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All About Lavender - 1/16/2015
by Jim & Dotti Becker
All About Lavender
English lavender 'Bettys Blue' English lavender 'Premier' lavandin 'Alba'
No matter where you garden, lavenders need full sun and a well drained soil. There are about 30 species and hundreds of cultivars, all belonging to the genus Lavandula. Most are native to lands around the Mediterranean Sea and it is not surprising that they do best in similar climates, like California. Fortunately, the large diversity of lavenders offers a range of suitable growing conditions, and while you can’t grow all types of lavenders in all parts of the U.S., with proper planning there can be a lavender for almost everyone.
The first trait that separates which lavenders will successfully grow in your area is cold tolerance. The hardiest lavenders, cultivars of Lavandula angustifolia (often called English lavenders) and L. x intermedia (lavandins), survive down to USDA Zone 5a. Some gardeners tell us they find the English a tad bit hardier than the lavandins. If you live in a colder zone, you will need to grow lavenders in pots and bring them indoors for the winter. These very cold hardy lavenders will also grow in warmer zones, though some gardeners find that they do not flower well in frost-free climates.
English lavenders, lavandins, and their many hybrids, do great in hot dry summers, but poorly in areas that combine heat, summer rain, and high humidity. These climates promote the biggest lavender killers: fungal diseases. The best plants for these regions are French (Lavandula dentata), Spanish (L. stoechas), and fernleaf (L. multifida). French lavender is a tender plant with a blocky flower spike topped by a small tuft of pale purple bracts. Its leaves are slightly indented all along their margins, as if cut out with pinking shears. Both flowers and foliage are thickly resinous with the scent of lavender and camphor. Unfortunately, it is only hardy down to USDA Zone 9a. There are, however, two French hybrids that offer more of the traditional lavender look and fragrance, do well in humidity, and are a bit cold hardier: sweet lavender (L. x heterophylla, Zone 8b) and L. ‘Goodwin Creek Grey’ (Zone 8a).
Fernleaf lavender can only be grown as a perennial in the warmest parts of the country. Visitors to our garden usually don’t recognize it as a lavender. It has deeply divided fern like foliage and an earthy aroma that reminds us more of herbs like hyssop or catnip. We often grow it as an annual since it blooms continuously its first year
The other choice for humid areas is Spanish lavender (L. stoechas). Its flowers are similar to those of French, though with much larger and more colorful top bracts and more cold tolerance (Zone 8a). The growth is distinctively low and sprawling; the scent is lavender mixed with pine.
The trickiest places to grow lavenders are hot, wet, and humid in the summer, but with winters too cold to grow ‘Goodwin Creek Grey’ or Spanish lavenders. Success here depends on maintaining good air and soil drainage. Gardens with the cooler, breezier summers often found at higher elevations will probably do the best. Lessen the chance of fungal problems by amending the soil with inorganic particulates like chicken grit and by mulching with grit or sand. Avoid organic mulches. Increase air circulation around the plants by planting on mounds or raised beds, which also helps soil drainage, and by not crowding the plants together. Space English and Spanish lavenders at least 2½’ apart; lavandins 3’.
We plant a variety of lavenders to assure flowers throughout the growing season. The Spanish bloom first, followed by the English and then the lavandins. A few cultivars will bloom on and off throughout the summer. We especially favor the darkest purples among the English and Spanish. The much taller lavandins have longer stems and larger, lighter, flower spikes that add grass like elements to the landscape. White flowered forms are quite stunning and show off well against a background of dark foliage.
Its important to note that the lavender flower is made up of two parts, the corolla and the calyx, each with a different color. The tubular corollas, what we usually think of as the petals, are most often violet colored, though some are white or light pink. The calyx colors range from a very deep purple to a light violet/green. When lavender flowers dry, the corollas fall out or shrivel up and only the calyx color remains. So when you choose a cultivar for dried flowers its only the calyx color that matters.
Most lavenders bloom only 4-6 weeks each year, so choosing cultivars for growth habit and foliage is just as important as for flowers. There are a number of hybrids, like ‘Silver Frost’, that have exceptionally silvery foliage and are real standouts. The creamy white and green leaf variegations of L. angustifolia ‘Goldburg’ and L. x intermedia ‘Walberton’s Silver Edge’ offer another color choice. The dentate leaves of French and its hybrids add a finer texture to these shrubs.
Most lavenders can be clipped into edgings, neat mounds or low hedges. Some cultivars are easier to keep trimmed than others, and of course there are large differences in heights and widths. Spanish lavenders are tough to tame and must be appreciated for their sprawling, more natural appearance. We shape all of our lavender plants lightly in early spring just before new growth begins and again in midsummer after we harvest or deadhead the flowers. We avoid severe pruning unless absolutely necessary, as it sometimes is with broken limbs or dead branches. Lavenders don’t reliably sprout new growth from cuts made on old woody stems
Lavenders do not demand a lot of water, but it is important to keep the soil evenly moist the first season or two. Once the plants establish a good root system, watering is drastically cut back. Drip irrigation is ideal for lavenders. Overhead watering is fine for the dry western states, but increases fungal problems in humid areas. If you must water overhead, do it early in the day so the foliage and flowers can dry out before nightfall.
Lavenders are not heavy feeders, but do require fertilizer, especially the first three years of growth. A fertilizer that is roughly equal in its proportions of N-P-K is best. We use a blend of 2 parts commercially composted chicken manure and 1 part kelp meal. About ½ pound of this mix is dug into each planting hole, and another ½ pound is scraped into the soil around each plant in subsequent springs. Chicken manure has an antifungal component, an added bonus.
choosing Lavenders For Your Climate
This is the best area to grow lavenders. Your choices of plants are limited by your hardiness zone. Some Western areas receive large amounts of winter rainfall; these must provide excellent soil drainage for success. The summer monsoon area of Arizona is a Western oddity and does best with the recommendations for the Mid-Atlantic States
High humidity combined with summer rain and heat is a big problem. Grow Spanish, L. multifida, French and the French hybrids, depending on your zone. The cooler winter areas of Zones 7 and 8 can try English and lavandins, but soil and air drainage must be excellent. Even then, the success and life spans of the plants will be diminished.
Mid-Atlantic and Southeastern States
These areas are too cold to grow some of the humidity tolerant lavenders, but try L. ‘Goodwin Creek Grey’, L. x heterophylla, and Spanish. Success with English and lavandins depends on good air and soil drainage. Gardens with the cooler, breezier summers often found at higher elevations will probably do the best.
Midwestern and Northeastern States
The cooler and breezier the summer the better you will do with lavenders. It is important to have good air and soil drainage. Upper states may be too cold to reliably grow any lavenders. Some gardeners tell us they find the English a tad bit hardier than the lavandins. Gardeners here should plant in sheltered areas or try winter protection like insulating fabrics or evergreen boughs. Don’t insulate too tightly; the plants need some air circulation.
English lavender 'Graves' Spanish lavender 'Willowvale' Lavandin 'Grosso French lavender
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