Sold by the Bulb. 
Today's Gladiolus (or simply glads as they are quite often called) are larger and more beautiful than varieties years ago and produce lush sword like foliage. They appreciate the warm weather of summer and are very easy to plant and grow. Gladiolus come in a wide selection of classic colors, as well as the newest bi-colors or tri-colors. You can plant them all at once after the danger of frost has passed, or plant them bi-weekly for continuous flowers throughout summer. They are best planted in groups and make for excellent lavish florist quality cut flowers. Black adds sophistication, formality, elegance and mystery to any garden. While not truly black, Black Beauty comes close.