TYPES OF LAVENDER:
(1) "True Lavender" (a.k.a. "Lavandula Angustifolia" or English Lavender): has short/medium flower stalks with concentrated flower heads on a single stalk; buds and blossoms come directly from the stalk; seeds are fertile; very suitable for oil production and culinary use.
(2) "Stoechas Lavender" (also known as "Lavandula Stoechas," "French Lavender," or "Spanish Lavender"): flower stalks vary in length; an egg- or pineapple-shaped flower head forms first with pseudo blossom on top and true blossoms up and down the side of the flower head in parallel, vertical rows; seeds are fertile; generally not suitable for oil nor culinary use (due to presence of unpleasant substances called "terpenes").
(3) "Spike Lavender" (a.k.a. "Lavandula Latifolia"): has very tall flower stalks and elongated, but concentrated blossom clusters. The stalk usually has flowering branches instead of solitary flower stalks. Seeds are fertile. Good for oil production, but chemical composition (and hence aroma) is slightly different than True Lavenders.
(4) Hybrids (a.k.a. "Lavandins" or "Intermedia lavender"): are a cross between True Lavender and Spike Lavender (easily identified: botanical name includes an "x"). The seeds are sterile, so propagation is accomplished by rooting plant cuttings. Lavandins generally produce more essential oil than angustifolias, and all are suitable for culinary use. Long flower stalks make lavandins ideal for commercial (machine-harvested) production.
RECOMMENDED VARIETIES & CULTIVARS TO GROW IN NORTHERN CLIMATES:
(1) Perennials: any English Lavender rated for Zones 4 or 5. Munstead and Krajova (also known as “Czech” lavender) fare best. Provence, Melissa, and Phenomenal also generally fare well.
(2) Annuals: any stoechas lavender (also known as "French Lavender" or "Spanish Lavender") is a sure bet for annual gardens. Stoechas lavender tend to bloom for extended periods of time, although their aroma is not as sweet as True or Spike Lavenders or Lavandins.
HELPFUL PLANTING HINTS:
(1) A sunny location and well-drained soil are absolutely critical. Planting near a wall, building, or rock can also be helpful.
(2) Soil preparation is crucial: mix equal parts of rich topsoil and mulch or other organic matter (dried leaves or compost). Build a "volcano" with crater. Plant the lavender in the crater, then mound the dirt around the root and press firmly to remove air pockets. Water well every day for about a week until roots are established.
(3) Recommended soil pH: between 6.7 and 7.3
(4) Do not plant lavender past the 15th of September. Plants need time to establish roots prior to winter.
(1) Prune lavender only in the spring, while the plant is still dormant or once green growth is noticed, but prior to bud formation (usually the month of May). Do NOT prune lavender in the fall in northern climates, as this may kill the plant.
(2) Prune either the entire branch all the way back to the core (if a branch is dead or mostly dead) OR prune up to 1/3 the branch's length. Do not prune more than 1/3 per year.
(3) Light, cosmetic pruning throughout the summer and early Fall is OK, but save heavy pruning until Spring. It's OK to snip dead flower stalks any time.
(1) Do not allow a lavender plant to bloom during its first year (whether grown from a cutting or from seed). Pinching off buds/blossoms encourages root growth and will result in a bushy, compact plant.
(2) Cover your lavender with burlap in the winter to protect against winter's wind.
(3) Never split a lavender bush, as doing so will kill the plant. If your plant has overgrown its location, simply dig it up and move it to another location.
(4) Harvest bud stalks first thing in the morning (when they are the most aromatic). Bundle up to 100 stems together; tie with a rubber band; and then hang the bouquets upside down in a dry, dark area to preserve colour and aroma.