Planting scheme for under stepover espalier apple trees

Hi
I have a narrow, long bed, approx 7m long and 30cm wide, which separates my flower garden from my veg plot. I planted stepover espalier apple trees last autumn to act as a low divider and want to add some planting underneath. This will need to be low so it doesn't detract from, or get in the way of, the apple trees. I like the idea of having some colour after the apple blossom is over and before the fruit (which I realise may not be for at least a couple of years!)
I am in southern Cumbria so get a lot of rain and cold weather in winter. The garden is east facing and gets lots of sun when it is out. The bed was completely dug out before planting and the soil replaced with a good mix of good topsoil and compost. The rest of the flower side of the garden was planterd up last summer and is a mix of shrubs and perennials with lots of colour and interest through the year with lots of plants that are good for pollinators.
Photos attached. Any suggestions would be very welcome Thanks



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My first thoughts for underplanting are small spring bulbs (eg crocus, snowdrops) and perhaps some alpine plants - if you can give them decent drainage.
You could also consider herbs, which would be a nice transition between veg and flower garden. I grow chives as edging plants. They get to about 8" high and I love the purple pom poms. Dead head them en-masse and they often flower again.
I also grow curly leaved parsley, golden oregano and different thymes as edging plants - don't know how well they'd do where you are?
Just to say I wouldn't be in too much of a hurry to put in anything which offers too much competition with your lovely new trees.
Thank you for the suggestion - I do want the trees to thrive so I may well wait to plant up until spring 2022 to give the trees plenty of chance to establish well.