· by Michael Blair, Nashville's Landscapers
Almost every planting-against-the-house problem starts with sizing the gap to the plant that went in rather than the plant it will become. The nursery tag lists a mature width. Half of that, plus a working gap for the wall, is the minimum distance from the foundation, and for most shrubs that is far further out than people are comfortable planting.
Start from mature width, not pot size
A shrub that reaches six feet wide needs its center three feet from the wall just to avoid touching it, and it needs to avoid more than touching. Foliage pressed against siding holds moisture, blocks the wall from drying after rain, and gives insects a bridge onto the house. Add at least a couple of feet of working space beyond the mature radius so there is room to walk behind it.
That space matters more than it seems. Termite inspectors, painters, pressure washers, anyone servicing a hose bib or crawl space vent all need to reach the foundation. Plantings that block it get cut back hard or removed later, and the plant rarely recovers its shape.
Trees are a different calculation
Tree roots spread well beyond the canopy, and the question with a tree is not the trunk touching the house but roots and limbs. A small ornamental such as a dogwood or a redbud can sit fifteen feet or so from the foundation. A shade tree, an oak, a maple, a tulip poplar, wants to be far enough away that its mature canopy clears the roof and its roots are not working under the footing.
In our clay soil there is a second reason for distance. A large tree draws a great deal of water from the ground in a dry August, and clay shrinks as it dries. A big tree close to a foundation dries the soil unevenly under it, and that differential movement is a known cause of cracking here. The same tree thirty feet out is simply a shade tree.
Grade, water and the crawl space
Whatever goes in, the ground should still fall away from the house afterward. Beds built up against the foundation to hold mulch and plants routinely reverse that grade, and then every rain is directed at the crawl space or basement wall. Keep bed soil below the top of the foundation and below any siding, and keep the slope.
Mulch should stop short of the wall by a few inches and should never be piled against siding or brick. A mulch bed touching the house is a moisture reservoir and a runway for termites and ants straight to the wood. Bare or gravel-covered ground at the wall itself is the correct detail, even if it looks unfinished for a season.
- Ground slopes away from the house after planting, not toward it
- Bed soil stays below siding and the top of the foundation
- Mulch stops a few inches short of the wall
- Irrigation heads and drip do not wet the foundation
Choosing plants that fit the gap you have
The honest answer for a narrow bed, three feet or less, is a narrow plant. Dwarf and columnar varieties exist for most common foundation shrubs and they keep their size without endless pruning. The alternative, planting a large variety and shearing it into a box every year, produces a dense outer shell and a dead, hollow interior.
Plant lists for Nashville clay are their own subject, but for the space immediately against a house the priorities are mature size, tolerance of the reflected heat off a south or west wall, and a root system that stays in the bed. Get those three right and the plantings will still look intentional in fifteen years.