RHS Journals
The Garden
May 2007
Going under the knife
Revitalising an over-mature border is daunting, but it can allow a new range of plants to be grown, and could make your garden better than ever. Phil Clayton cuts through the undergrowth.
Images: Tim Sandall
Rather as with people, gardens pass different stages as they age. Each stage has its own feel - personality, even - and each its merits, but as time passes by, gradual changes mean we must make adjustments. After the exciting, heady days of planting and establishment, a border will fill out and mature. It depends of course what and how you plant as to how quickly this happens.
Some plants grow rapidly, such as sun-loving Cistus: these are at their best after three to five years; others take longer to develop their full potential. Cornus controversa ‘Variegata’ (wedding cake tree) doesn't start to display its spectacular layered pattern of branches until 10 years from planting.
Most gardeners therefore choose a mixture of plants, some growing quicker than others. With regular upkeep, these plantings thrive for perhaps seven to 10 years but then, without remedial action, they begin to look tired; shrubs become bare at the base and outperform plants growing below.
Rejuvenating a mixed border
Thinning out and underplanting existing shrubs is best carried out in spring or autumn.
An overgrown border may initially appear hard to tackle; try first to identify the main problems. The shrubs are overgrown, shading
out herbaceous planting that is now unsuitable for the site. The soil needs cultivating, weeds and rubbish clearing away.
Raising tree and shrub canopies will allow light and rain to reach the ground, enabling later underplanting. Remove the lowest branches, and cut out any badly placed, dead or diseased stems. Take out any shrubs that are too old or misshapen.
Reducing competition at root level is important when improving the soil. Do not be afraid to cut out a few roots to help loosen the soil. Remove any weeds and rubbish, dig in well-rotted manure or garden compost, breaking up any large, hard clods of soil.
The cleared and prepared site will be lighter at ground level, the soil ready for planting. Overhead canopies have been thinned and good existing specimens such as the central hibiscus given more space.
Position underplanting before planting. Include a mixture of plants to provide interest at different times of the
year; some existing perennials
can also be split and reused if
they are still suitable.
The rejuvenated border now has a good overall effect. The new planting needs watering in to ensure rapid establishment. Mulching the soil provides the final good looks and helps keep weeds down.
The march of time
Few people consider how conditions in a garden alter as time passes. Sunny borders soon become shaded as shrubs and trees grow up, reducing light levels, while once-moist, friable soil becomes thick with roots, sucking up moisture. Distinct layers of growth develop, one with tree and shrub canopies, another beneath with smaller shrubs and taller herbaceous growth, and a third, perhaps at just above ground level, where there is least light. This pattern roughly mimics conditions in wild woodlands. Plants that used to thrive in the sun no longer survive, or fail to perform as they once did, having been outcompeted by better-adapted and, by now, taller bedfellows.
The garden can now look tatty; many people are tempted to rip out the lot and start again. This is a waste, for these changes should be used by gardeners to their advantage. Despite its overgrown nature, the site will be sheltered from winds and have a more constant microclimate, and while competition may have seen off prized plants, the same will have happened to weeds that once caused problems. This is the time to capitalise on these virtues, taking the garden forward to the next stage in its evolution.
Remedying the problem
There will now be plenty of interest at head height and above; problems are likely to be below the tree and shrub canopies, which may now be dense and knitted together. Some plants are best removed, perhaps a woody Buddleja or Hypericum: they may have been planted too close together, or may now be unsightly. Others will be fine specimens deserving more space around them.
Many trees benefit from having lower branches removed, which improves their appearance and allows light and air to plantings below. Shrubs, too, can be ‘legged up’, their lower branches (which are often tatty and containing much dead wood) removed. Others with a multistemmed habit, such as Philadelphus or Kerria, may be a tangled thicket and can be thinned, encouraging shoots from the base. This results in more light and moisture reaching the ground.
Any surviving herbaceous plants will probably need attention. Some will need repositioning, others splitting and replanting. This will mean improving the soil. If the ground has been regularly mulched, it is likely to be in good condition, but it may be full of roots, especially close to the shrubs. Loosen the soil and don't be afraid to cut away some root growth, as long as it is not too close to the main stem, and incorporate well-rotted manure or garden compost.
With these improvements in place, replanting becomes possible. While some plants from when the garden was young will no longer thrive, conditions allow a new range of plants to flourish, plants giving the garden a more sophisticated feel now that it has reached middle age. The soil, especially if it has been regularly mulched, is likely to be rich in organic matter and of a lower pH, even on alkaline soils; below sheltering shrub canopies, relative humidity is higher which is ideal for woodland plants.
Planting for the future
Phil Clayton is Features Development Editor for The Garden
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