’Tis the season for sharing gifts from the garden

Now that we have rain and cool temperatures, it’s time for the season of sharing. Luckily, it’s also the best time to edit our gardens, sharing the extras with friends and family.

Autumn is the best time to edit our gardens and divide plants or dig up seedlings. Plants are becoming dormant or semi-dormant and are much less prone to transplant stress now. As we cut back and clear our gardens and rake leaves, the true condition of our plants is revealed.

Some may have increased and spread laterally, others may have died and some may have developed bald spots in the middle. Seedlings may be emerging around some plants, with germination stimulated by cooler temperatures and increased moisture.

This is a good time to assess what is left in the garden and decide what you want more of or whether you want to curb the spread of ambitious growers and give pieces of them away. Also, some perennials begin to decline after a few years and need dividing to maintain strength. You can move extra plants or divisions to other locations or give them away.

Perennials aren’t perennial forever

A common misconception is that once planted, perennials will be just that — perennial, living for years hardly tended. But the life spans of perennials vary greatly. Some live for many years and don’t need division, like peonies or baptisia. Others, like many hummingbird mints, may last just a couple years. Plants like the aster ‘Monte Cassino’ need dividing every two or three years to keep them youthful and vigorous. Plants with a tendency to spread, like monarda or Shasta daisies, may need some curbing every year or two to prevent them from taking over a bed. Perennials like gaura and the tall purple verbena, Verbena bonariensis, can seed profusely. Seedlings should be thinned.

When trying to decide how to approach each plant, simply observe the perennials after they have been cut back to determine how they grew.

An easy place to start is to identify the spreaders. These are plants that spread horizontally across the soil, with clumps growing noticeably larger and larger in size each year. Some, like mint, do it somewhat surreptitiously by sneaky, difficult-to-find underground rhizomes. Others, like monarda, some asters, some yarrow (Achillea millefolium types), Japanese anemone, Shasta daisies, some chrysanthemums, goldenrod, California fuchsia, Salvia uliginosa and ornamental oregano, spread mostly along the ground surface.

Growth is dense and easy to spot. You can curtail it fairly easily by regularly slicing off unwanted portions with a shovel. Plants with mint-like tendencies include stoloniferous Aster chilensis and Oenothera berlandieri. It’s difficult to find and remove all the delicate small roots from areas where they have become undesirable. All spreading plants need thoughtful siting in the garden and regular maintenance, but in the right place they can be very beneficial.

How do you know when to divide?

Bald spots developing in the middle of a plant are an indicator that you need to divide it. These bald spots show that the older part of the plant — the middle — is declining with age. Look closely, and you’ll likely see fresh, strong new growth on the perimeters of the plant.

Many perennial plants lose vigor and die over time, even as growth continues on the edges of the plant. To reinvigorate the plant, cut it into several pieces with a shovel and replant the vigorous pieces or give extra ones away. Mix in or mulch with compost to renew soil nutrients.

Many perennials, like sneezeweed (Helenium), spread slowly into largish clumps. You can leave these as long as you like. If you want to spread the plant around your garden or give away some clumps, you often can slice the clump into two to four pieces with a shovel, taking care to include as many roots as possible. Replant them as soon as you can. Some examples of plants like this are sneezeweed, agapanthus, Aster cordifolius, heuchera, native wild iris and daylilies. If you see weak portions, that means it’s time to divide the plants.

Plants that seed excessively (in some sites), like Gaura or tall verbena, also decline in strength after a year or two. It’s best to replace them. You may want to dig out the parent plant in the fall and replant with a vigorous seedling. Either discard the unwanted seedlings, give some away or pot some up. Plant them about 3 feet apart.

Over time, you will begin to recognize plant growth types and know about how often they need division.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at: katebfrey@gmail.com, Twitter @katebfrey, Instagram @americangardenschool