Do You Cut Back Blue Flax in the Fall?

About Blue Flax

• Blue flax grows 18 to 24 inches tall and 12 inches wide in full sun in soil with good drainage. Best used en masse in rock gardens or at the fronts of borders, each flower blooms in the early morning and typically drops by late afternoon. There is a profusion of flowers, however, and they can be in bloom for up to 12 weeks in summer. Because their roots can be shallow, blue flax plants don't overwinter well in cool climates when planted in clay, where they may only last two to four years and where roots can rot. The plants are more long-lived in sandy soil where they can put down long taproots and water doesn't pool.

New Plantings

• Cut back newly planted blue flax back by one-half with shears to promote bushy new growth, as they tend to become spindly and floppy. Plants that are not trimmed may flower in late spring in their first year, even when started from seed; the plants are used as annuals where soil and drainage are poor. Trimmed plants have more compact growth and bloom beginning in midsummer.

Established Plants

• Established blue flax plants can start to open up at the center and flop over in midsummer. Prune them back by one-third to one-half after flowering. They will bloom again, but the flowers may be smaller. Water them right after you prune them to encourage regrowth. You can give them another light shearing after they flower again to keep them compact, if necessary. Cut the plants down to their basal growth in late winter to early spring before new growth begins.

Self-Seeding

• Deadheading, or removing old flower heads, helps control the plants' tendency to self-seed. When you cut blue flax back after flowering, you shear off the potential seed heads. If you shear them back after their last flowering, you may want to leave several plants as is if your plants have been in place for several years. Seeds drop as the seed heads mature to start new plants in the spring to replace those that may die out. On many flowers you can often just pick off the old flower heads, but flax stems, though they look delicate, are fibrous and difficult to break, so shearing is the best choice for deadheading.