A lot of your favourite border plants, such as aquilegias, will have finished flowering and produced prominent seed heads by now. It is easy to collect the seed to sow for new plants of your own, just snip off the stem and seed head, and put it in a paper bag. Put the bag in a dark dry place, and after a couple of weeks the seeds will have dropped out and you can collect them, put them in labelled bags, and keep them for propagating in the autumn.