Mary Keenan's Garden Diary: mind the gaps

My garden is always a work in progress and, apart from ongoing weeding, I am constantly tweaking the planted areas, removing plants that don’t perform well or that I tire of and adding plants that are intriguing. Right now, I am working my way through filling gaps in borders as the garden is in full growing mode and it is easy to see where additional plants are needed.

Filling flowerbeds and borders with plants is the best way to help keep them weed-free. The more plants that fill the space, the less chance there are for weeds to find a home.

Like the protection of an umbrella, maintaining a cover of plants also helps protect the soil from the effects of sun, wind and rain, reducing moisture loss, soil degradation and compaction.

Soil aeration and fertility

Soil aeration and fertility is also enhanced as decomposing plant debris provides organic matter and nutrients to the soil and, in turn, increases biological activity of earthworms and other forms of soil life.

When it comes to filling gaps, in some cases, it’s simply a matter of digging up a nearby perennial plant and dividing it to fill the space. In our larger garden, planting multiples of the same plant in drifts or en masse in a border gives greater impact and creates harmony.

I also like to repeat groupings of the same plant or a similar-looking plant or colour throughout borders for a more unified effect. While dividing perennials is best done in spring or autumn, with a little extra care, it is still possible to divide some but not all perennials now.

If you must divide plants at this time, it is a good idea to water the soil around any plants you will be dividing and their future home ideally the day before disturbing them.

Sturdy perennials

Sturdy perennials such as hostas, iris, hemerocallis, hardy geraniums, pulmonaria, phlox, nepeta and campanulas can still be divided now.

Before digging, cut the foliage back by half- this way a smaller root system won’t have to support lots of foliage in the summer heat.

When you have dug up and divided the plant, replant your divisions into their new positions quickly so the roots don’t dry out and water well.

Any plant that is divided in the heat of summer should be shaded from the sun for a week or so while they become established. You may also need to water daily for a few days after planting.

Of course, gaps in borders, are also a good excuse for buying new plants and, with tantalising stock in local garden centres and several plant fairs taking place around the country over the next few weeks, there is no shortage of sources.

Challenging

There are a few spots in my borders where it has proved quite challenging to successfully establish any plants, particularly where the soil is nutrient-poor, quite stony or sandy, and prone to drought in summer.

However, observing nature often gives clues as to what does well in particular growing conditions w- thistles are one group of plants that naturally thrive in these conditions. The ornamental plume thistle, Cirsium rivulare ‘Atropurpureum’ and several forms of sea holly or Eryngium have adapted well to fill gaps in these less hospitable soils, with deep root systems to access water that is a long way underground.

Keeping paths accessible is part of the tweaking process too and having allowed a long-established Viburnum davidii to extend a little too far over the border edge, blocking a path, it recently got a rather severe pruning. This is a small, mounded, evergreen shrub, with deep green, leathery leaves that are excellent for flower arranging.

Flattened heads of small, white flowers are produced in May followed by metallic blue-black berries in autumn. It is fairly low maintenance and needs little or no regular pruning, but will readily regenerate from old wood if cut back hard. All stems were cut back to around 30cm from the ground, cutting just above a dormant bud or to newly sprouting leaves.

This type of drastic pruning should be carried out ideally in late spring, so that the plant may put on plenty of regrowth before the following winter. It is a pruning method specifically for overgrown shrubs and should not be carried out as a norm. Mulch and feed after pruning to encourage healing and healthy regrowth. A less drastic alternative would be to hard prune one-third of the oldest stems over the next three seasons, resulting in a more natural-shaped plant over time.

Water lilies and other pond plants are vigorous growers and require division every three to four years. This is best done around now, and a warm, sunny day will make the job more pleasant.

Lift the plant out of the pond and remove the planting container. Use a sharp knife to cut the rootball into sections with two or three growth buds and plenty of roots.

Place the best pieces in special mesh-sided aquatic baskets, lined with hessian or other permeable material and fill with garden soil, just covering the crown and leaving the growing point showing. Add a 2cm top layer of gravel to hold the soil in place and return the plant to your pond.

Read more

Mary Keenan’s Garden Diary: break for the border

Mary Keenan’s Garden: it’s almost snowdrop season