Box is the ideal plant for knot gardens because of its neat habit of growth but it is relatively slow-growing so an instant finished effect is not easy to achieve. It also has varieties with bright-green leaves, dark-green leaves, silver-edged, olive-green leaves, so you can create a knot garden using only box varieties. This will also be a more manageable scheme for a knot garden than using plants with different rates of growth and heights when mature, especially if you are at your first garden of this kind.
There are still some other herbs that can be used in a knot garden even they are not as neat and compact as box. The following herbs are good choices: Teucrium chamaedrys with glossy, dark-green leaves; Santolina chamaecyparissus with silvery foliage; Santolina rosmarinifolia and Santolina viridis with acid-green leaves; Hyssopus officinalis with dark green foliage; Lavandula angustifolia Hidcote with silvery foliage.
To make a simple knot garden you will need: the design, tape measure, string, short lengths of cane with pointed ends, builder’s set square in proportion 3:4:5, plastic bottle and fine sand, box plants.
For a successful knot garden make sure you prepare the site well before planting by digging in some garden compost or manure because it will be difficult to add organic matter once the plants are established. Also make sure that the area is completely level.
Accuracy of measuring out the design and putting in the plans is essential. A large set square made of lengths of wood nailed together in the proportion of 3:4:5 will ensure accurate 90 degrees angles at he corners. Draw the plan out on graph paper in measurements to suit your plot, preferably no bigger than 3-4 square meters. Color in the design to represent the plants you will use so you can achieve the effect of interwoven ribbons.
Use the plan then as a guide to mark out the squares on the ground using the tape measure, string and the short lengths of cane. Find the center point of each side of the outer square and mark the semicircles by drawing arcs with string attached to a cane. For accuracy make sure the stings are having the lengths of the radius of the semicircles. Mark out the semicircle with the pointed canes and attach the string tautly to define the curve. Mark out the rest of the design with string and canes making sure you measure everything carefully.
To define the pattern fill a plastic bottle with fine sand and pour it out evenly along the lines of the string and all markings, then remove the string and cane. Put in the plants spacing them evenly, 15 cm apart and keeping accurately to the markings. Follow the color code on the plan making sure the interwoven effect is achieved by putting he right color plant at the intersections.
As we say it above the box is a slow-growing plant so it will take 2 to 3 years for the plants to develop and close the gaps. In the second year pinch out the centers and trim lightly the plants to encourage a bushy growth. Once the plants have filled the gaps you can clip them twice a year, in late spring and early autumn, to keep them in shape. Avoid clipping if there is any danger of frosts as the new growths are soft and will be easy damaged by it.