A bank that faces the sun all day, bakes dry by July and refuses to be mown is one of the most awkward corners of any garden. Turf thins, bare soil shows through, and every spring the weeds move in. Spreading junipers are among the few plants that will take that ground on and keep it, year after year, without asking much in return.
They are not instant, and they are not right for every slope. But on sunny, free-draining ground they are hard to beat.
Junipers in the prostrate group — Juniperus horizontalis, Juniperus procumbens and the low forms of Juniperus squamata and Juniperus communis — grow outwards rather than upwards. Stems run along the surface of the soil, and where they touch, they root. Over a few seasons you get a dense, springy mat that does three jobs at once.
Add wind tolerance, a tolerance for stony, hungry soil and a real dislike of being fussed over, and you have a plant that suits a bank better than most. What junipers cannot stand is wet feet.
There is also a seasonal argument for them. Most prostrate junipers hold their colour through winter, often taking on plum, bronze or steel-blue tones when the temperature drops. On a slope that might otherwise be a smear of dead grass and mud from November to March, that matters. The same dense mat also shelters ground beetles, spiders and other small predators that help keep pest numbers down in the rest of the garden.
What junipers are not is a quick fix. A flat of nine-centimetre pots planted in spring will still look like a collection of green starfish by autumn. The reward comes in year three and four, when the stems meet, root and close ranks.
Match the plant to the space using its mature spread, not the size of the pot on the bench. A few reliable options:
If you garden in a cold pocket, check the hardiness rating before you buy. Most of these are hardy to at least USDA zone 4 or 5, but Juniperus procumbens is less reliable in very exposed, freezing sites. In hot, humid summers, good air movement around the foliage is more important than rich soil.
Plant junipers high, not deep. The root flare — where the trunk meets the roots — should sit level with the soil surface, never buried. A buried flare is the quickest way to lose a juniper in its first year.
Before you buy a single plant, spend a few minutes on drainage. Dig a hole about 30 cm deep and fill it with water. If it drains within an hour, you have the free-draining ground junipers want. If it is still full the next morning, choose something else. Junipers will not forgive a wet root zone, especially in winter.
Clear perennial weeds first. Bindweed, ground elder, brambles and tough grasses will push through a young juniper mat and are far harder to remove later. On a steep bank, smothering with cardboard weighted by gravel for a season can weaken them without spraying. If the slope is very steep, cut shallow terraces or planting pockets into the face so each juniper has a level spot to sit in. This also slows runoff and gives the roots a chance to establish.
Junipers do not need rich soil. In fact, too much compost or fertilizer encourages soft, floppy growth that is more likely to suffer in wind and cold. On thin, stony ground, plant straight into the existing soil. On heavy clay, improve only the planting pocket with coarse grit and a little well-rotted organic matter, and keep the surface around the plant mulched with gravel rather than rich compost.
Space plants according to their mature spread. As a rule, set them so that their centres are about half the mature spread apart. A juniper that will eventually reach 2 m across can be planted 1–1.2 m from its neighbour. On a slope, stagger the rows rather than lining them up like soldiers. The mat will close faster and look more natural.
Water new plants once a week during their first summer and in dry spells through the second. After that, they should be independent. If you are planting in autumn, the rain may do the work for you, but check during any mild, dry spells.
Once a juniper bank is established, the main task is restraint. Do not feed it. Do not water it unless the soil is dry well below the surface. Do not shear it into tight cushions. Junipers grow from the tips of their stems, and most will not regrow from old, bare wood. If you cut a branch back into the brown centre of the plant, you are left with a permanent hole.
Light pruning is still useful. In late winter or early spring, trim back any wayward stems that are spilling over a path or smothering a neighbouring plant. Take off only the green tips, and do it with secateurs rather than hedge shears so you can see what you are cutting. Remove dead or broken branches at any time.
Weed control is easiest in the first two years, before the mat closes. Hand-pull annual weeds and spot-treat perennial thistles or docks with a careful dab of weedkiller on the leaves, shielding the juniper with a piece of card. Once the canopy is dense, few weeds get through. Gravel mulch around the edges will stop grass creeping in from the lawn.
Watch for juniper blight in wet, humid weather, which causes dieback of shoots and brown patches. Prune out infected branches in dry conditions and improve airflow. Spider mites can be a problem in hot, dusty sites; a strong jet of water over the foliage in the evening helps, and predatory mites usually catch up. Bagworms, where they occur, are best picked off by hand in winter when the cases are easy to see.
Junipers fail in shade. A north-facing bank under trees, or any slope that stays damp, will leave you with thin, leggy plants and patches of bare soil. They also dislike heavy, poorly drained clay that sits wet all winter. In those places, look instead to creeping cotoneaster, bearberry, ivy or ferns for shade, and to Siberian iris, dogwood or willow for wet ground. On a hot, dry slope in a wildfire-prone area, keep junipers away from the immediate zone around buildings; their resinous foliage burns readily. Gravel mulch and low herbaceous groundcovers may be a safer choice there.
Imagine a bank 6 m long and 2.5 m deep, facing south, with thin soil and full sun. Using Juniperus horizontalis 'Wiltonii', which spreads about 2 m, plant in two staggered rows. Put the first row 45 cm from the top edge and the second row 1.5 m below it, with plants 1 m apart within each row. That is roughly twelve plants. Add three Juniperus squamata 'Blue Star' near the top for contrast, and mulch the whole area with 5 cm of gravel. Water weekly for the first summer, then only in drought. By the third year, the blue rug stems should be touching; by the fifth, the bank should be a continuous mat that
Photo: Andy_Bay / Pixabay
