They can also grow beyond their allotted space and need to be divided. The new ageratum 'Blue Horizon' is a tall version of the shade loving dwarf blue. It forms a wonderful partnership with yellow day lilies. It can also be planted amongst a grouping of white perennials to offer a season-long blue contrast to the seasonal whites such as Candytuft, Baby's Breath, White Lilies or White Foxglove. The sweet potato vine will twine its way delicately through Artemisia to add an extra splash to an over-abundance of grey foliage.
Nasturtiums are always an excellent addition for the edges of beds or pathways.
They will gradually spill over the defined edges and give a natural appeal to the garden. They can also be extremely prolific producers of edible flowers and pepper flavoured flower buds. Summer flowering bulbs, or those which need to be overwintered indoors, are other excellent companions in the perennial garden. Whether these are placed outdoors in pots and allowed to mingle with the foliage of other plants or planted in the soil, they will add some surprising and unique attributes to the garden. Dahlias are almost too good to be true when you see a well grown specimen.