

Check young trees and shrubs for signs of drought, as young plants can suffer badly in early summer. Continue to spray roses against blackspot disease, especially in the damper parts of the country, if blackspot is a problem. Continue to tie in the new shoots of climbing roses.

Fruit, vegetables and herbs

Thin out vegetables that have reached suitable size and control weeds early. Sow Savoy cabbage, winter cabbage, cauliflower, purple sprouting broccoli and swede turnips. Tender vegetables, such as sweetcorn, outdoor tomatoes, pumpkins and runner beans can be planted out.

Flowers

Bedding plants can be planted out and containers and baskets planted up. Unless slow-release fertiliser is used, potting compost runs low on nutrients. Be sure to control the first flush of weeds among bedding plants. Continue to watch for slugs and snails in the first few weeks after planting.

Lawns

Grass growth has been generally quite good despite the cold spell and dry weather. The weather has been dry for applying lawn fertilisers or lawn weedkiller, and if either of these needs to be done it is best to wait for a settled spell of good growth after rain for good results.

Greenhouse and house plants

Tomato, chilli peppers, cucumber and sweet pepper can still be planted in a greenhouse, but do not delay further. Continue to feed greenhouse plants every two weeks to get good growth before mid-summer and continue to water well. Pot up house plants that need it.