If you mean Spanish Lavender (L. stoechas), it has a tendency to bloom once in the spring, and just grow through the summer. French Lavender (L. dentata) blooms more often, but the actual flowers aren't very showy, and the bracts are only colored at the tip of the spike, and not as showy as Spanish Lavender.

I find cutting the lavender stalks down once flowered helps the new flowers come through more vibrant... I might be wrong though x

That helps if it is a re-blooming species--almost all except L stoechas. Other things that help the color to pop: full sun, fast drainage, cool nights, and/or a bit of magnesium (epsom salts or dolomite).

oooh I'll get some epsom for it, thanks tugbethil