The sea holly that most people are familiar with is the one that stuck its spines in their foot or hand when they were a child by the seaside. The wild sea holly is a native plant, found growing on beaches around the country.

While it is widespread, it is not found at every beach but can be quite common when it is. The whole plant is spiny with a coating of grey-blue wax. The flowers are blue-tinged mounds of tiny florets. The name sea holly comes from the very similarly-shaped leaves and bracts just under the flower heads.

These are about the size of holly leaves and have spines arranged in the same pattern around the edge. The plants are usually found just at the head of the beach where the sand is fairly stable. When covered by wind-blown sand or tide-driven gravel, sea holly has a remarkable ability to push its way to the surface and resume growing.

Wild sea holly has not been grown in gardens, probably as it’s too spiny, and it is possible that this aversion has gone against the other species too. However, they generally appear in the gardens of keen gardeners, and they make great contrast with most flowers, especially yellow and orange ones. The flower heads are unlike those of any other plant. Although they look like members of the thistle family, they are actually part of the carrot family, which usually make flat umbels of small flowers, such as those of cow parsley or hog-weed.

In this case, the tiny blue or white flowers are held in rounded or domed structures. Just under the flower head is a ruff of bracts. These are like holly leaves in the sea holly and variously much divided in other species. Each leaf division carries a sharp spine, some of them rather soft. Sea holly and its many related species in the genus eryngium are mainly plants of dry soil and the development of the sharp spines is a defence against grazing animals, hungry for fodder on dry land.

One of the most popular eryngiums is Eryngium alpinum, which has rounded spiny leaves at ground level and these get more spiky as the flower stem is pushed up, forming a remarkably frilled, spiny ruff. This one grows to about 70cm tall and stands stiffly upright, as most kinds do, unlike the wild sea holly which tends to flop about a bit.

A succession of blue flowers appears on the plant starting in July and continuing to late summer. The first flush of flowers is best but the follow-on is useful. Eryngium giganteum is commonly called Miss Willmott’s ghost, because a lady of that name was believed to have been in the habit of sprinkling seeds of this flower surreptitiously into borders in gardens she visited. Above one metre tall, it is a relatively short-lived perennial.

Eryngium alpinum is originally from the European mountain ranges and, it being so showy, has been used in numerous crosses to give garden forms. Eryngium x oliverianum is one such example, tall to 90cm, with large blue, sometimes purple-blue, spiny ruffs, somewhat less divided than the parent. Another of its hybrids is the very pretty Eryngium x zabelii, also very well furnished with bracts and available in blue and whitish forms.

Eryngium bourgatii is from the Pyrenees, shorter than the others and with fewer, smaller, spiny bracts held in a star-shape. There are many other kinds, including the two-metre Eryngium pandanifolium from South America, which, unlike those mentioned, is hardy only in mild areas. All kinds like really well-drained soil, a bit more moist for the big kinds.

Cleavers upsurge

The weed known as cleavers, which also has the common names of goosegrass and sticky nellie, seems to be having an exceptionally good year. For some reason, it is far more plentiful in gardens this summer. Perhaps the mixed spring weather or the good long summer last year have favoured it as it is all over gardens. It has long straggly stems with starry whorls of small narrow leaves. These have tiny hooks that point back towards the ground and these hold the stems in place as they clamber over flowers and shrubs.

If there are enough stems, this weed can shut out the light from a support plant and cause loss of foliage. Cleavers is easily pulled off plants in handfuls and pulled out or hoed out at ground level. Try to do this while the large round seeds, about the size of wheat grain, are immature as this prevents viable seeds from being returned to the soil to cause problems next year.

Fruit, veg and herbs

Humid and showery weather is conducive to potato blight, affecting potato and tomato plants. Make late sowings of spinach, lettuce and radishes. If the soil is dry, peas, broccoli, sweet corn and cabbage should be watered to keep the plants growing. Pick all kinds of vegetables while young and tasty.

Flowers

Cut down the flower spikes of lupins and delphiniums that have flowered and they might give some later flowers. Pots and containers of all kinds will need frequent watering, even every day, if the weather is hot and dry. Feeding increases the amount of watering needed but it is worth the effort.

Lawns

The recent dry spell has tested lawns on sandy ground and in places where there is not a great depth of soil. Mow less often, raising the blades, and do not feed until there is plenty of rain and the soil is moist. Try to avoid unnecessary wear and tear on the grass, but do not water, it will recover after rain.

Trees, shrubs and roses

Check to make sure that young trees are not dry and struggling. Water heavily if necessary. It is time to clip hedges of all kinds before the wood gets tough. Any heavy cutting back should be left until the start of the growing season next year. Roses may need spraying if there are long spells of rain.

Greenhouse and house plants

Take cuttings of many kinds of shrubs and tender plants to raise new plants. Continue watering and feeding greenhouse plants. Be careful to water tomato plants in pots or grow-bags regularly. These can easily dry out and cause blossom-end rot. Train and side-shoot tomatoes and cucumbers.