There are many types of Celtic knots. For a rose knot garden, the simple triquetra design is often the best place to start. Love knots and basic circle designs are simple yet elegant enough to make your rose knot garden breathtaking. There are countless variations on these designs so try to find one that suits your landscape the best.
Roses come in a variety of colors, from pink to orange. For the lines of the design, pick a color that will stand out in stark contrast to the color of the roses that will be filling in the spaces located on the inner and outer parts of the knot. For example, variations in shades of pink, such as blush and magenta, make a pleasant contrast. White and red are a classic combination. Or, if so inclined, choose bolder contrasts like yellow and lilac.
Roses best suited for a knot garden are those that are hardy and can withstand a good deal of trimming; which is going to be required to maintain the shape of your design. The American Rose Society has a list of some of the best and easiest to grow garden roses. Be sure to reference a U.S. Department of Agriculture (USDA) plant hardiness zone map to ensure that you purchase the correct type of rose for your area.
Antique roses and dog roses (Rosa canina) are good, hearty breeds that can withstand the grooming necessary to keep the outline of the knot in place. Dog roses may not be the first choice for many rose fanciers, but these breeds constantly provide blossoms throughout the growing season. They aren't difficult to care for, which makes them a good place to start for beginners. If you wish to be creative you can even use miniature tea roses for borders that require height differentiation.
Know the dimensions of the site for your rose knot garden before you sit down with graph paper. Take care to draw out the garden plot based on those measurements. Designate specific planting areas with colored pencils or something similar so that when you go to plant, you know which color of rose goes where. Be sure to leave enough space between the shapes you have created so that the knot is clear to the naked eye.
Prepare the area that you are going to plant by tilling the soil. If it is not level, some additional landscaping may be required to make it a flat surface. This may be done with a lawn roller or just a bit of digging and raking to level it out.
Measure out the design according to your plans, then mark off the different planting areas of the design with stakes and string. Plant the roses for each area of the design evenly, making sure to give them plenty of growing space. Be sure to trim your roses once a month during the growing season to maintain the knot's shape. With proper tending, your rose knot garden will delight for years to come.