Q. Can you recommend a Dwarf Lavender for zone 7a?
Although lavender prefers a Mediterranean-type climate, it can be grown successfully in the Northeast if a few basic rules are followed. You will need to choose between the hardier Lavendula angustifolia hybrids and the humidity tolerant Lavendula x intermedia. No lavenders work perfectly in our area and the best choice for you will depend on the exposure of your site.
For our climate, the hardy English lavenders (Lavandula angustifolia) are the best bet at braving the winter cold. There are at least 100 cultivars of L. angustifolia, differing in flower color, scent, and growth characteristics. Most of these plants grow a grows a bit taller than you are looking for (24 to 36") but 'Hidcote', 'Little Lottie', 'Lavenite Petite' and 'Melissa Lilac' all grow under 2 feet and 'Nana Alba' and 'Thumbelina Leigh' grow just 10 to 12 inches tall. The smallest two plants are also less dense and will not give you the strong hedge-like border of the larger plants.
Lavandins, Lavandula x intermedia, are hybrids between L. angustifolia and L. latifolia. They are more tolerant of humidity and are hardy to Zone 7--suitable for the southern regions of the Northeast. 'Alba' (a white-flowered lavender), 'Grosso' and 'Provence' are good choices to try but all these cultivars grow taller than you are looking for.
All lavenders do best in very sunny locations (6-8 hours of sun per day) and need good drainage. If your soil is heavy, drainage can be improved by adding grit or coarse horticultural sand to the soil. They also prefer a neutral or slightly alkaline soil. If your soil is acidic, add lime to raise the pH (but not above 8.5). Lavenders can also be grown in pots. Use a free-flowing medium; water and fertilize regularly. As lavenders have an extensive root system, make sure to plant in a large container.
Prune your lavender regularly to reduce woody growth--woody plants produce fewer flowers. Prune in early spring when new growth has appeared. Lavender can also be trimmed in summer when flowering is finished. Bigger plants can have a third of their branches cut back every year or two.
Hope that helps you get your lavender off to a good start!
- Courtesy of NYBG Plant Information Service