UNITED STATES—Mathematically, division is the opposite of multiplication. Horticulturally, they are the same. Digging and splitting overgrown perennials to propagate them is known as ‘division’ because it divides many rooted stems or rhizomes of one plant into many new plants. Division is a form of propagation; and propagation is commonly known as multiplication. So, we divide plants to multiply them.

Autumn is generally the best time for panting. It is after most of the warmest and driest weather, and just before the cool and rainy weather that keeps newly planted plants from getting too dry. It seems obvious that autumn would also be the best time for division. However, a few perennials that are dormant or mostly dormant by the middle of summer can be divided now for an early start.

Bearded iris may not look dormant with their leaves still green, but they are about as dormant now as they will get. If divided now and allowed to slowly disperse roots through the remainder of summer, they can prioritize the production of new foliage when they come out of dormancy in autumn, like they would do naturally. Like many perennials in mild climates, they grow through winter.

Once dug, the plump rhizomes need to be separated from the old shriveled rhizomes that they grew from. For most, the best segments of rhizome are between the leafy tips and the stalks of the flowers that bloomed earlier this year, although it may not be easy to see where floral stalks were attached. The older sections of rhizome behind the flower stems are probably shriveled already.

The freshly divided segments of rhizome should then be groomed of deteriorating old leaves. Remaining green leaves can be cut in half to remove drying tips. Rhizomes then get replanted just below the surface, with the perpendicular fans of foliage standing upright. The main difficulty with dividing iris now is that they will need to be watered until the rain starts late in autumn. Bergenia, lily-of-the-Nile and a variety of perennials with big rhizomes get divided in a similar manner.

Highlight: Kashmir cypress

Plants are usually well suited to the climates that they are native to. Glaucous (slightly reflective grayish) foliage is more common in harsh climates where darker green foliage might get cooked by the sun. Pendulous growth is more common among plants that want to shed heavy snow efficiently. Kashmir cypress, Cupressus cashmeriana, has both, but is from a tropical monsoonal climate.

It is a stately tree that can eventually get taller than 50 feet. Within its native range in the eastern Himalaya, old trees can get three times as tall! Limber stems might hang downward several feet. The minute scale leaves are neatly set on limber stems arranged in flat sprays, similar to, but more defined than those of arborvitae. Foliage is silvery grayish green, and perhaps slightly bluish.

Mature trees do not need much water, but would probably be happier if watered occasionally through summer. Kashmir cypress is unfortunately susceptible to the same diseases and insects that afflict Leyland cypress. That is a serious risk to consider before planting prominent specimens. Incidentally, Kashmir cypress is also known as Bhutan cypress, and is the national tree of Bhutan.