Answer: There are so many plants that would grow in that situation that it really depends on what look you are trying to achieve. Since the clematis and lavender have limited bloom periods, you might want to use annual flowers for extended color. You might also want to use smaller evergreens to provide all season interest, although the lavenders will provide some structure in cold weather. Or you could use a mixture of sun-loving perennials to extend the blooming season. In making your selection you will want to select plants that prefer full sun. Those close to the lavender should need the same extremely well drained conditions and average soil moisture levels as the lavender, those near the clematis should need a more evenly moist yet well drained soil. This way you can prepare your soil and do any supplemental watering accordingly. I would also suggest that you leave ample room for the clematis roots, they are somewhat fragile and wide reaching and need a cool, shaded area in which to run without competition from neighboring plants. For this reason you would not want to plant right next to it and you will want to leave the area under and immediately around the obelisk for them. Depending on the variety of lavender you grow, you will need to leave approximately two feet of spread for each of those plants. I am not sure how you measured your circle but if it is a diameter of five feet then it may already be full. Certainly you could plant some spring bulbs in between the center and the perimeter and/or a groundcovering plant such as creeping thyme or a low growing perennial geranium to make things look fuller while you are waiting for the lavender and clematis to mature. Good luck with your planting!
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