A border that peaks in June and collapses in September is not a plan, it is a good weekend at a nursery. The test we set ourselves is what the garden looks like from a kitchen window on a grey afternoon in the middle of February.
Structure first, flowers second
Before anything flowering goes on the plan, we place the evergreen bones: clipped box, yew, pittosporum, a few well-sited shrubs. Perhaps a third of the planting by area. That is what carries the border through the months when nothing is in flower.
Get this proportion wrong and no amount of summer colour rescues it.
Leave the grasses and seedheads standing
Cutting everything back in October is a habit, not a rule. Calamagrostis, miscanthus, sedum heads and echinacea cones hold their shape through frost and give a border something to do all winter. We cut back in late February, just before the new growth starts.
It is also better for the insects overwintering in the stems, which is a reasonable secondary argument.
Repeat a small number of plants rather than collecting many
A border reads as deliberate when the same five or six plants recur along its length. Twenty different things in twenty ones and twos reads as a collection, and it never quite settles.
This is the single change that most improves an existing border, and it usually means moving what is already there rather than buying anything.
