Penstemon 'Firebird' AGM. This is one of the most popular penstemons for its spectacular and long lasting flowering season. It was breed for its persistence, the tubular flowers are a bright red with internal veining that almost glows. Forms a bushy plant to 3 ft. A brilliant garden plant. Penstemons can flower for up to six months of the year. They are best grown in a sunny or partially shady spot in the border, on a moister garden soil but will tolerate drought. Penstemon are resistant to slugs and other pests and attractive to bees. Hardy Perennial.