Blue flax (Linum perenne) withstands periods of heat and drought, growing in landscape areas where other flowering perennials will not. Hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9, it requires full sunlight and well-draining soils to thrive. Part of maintaining blue flax involves cutting its stems back twice per year to keep it tidy.
Used in mixed flower beds, borders, rock gardens and mass plantings, blue flax grows in an upright, mounded form that adds texture, filler and color to its surroundings. This herbaceous perennial reaches 1 to 2 feet in height with a spread of up to 1 1/2 feet. Its sword-shaped, 1-inch long leaves sport a bluish-green color, adding contrast to the landscape when it's not in bloom. Blue flax blooms over a period of eight weeks, beginning in late spring to midsummer. Each star-shaped blue flower lasts a single day. The cultivar "Alba" (Linum perenne "Alba") produces white flowers.
As its blooming wanes in midsummer, the blue flax plant turns its energy to converting the flower heads into seed capsules. Removal of the spent flower heads will divert its energy back into producing green growth and a possible second flush of blooms. To remove all the flower heads, but avoid stunting the plant's growth, cut off the top one-third to one-half of each stem. This heading-back process also helps the blue flax remains compact and thick, preventing its growth from becoming spindly, leggy and flopping over. Water the plant thoroughly after cutting it back to reduce shock and encourage new growth.
After the blue flax finishes its second round of flowering, it will once again concentrate its efforts into producing seed. If you want the plant to produce, and drop its seed naturally to create a flush of new plants in the spring that will widen your stand of blue flax, wait to cut the plants back until they release their seed. To promote thick, compact spring growth, cut back the flax before winter ends, prior to the plant breaking out of dormancy. Prevent the plant from producing seed, becoming spindly or falling over, by cutting its stems back after flowering finishes in the fall. Whenever you choose to prune your blue flax plant, cut each stem off 1 inch above ground level.
Using the proper tool to prune your blue flax plant prevents unnecessary damage to the stems, ensuring that the cuts heal properly so new growth can occur. When pruning blue flax plants, use scissor-type, hand-held pruning shears. This type of pruning shear makes smooth, clean cuts, and will not crush the flax's thin stems. Always sterilize the pruning shears before and after pruning by soaking their blades in a 70 percent alcohol solution for at least five minutes. Sterile blades will prevent the spread of disease, keeping your blue flax healthy.