As with all gardening projects, it's best to start with a design in mind. Use a computer to download a digital picture of the space, then use design software to click and drag images until you have the layout you wish for your garden. We will create a 6' wood square, and drop in a second square at a 45-degree angle. Then each space within the squares will be planted with a different herb, and a narrow walkway will be created around the perimeter. Finally, a hedge of lavender and rosemary will be planted around the walkway.
We establish the sense of symmetry by first creating the main axis of the garden. We spray-paint a line that runs perpendicular to the preexisting espaliered fruit tree that we're using as a reference point. Then we create axes in the opposite direction by marking lines that run perpendicular to the first line.
Pressure-treated 4x4s with mitered ends are secured together with galvanized screws (Image 1) to form the exterior square frame (Image 2).
We use 2x4s to build the interior square, securing the ends as before and fitting the square inside the first one at a 45-degree angle so that the corners align with the painted axis lines (Image 3).
Now it's time to start filling in all the spaces with a variety of herbs. The herbs chosen for this garden will look and smell great, and they're also very long-lived perennials. First we spot all the plants, or set them in place while still in their pots. After everything has been spotted, we can begin digging.
The vertical center of the knot is a noble bay tree (Laurus nobilis) (Image 1). This herb was grown by the ancient Greeks and Romans and is the bay that is used in cooking.
Rosemary (Rosemarinus officinalis) (Image 2) is a perennial shrubby herb that will live for decades — once it's in the ground, you'll never have to replant it. This upright form of rosemary will form the hedge outside the knot garden and will provide intermediate height.
Two lavender varieties, lavender cotton (Santolina chamaecyparissus) and green lavender cotton (Santolina virens) (Image 3) are of similar stature but vastly different colors. Since the key to knot gardens is to use highly contrasting plants against one another to emphasize the geometry you've created, these two work beautifully together in such a setting.
East Friesland meadow sage (Salvia nemerosa 'East Friesland') (Image 4) was a popular perennial, but is too tall for this application. A new variety is perfect for knot gardens, however: it stays very low, produces perfectly sized little flower spikes and is very fragrant. This herbaceous perennial prefers good drainage and drier soils.
For the front section of the knot, high contrast is essential. Here it's provided by prostrate rosemary (Rosemarius officinalis 'prostratus') (Image 1). The green of this dense plant will provide a beautiful foil to the dusty color of the lavender behind it.
In the corner that fronts the green lavender plantings, Maureen plants a gray-toned Otto Quast Spanish lavender (Lavendula stoechas 'Otto Quast') (Image 2). Dwarf myrtle (Myrtus communis 'compacta') (Image 3), which goes in behind the purple sage, is very fragrant when cut. Frequent cutting is important to keep the plants in good form — and to provide plenty of material to bring into the house for culinary and other uses.
The final choice for the outer sections is variegated licorice plant (Helichrysum petiolare 'Licorice Splash') (Image 4), a very drought-tolerant species.
The soil should be dug out enough that the top of the lumber is visible about 1" above the soil level of each plant (Image 1). The bay tree goes in the center, planted deeper than the other plants because it has a larger and deeper rootball. Many of the plants will be placed rootball to rootball; any gaps will be filled in with good-quality topsoil (Image 2). Since the garden soil doesn't necessarily have to be placed back in the area, this technique works well in yards with less-than-ideal soil — even potting soil can be mixed in with the topsoil to provide better drainage.
All of the sections of the knot garden have now been filled in (Image 1), and we bring in more lavender — a different kind, and for a different purpose