Wall and Foundation Planting Plan

Two things make a wall bed different from the border ten feet away, and neither is obvious until something dies.

The first is water. A wall casts a rain shadow, and the strip at its foot receives a fraction of the rainfall the open garden gets, because prevailing rain arrives at an angle and the wall intercepts it. On the sheltered side, a bed can stay dry through a week of rain.

The second is that a wall is not a barrier. Browsing runs from the ground to roughly six feet, and a deer standing on the far side of a four-foot wall reaches everything on top of it and most of what is behind.

What a wall actually does to the site

Rain shadow. Worst in the first 12 to 18 inches, and it does not go away in a wet summer.

Reflected heat. A south or west-facing wall radiates into the evening. The bed runs several degrees warmer, which extends the season at both ends and dries the soil faster.

Rubble and poor soil. Builders backfill foundations with whatever came out of the trench. Wall beds are frequently half brick and mortar, high in lime from the mortar itself, and shallow.

Frost pockets and drips. A wall with no gutter above it delivers a concentrated line of water in one place and nothing either side.

Aspect does more here than anywhere else in the garden. The same eight-foot bed is four different sites depending on which way it faces.

The plan, by aspect

Bed depth of at least 3 feet, and preferably 4. A narrow strip against a wall is the driest, hottest, most root-restricted ground you can make, and it is why 18-inch borders under walls fail so reliably.

Set the first row of plants 12 to 18 inches out from the face, clear of the worst of the rain shadow and clear of the footing.

South or west facing. The Mediterranean case, and the easiest.

Every plant there is Rarely Damaged and every one of them wants exactly what a hot dry wall base offers. This is the one situation where the difficult site and the resistant palette want the same thing.

North or east facing. Cool, shaded, often damp at the base and dry higher up.

Ferns are the strongest choice available in shade: every fern on the Rutgers list sits in the top tier, and that is the only plant group on it that is unanimous.

Both aspects, through the whole bed: 20 or more daffodils. Never tulips against a wall, where deer can reach them from two sides.

Climbers, and the reach problem

The instinct with a wall is to cover it, and this is where the six-foot browse line bites.

Anything trained on a wall is eaten from the ground to six feet, which on most garden walls is all of it. Clematis and climbing hydrangea are both rated Occasionally Severely Damaged, meaning Rutgers' own guidance is that they need fencing or repellents.

Three ways through it:

• Grow the climber where the base is protected by the planting in front of it, and accept that the first two feet may be chewed. Established woody climbers survive that; new ones often do not.
• Choose a climber that carries the flowering above six feet and treat the lower stems as plumbing rather than display.
• Protect the first three growing seasons with a cage or mesh sleeve, then stop. The plant only needs defending until it has enough mature wood to lose some.

A wall shelters a climber from wind and cold, which is a real advantage, and it does nothing whatsoever about deer.

Getting it to establish

The rain shadow is what kills wall plantings, and it kills them slowly enough that people blame the plants.

• Water deeply and infrequently through the first two seasons, at the base of each plant rather than over the bed. Overhead water lands on foliage and evaporates off a warm wall.
• Improve the whole bed, not the planting hole. A rich hole in poor rubble becomes a sump in winter and a pot in summer.
• Check for builder's rubble before planting. If the top spit is half mortar, remove it rather than plant into it.
• Mulch, but keep it off stems. Grit rather than bark on the sunny aspect, which suits the plants and does not hold damp against the wall.
• Fix the gutter first if there is one, and site nothing valuable under a known drip line.

What to skip

• Hostas and daylilies on a shaded wall. It is the obvious planting and it is a feeding station.
• Tulips, anywhere near a wall.
• Anything that wants even moisture in the first 18 inches of a rain shadow.
• Boxwood right against the face, where restricted air movement encourages blight in humid regions. A foot of clearance changes it.
• Self-clinging climbers on soft mortar. A deer problem this is not, but it is the other way people regret a wall planting.

Upkeep

• Spring: check the base of climbers for winter browsing before assuming dieback is cold damage. Torn, shredded stubs are deer; clean angled cuts are rabbits.
• June: shear lavender and thyme lightly after flowering, never into old wood.
• Late winter: cut back russian sage hard, to about 12 inches.
• Any dry spell over two weeks in the first two years: water, even if the rest of the garden is coping. The wall bed is not seeing the same rain.

The ratings above are Rutgers practitioner consensus from northern New Jersey rather than a controlled trial, and the publication notes that no plant is deer proof and that results depend on local populations and weather. Rain shadow severity depends on wall height, prevailing wind and roof overhang, so treat the 12 to 18 inch figure as the zone to plant outside of rather than a measurement of your own wall.