Hey Mate

love your work. I can see you have a problem common to many swale makers, not enough planting stocks to "capture the site" in terms of maintenanance
see how your comfrey really thrives, that a great example of the weed suppressions its capable of
youll be mowing a lot over coming years till those trees get up
i f i may give some pointers based on my own experience, to reduce your workload and fuel bill , you can dig into that comfrety now, and pull up a bucket full of roots
those can be planted in a ring around and almost up the the base of your trees, it'll form a sward that will really help your trees by suppressing weeds
the comfrey spike roots will dig deep and are compatible with the fruit tree roots that are both surface and deeper
ive done this and it works great
in addition its good to look around your area, esp on old fields and forest edges and find short lived herbaceous legumes and other colonisers that can fill the gaps for a few years and be shaded out longer term
Lupins are great in cooler climates, Alfalfa/ lucerne is also good
shrubs like Elaeagnus are great gapfillers
its good to examine in wastelands what is growing and observe the successional colonisation, youll probably find all you need growing locally

also non seeding/ low seed clumping grasses like Miscanthus are great for mulch and wed suppression. They will shade out as the trees grow

jeruslaem artichoke is another good gapfiller