By June, most gardeners have a pretty good idea of how their borders are shaping up. Spring bulbs may have finished flowering, leaving empty spaces behind, while some perennials might be growing more slowly than expected. And occasionally, a plant doesn’t survive the winter — I’ve had to say goodbye to more than one perennial that was hit too hard by cold weather.It’s something that can happen to anyone; even well-planned gardens sometimes end up with unexpected gaps once the growing season gets underway. But those bare patches can make a garden look unfinished, drawing the eye away from your best plants and disrupting the flow of a border.Filling those spaces allows you to add color or contrast, all while creating a fuller, more cohesive display that looks intentional and well-established throughout the summer months.Fortunately, even if you’re short on time, you don’t need to spend a fortune on mature plants from the garden center. Fast-growing annual flowers can go from seed to bloom in a matter of weeks, quickly filling empty spaces with foliage, texture, and color.They are also a budget-friendly option — a single packet of seeds often costs less than one nursery-grown plant.If you’re looking for the quickest way to make your garden look fuller this summer, here are seven flowers to sow right now.1. Sweet alyssum