Xeriscaping can be done with preparation
Xeriscaping is derived from the Greek word xeros, meaning dry, and it doesn't mean that you need to develop a garden full of sand and cacti, but that you need to be highly aware of what you are planting and grow plants that have low moisture needs. Such plants can usually be determined from their leaves and their environment.
The first step is to look over your garden and determine where the garden is driest, where there is the most water and how you plan on landscaping the site. For example, most septic fields stay fairly moist year round, so growing cacti might not work too well on such a site. But at the top of a slope where moisture continually drains toward the bottom of the slope leaving the top dry might be a good place to put plants that can survive on little moisture. In Jamestown you probably do not want to go whole hog developing a totally xeriscaped garden. We get enough rainfall in spring that a more natural garden with some xeriscaped features will probably do quite well.
If you decide to make a xeriscaped area, you will need to improve the soil so that your plants can grow properly. That usually means a lot of compost to raise the amount of organic matter in the garden, a heavy mulch to prevent runoff of what little rain there might be and to keep the soil moist during dry spells, and careful watering so that you do not get growth spurts that require lots of water to continue. Some people like to use small stones or pebbles in their xeriscaped area. That's ok, but you should enrich the soil before laying your stones and remember that you may not be able to enrich the soil again without getting pebbles into the soil. If you are going to use small stones or pebbles as mulch, you might want to put a weed barrier down so that you can remove the stones by pulling the weed barrier aside without removing too much soil.
You will also need to select appropriate plants for your Xeriscaped area. Plants with glossy leaves usually retain moisture more easily than do large, softleafed plants. Plants for xeriscaping are usually derived from areas that are arid and dry, such as South Africa. Around here you will probably need to lift them at the end of the season and store them in the greenhouse or other frost free area. When selecting plants, look to see where the plant came from. Obviously a plant from a rain forest is not a suitable candidate for a xeriscaped garden, but a plant from a low moisture area might be a terrific candidate, provided it can take our winters. Some Xeriscape plants are listed here to give you an idea of what to plant in your garden.
Some Plants for a
Gaillardias - Colorful annual daisy-like flower from South Africa
Agapanthus - African Lily - needs to be lifted in the fall
Dianthus - needs alkaline soil, of which we do not have a lot of on the island. Add lime to change soil Ph for dianthus.
Gaura - a dainty plant that is marginal around here. Either bring indoors for the winter or mulch heavily.
Sunflowers - there are a large variety of sunflowers of many different sizes.
Thyme - an herb that grows well and has the added benefit that you can pick it.
Veronica - a showy plant that grows in fairly large clumps after a year or two. Will spread on its own from seed.