With their silvery foliage and wands of sweet-scented flowers, often added to sachets, lavenders (Lavandula spp.) make striking additions to both flower and herb gardens. Hardy in U.S. Department of Agriculture plant hardiness zones ranging from 5 through 10, they vary in size from the diminutive 6-inch-tall “Thumbelina Leigh,” an English lavender (Lavandula augustifolia, USDA zones 5 through 10) cultivar, to the up to 4-foot-tall French lavender (Lavandula dentata, USDA zones 8 through 10).
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Choose and Improve Your Site
A lavender plant prefers fast-draining sandy loam, with a pH between 6.5 and 7.5, in a position where it will receive full sun or at least six to eight hours of sunlight per day. Under those conditions, you can get away with setting the plant directly in the ground.
If the soil in your garden is heavy clay instead, spade some pea gravel or sand and compost into the top 1 foot of it to build a flat-topped mound into which you can set the plant. That mound should be about 1 foot high and 1 foot wide and made up of 1 part soil, 1 part pea gravel or sand, and 1 part compost. In areas where your selected lavender is only marginally hardy, such as USDA zone 5 for English lavender, position the mound near a stone wall, sidewalk or building.
Space and Plant Your Lavenders
If you have more than one plant, space them 1 foot to 3 feet apart depending on their mature size. Should you prefer to make a hedge out of such traditional hedge types as Provence lavender (Lavandula x intermedia "Provence," USDA zones 7 through 10), set them 12 to 16 inches apart for plants whose ultimate height is under 2 feet tall, and 16 to 18 inches apart for plants which will surpass that height.
About four to six weeks before your last frost date, dig a hole slightly larger than the plant's pot, either in the garden bed or in the center of the mound. Add 1/6 cup bone meal, 1/6 cup composted manure and 1/6 cup of lime to the bottom of that hole, omitting the lime if your ground is already alkaline, and work the amendments into the soil.
Cover the amendments with a little additional soil before setting the plant in place, loosening the roots first if they have become congested, at the same level it grew in its pot. Once you have filled in soil around the plant’s roots, water it well and mulch it with 2 inches of pea gravel, sand or poultry grit, keeping mulch from touching the base of the plant.
Water and Fertilize Your Lavenders
For the lavender's first growing season, water it whenever the surface of its soil dries out. In its second year, it shouldn’t require irrigation except during drought conditions.
In autumn each year, strew another 1/6 cup bone meal, 1/6 cup composted manure and 1/6 cup of lime around the base of the plant and water it into the soil. Refrain from using high nitrogen fertilizers, which may inhibit flowering.
Plant and Tend Container Lavenders
To grow a lavender plant in a container, choose a pot at least 12 to 16 inches in diameter, with drainage holes in the bottom. Cover the drainage holes with 1 to 2 inches of gravel or packing peanuts, and add a mix made up of 2 parts potting soil and 1 part horticultural grit. Before setting your plant in place, work 1 tablespoon of garden lime thoroughly into that potting mix.
Dig a hole in the center of the pot and position the plant so that the top of its root crown is 1 inch above the surface of the soil. After patting the mix firmly around those roots, strew 1/2 cup of alfalfa pellets over the surface of the mix, water it thoroughly and mulch it with 2 inches of pea gravel or poultry grit. Water the pot whenever the surface of the mix beneath the mulch feels dry.