Terrace box planting

[flowerpower32]

Despite my name I know nothing about gardening. We have recently had an extension plus a quite involved decking area (our house is about 6 feet above the garden level). We have built in benches in a large L shape and all around the top (above seated head height) are planters. There is about 5 meters in total and the boxes are relatively shallow. The extension is quite smart / modern (a bit mini grand designs-y) and these planters are very visable both from the house and garden so feeling the pressure to get this right! Any advice on what to go for would be very appreciated. It needs to be low maintainence and look good year round. I also want to be able to just stick in stuff and leave it for years. Thinking maybe grasses interspersed with heather and something else so give colour when that has gone over? Maybe barking up wrong tree though! Envisage maybe three plant types planted in sequence? Thank you in advance.

[flowerpower32]

Brilliant advice and love all of those suggestions! Thank you. They are probably about 30cm deep, 20cm deep and 5 meters long. Love the idea of lavender. Wonder if alliums may be a bit high but something that does come up a bit higher would be good. Yes, will be in full sun.

[TheRhythmlessMan]

How big is the planting area of the planters? Are they in full sun?

Grasses and heather sound like a lovely idea!

Lavender would smell delicious and looks effective en masse.

Maybe you could mix in some architectural plants like alliums. That'd look nice with grasses too. The seed heads of Allium Christophii look amazing after flowering too and last most of the season in my garden.

Have you considered trailing plants hanging over the edge, like ones you find in hanging baskets?