I think this works well as it is Jane, with great texture and contrast. When you ask should I do more -I would say yes but new compositions. If it is relatively small (you said postcard size) then a series of three or four different views of your garden, using the same approach would be really interesting and enable you to explore and push the technique further. When I was in Vienna there was a massive exhibition in the Leopold Museum of national Richard Gerstl -I wonder if you have come across him? He used paint in a similarly textural and abstract way in his garden and landscape paintings. You might find it instructive to look at his work
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