Most outside maintenance comes down to keeping water moving somewhere useful. At the foot of a wall that stops being a tidy principle and starts to matter, because it is the only place where the garden and the inside floor sit a few courses of brick apart.
Find the barrier before you do anything
Look along the brickwork roughly a hand's width above the soil for a thin dark line running through one mortar joint, or a band of slate on anything built before the war. That line is the barrier holding ground moisture out of the wall above. Below it, the brick is meant to be wet. Above it, dry. The entire arrangement rests on one condition: the outside ground must stay lower than the line.
What defeats it is rarely dramatic. A border gets a barrow of compost every spring. A path is laid on top of the tired one rather than lifted and replaced. Gravel goes down around a bed to stop the weeds. Two or three inches gained over a decade will bury that barrier, and a buried barrier is simply bypassed, with moisture travelling up into plaster that was never meant to receive it.
If it has already come inside
Prevention and aftermath are separate jobs. Skirtings that have swollen, a carpet wet along one edge, a smell in a room that has been shut up for a week: at that point the question is no longer the garden, it is drying the fabric of the building out properly and in the right order. For readers in the States writing in about exactly that, a firm handling flood damage cleanup in Dallas sets out the sequence sensibly, and the order genuinely matters more than the equipment does.
Airbricks have to breathe
A suspended timber floor stays sound because air crosses underneath it. Those small vents at low level are the whole ventilation system for that void, and they are easy to lose: buried by a raised bed, rendered across during a repair, painted shut, or blocked by a new patio laid at the wrong height. Count yours and clear them. If one is below the finished ground level now, it wants a periscope vent rather than a shrug, because a sealed void under a wooden floor is how joist ends rot out of sight.
Render, paths and the small details
Render carried down over the barrier and onto the footing gives water a bridge across it, which is why a neat skirt of render at the base of a wall often sits above the dampest plaster indoors. Cut it back and leave the joint open.
Paths want a fall away from the house of about one in eighty, and a gap of ten or fifteen millimetres against the wall rather than mortar packed tight into the joint.
When to stop
Plaster blown in a band above the skirting, a tide mark that returns after decorating, or any smell of must in a room with a timber floor are all past routine work. Those want investigating before anything is replastered, because replastering a wall whose ground level is wrong simply hides the evidence for a season.