There are a few basic principles to keep in mind. I will spare you the details but be sure to think about these 5 aspects:

1. Size
2. Colour and Interest
3. Purpose
4. Maintenance
5. Cost

Combinations

There is no one answer for everyone as you will all have different needs. Here are a few combinations I enjoy, many of which I have in my garden:

Echinacea and Miscanthus: growing along my driveway. The bold purple flowers contrast the dark green grasses and the height provides privacy where it’s needed. Bonus: a lot of winter interest here and great for attracting birds.

Artemisia schmidtiana and lupin: the soft, silvery foliage of the artemisia contrasts the tall vibrant colour of the lupin.

Bergamot, Hosta, and Rudbeckia ‘Autumn Sun’: growing in front of the house. Provides varying heights and complementing yellows and reds plus the hosta does well in the shade of the taller perennials.

Clematis and boxwood: the boxwood can provide a barrier, some privacy, or interest and the colourful clematis blooms will really draw the eye if placed to climb behind it.

Hydrangea and Rudbeckia ‘hirta’: growing alongside the barn. Unlike ‘Autumn Sun’, ‘hirta’ grows to a shorter height so as not to overshadow the hydrangea but still provides excellent shape and colour contrast.

Milkweed, Echinacea, and Buddleia: the ultimate butterfly attractor.

Add non-plant interest to your garden if you have the space: bird feeders, benches, rocks, and wooden stumps provide a resting place for you, the birds, and any other wildlife that stops by.

Finally, don’t expect perfection over night; perennial gardens take time to fill in. I’ve been growing mine for 8 years now and it’s still a work in progress!