Veronicastrum is one of those prairie flowers that has gained increased attention and popularity because of the emergence of prairie-style planting, the most significant development in planting style of recent decades.

Pursued originally in North America and Europe, “prairie planting” sought to emulate natural prairie grassland, using grasses and flower species that grew naturally along with grasses in wild native grasslands.

The results of this planting can be very beautiful, although it requires considerable expertise to choose the right combination of plants. It also requires much more maintenance than originally envisaged, especially on damp, weed-friendly Irish soil.

Elements of the style have been adapted in gardens, most notably a greater tendency to use grasses and an emphasis on a more natural appearance.

The style has also brought to prominence quite a few plants that were not much used previously, one of which is veronicastrum. This plant is a native of American prairie land and has the American common name of Culver’s root, though is more often known by its botanical name here. Culver is thought to have been a doctor who used veronicastrum as a herbal remedy for a variety of gastrointestinal ailments. The plant Veronicastrum virginicum has its native range from Canada to upland Texas, and with a range like that it can cope with any garden here. It is completely hardy.

Veronicastrum sends up tall stems in spring between 1.5 and two metres tall, so it is not for a small garden or restricted area, but it is ideal for a country garden with space to accommodate it. Whorls of three to seven narrow pointed leaves are spaced about 15cm apart up the stem. At the top of the stems are produced bolt-upright flowering stems, usually branched below the central main spike.

The flower stems are very slender and composed of hundreds of tiny tubular flowers. These open from the bottom of the spike producing filamentous stamens that give a slight bottle-brush look before fading to a lighter shade.

Although of delicate appearance, the flower spikes are very robust and, though upright, they retain a considerable degree of flexibility and can bend away from the wind. The narrow leaves and stems offer little resistance to wind, and their ability to sway brings an attractive movement to a border. They do not need staking.

Veronicastrum is in the same family as verbascum and foxglove, two other plants noted for their upright appearance and ability to give height and lift to a mixed border. The flower colour can vary, as the wild species can be pale purple, violet, pink or white. There are some named selections, such as ‘Fascination’ which is shown, purple-blue; ‘Lavendeltrum’, pale lilac; ‘Pink Glow’, pale pink; and ‘Adoration’, a deeper blue. There are white forms too. After flowering, the flower stems stay in place and wither to dark brown, and these last through winter, offering the upright accent alongside other good winter seed-heads. It looks great with grasses of any kind, especially the bigger grasses, such as golden oat grass, or miscanthus, or pampas grass, its flower colour enriching the grasses and, in winter, its withered stems contrast well with the strawy look of the grasses.

Veronicastrum is native to damp prairies and thrives in moist soil that drains but does not dry out in summer, so it is happy in heavy, damp ground.

It makes a neat clump, spreading outward relatively slowly and can be lifted and re-planted, or the clump reduced in situ and allowed to re-establish. Do not feed too much, as the plant just gets taller. CL

This week in the garden

Fruit, vegetables and herbs

Raspberry canes that have finished fruiting could be pruned out and the new canes tied into position. Summer pruning of vigorous apple trees could still be carried out to reduce vigour and increase cropping in future years. Remove apples or pears attacked by wasps to avoid even more damage. Pick herbs now.

Trees, shrubs and roses

Check young trees and shrubs for signs of drought. Shrub roses and ramblers could now be pruned by removing some of the shoots that flowered. Many established trees are showing early autumn colouring, which is strange, given the plentiful supplies of water, but there has been very good growth.

Flowers

Stay ahead of weeding in flower beds and borders. Prevent weeds from going to seed now. Take cuttings of tender plants such as marguerites, euryops, geraniums, fuchsias and African daisy to carry over winter, as soon as possible. Continue feeding baskets and other containers on a regular basis and watering too.

Greenhouse and house plants

Continue to train and side-shoot tomatoes and cucumbers. Take the top shoot off tomatoes to boost the green fruit that is already present. Tidy up all kinds of plant debris and be careful not to overwater, or to splash water about. From now on, grey mould disease becomes a problem for many greenhouse plants.

Lawn

With the rain and sunshine, most lawns have done quite well this summer, but some are showing signs of a moisture deficit and have dried up a good deal, with growth much reduced, especially on light, free-draining ground. Do not use any fertiliser or lawn weedkiller when a lawn is in that condition.

Silver leaf disease

Silver leaf disease is a very common problem with plum trees, especially the most popular, and best, plum variety, ‘Victoria’, which suffers badly from this disease, usually killing the tree progressively over a period of years.

The disease is caused by a fungus that usually gets in through branch breaks and pruning cuts. It blocks the tree’s water vessels and causes silvering of leaves on affected branches, usually one branch being affected first. Silvering is easiest to see now and affected branches should be cut back beyond some green leaves.