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Moving season for perennials and shrubs

Hardy plants, trees do well when transplanted in the fall

Goldmound spirea The fall is a perfect time for planting. Above, a Goldmound spirea shrub gets a new home. (Pat Greenhouse/Globe Staff)
By Carol Stocker
Globe Correspondent / September 30, 2010

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Late September and early October are great for planting perennials, shrubs, and trees. The soil stays warm long after the air turns cold, encouraging root growth, and rains are frequent enough that extra watering is seldom needed. It’s also the most pleasant season to do vigorous work outdoors.

In terms of cost, you’re also in luck. Nurseries want to unload excess inventory, so shop the sales and be flexible about your choices. And don’t buy evergreens. They do better with spring planting.

The fact is, most hardy plants actually prefer fall planting. If your site has less than eight hours of sunlight a day, be sure to buy plants marked “part shade.’’ Read the labels and check for ultimate height and spread; you don’t want a tree or shrub growing right up against your house or garage.

Smaller size plants tend to be much less expensive and easier to plant than larger specimens, and often reach full size just as quickly. You should be able to plant perennials and small shrubs by yourself, but planting larger shrubs or young trees is often a two-person job.

Whether you’ve bought trees, shrubs, or perennials, the general rule for planting is to dig a hole that is the same depth as the root ball, but wider. Use a sharp-edged spade or shovel with a strong handle for digging deep holes, cutting through sod and levering out rocks. If you’re working in a border that has been mulched, scrape the mulch off the area where you are going to dig and layer it back on top afterward.

Dig the hole, shoveling the dirt into a wheelbarrow where you can mix and enrich it with compost (which you can buy in bags) and a sprinkling of lime and super phosphate. Then, dig an inch of this amended soil back into the bottom of the planting hole. Knock your plant from its pot and use a three-pronged hand cultivator to lightly loosen the outside of the root ball and the sides of the planting hole. Place your plant in the hole so it is at the same depth at which the soil ball sat in the container. It’s OK if it’s an inch higher, since soil will settle, but the top of the root ball should never sit lower than the surrounding ground. (If you’re planting shrubs or trees whose root balls are wrapped in burlap or some other material for transporting, unwrap and untie the root balls before planting and remove the material.)

Mix the soil you dug from the hole with compost and after putting the root ball in the planting hole, fill in around the sides halfway. Then fill it to the brim with water. After the water is soaked up, fill the rest of the hole with soil along the sides, but don’t cover the top of the root ball. You can use leftover soil to build a low berm around the plant just outside the original hole to hold water close to the plant. Then water again. After that, you can mulch inside this well if you want, as long as the mulch doesn’t actually come in contact with the trunk or stem of your new plant. The mulch should look like a plant growing out of the doughnut hole, not like a volcano piled up around the new plant’s trunk.

If you order plants such as roses through the mail, they may arrive bare-root, which means without soil, because that makes shipping cheaper. Unpack them immediately and let them soak in a pail of water for a day before planting. Bare-root plants die if their roots dry out, so don’t let that happen. If you can’t plant bare-root trees and shrubs right away, lay them on their sides and cover the roots with soil temporarily to keep them moist. When planting in their permanent spots, set them at the same depth at which they grew in the nursery. If you cannot determine this, plant the topmost roots three inches below your soil line.

Suppose you want to move established plants to a new location. It’s easy to move perennials but transplanting trees and shrubs is physically more difficult than purchasing and planting a new one, because there will be extended roots to deal with. So think twice. It’s often not worth the risk to the plant or your back.

If you proceed with transplanting, wait until after the woody plants lose their leaves so they are dormant. You will probably need to dig down no more than a foot to excavate a perennial. Dig down at least two feet all the way around a small tree or shrub you want to move. After that, work your shovel, spade, or garden fork inward under the root ball. If the plant does not lift immediately, you may have to work your way around it several times, each time getting farther underneath and rocking the root ball toward the opposite side of the hole until the plant loosens and lifts free. If you are trying to move a larger specimen, you can slip a plastic or burlap sheet underneath, while rocking the plant to one side, and then the other. Once you have excavated a shrub or perennial, if it has many separate stems, you can divide it into pieces by gently pulling the roots apart with two spading forks and replanting them in suitable size holes, much as you would for bare-root plants. Each piece should grow into a full-size plant.

To protect new plantings from drying winter winds, cover them with several inches of mulch, such as chipped bark. You can also use fallen leaves that have been ground up by a leaf vac or mulching mower as free mulch that will add organic matter to the soil as it breaks down. Whole fallen pine needles work well, too.

Carol Stocker can be reached at stockergarden@gmail.com.