Well in my opinion the month of June is when our gardens look their best. You could fill said border with a variety of scented and flowering shrubs, roses, honeysuckle, clematis, with lavender at the front, whatever you like, your choice. The garden centres will have loads for you to choose from and will give you good advice. If they are not to be permanently in situ until you get your hard landscaping done I would just leave them in their pots but submerge the pots beneath the soil then nobody will know they are not permanent. When your landscapers arrive you can just life them up and plant them in their permanent positions.