The brown buds that you are seeing are a result of wetness on the plant as well as at the roots. Without examining the blooms, I can't tell you if it is a fungal infection (which prosper in damp conditions) or something else, but water is at its source with near certainty.

For our climate, English lavenders (Lavandula angustifolia) are the best bet. 'Munstead' and 'Hidcote' are two popular choices. There are at least 100 cultivars of L. angustifolia, differing in flower color, scent, and growth characteristics. These varieties are worth exploring.

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 all good choices to try.

General growing advice is as follows: 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). Give each plant lots of air circulation to reduce the negative effect of local humidity.  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.

Courtesy of NYBG Plant Information Service