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When you buy perennials online, usually they are shipped as “bare-root”, which means that the soil has been washed away from the roots after the plants were dug from the field, or removed from the container. Depending on the plants, sometimes the roots are also trimmed. The purpose of this is primarily to lighten the container prior to mailing, and so that the roots can be wrapped in moist newspaper. Postage is expensive and the last thing you want to do is to pay for the mailing of soil.
When you receive these plants, planting is done by creating a small mount of soil at the bottom of the planting hole. The perennial is then placed on top of the mount, and the roots are gently fanned out above the top. The roots are covered with more soil and watered in well. These types of planting tend to create anxiety with new gardeners, but really, there is no reason to. Bare root perennials are typically very sturdy and can easily be transplanted in this manner.
Because the gardener spreads out the roots in the process of planting, bare-root perennials tend to establish themselves quickly in their new environment.
The only thing to watch out for is how deep the crown should be planted. The crown is the central hard mass between the green leaves and the roots. Some plants should have the crown planted at soil level; others should have the crown just below soil level. Typical mistakes involve planting the crown too deeply.
While bare-root perennials may at first glance appear more difficult to handle than container-grown plants, in the end, they tend to establish themselves faster and better.
At garden centers most perennials are purchased as pot-grown, or container-grown. This means that the plant is displayed growing in a pot which you bring home. Occasionally, plants are “field grown”, dug and potted, prior to sale, but typically the plant has spend most of its short life in this same pot.
When you get container grown plants home, they are planted by digging a hole the size of the pot, removing the plant from the pot, making sure that the top of the soil of the plant’s root ball is level with the top of the surrounding soil, and then water well. It could not be any easier, or at least so it seems.
One of the most common problems with a containerized plant is getting a root-bound plant. When a plant has lived a long time in the same pot, the roots may have started to encircle the pot. If this plant is planted like this, the roots will continue to follow the same circle and the result will be a dense mound of roots which has completely displaced available soil. Soil is required for roots to take up nutrients, oxygen, and water.
Compared to a “bare root” grown plant, which roots have been fanned out and are growing into the surrounding soil, a root-bound containerized plant will continue to grow in a circle and soon strangle itself.
Ideally, the gardener should remove the plant from the pot at the nursery before purchase and inspect the roots. The root ball should hold together without the soil falling apart. The roots should be visible but the root ball consist of primarily soil with some white roots showing. If there is no visible soil; the root ball is a big mass of roots, as in the above picture; the plant is root bound and you are better off buying another plant.
Planting Root-bound Plants
Sometimes, however, we all end up buying a root-bound plant. When this happens, they can be planted successfully provided the roots are teased apart, or the circling pattern disrupted so they no longer grow in a circle.
One way to plant root-bound plants is to gently tease the roots apart with your hands first. Simply breaking the root ball gently and pointing the roots in an outwards direction is often enough.
Sometimes, the root ball can be so dense, however, that this is simply not possible. Watering the root ball and washing away the soil will then often loosen the roots sufficiently to allow disentangling of the roots.
Some plants, like this Rudbeckia fulgida (Black-eyed Susan), may create such dense root balls that breaking apart with your hands is very difficult, and watering won’t help either. In this case, you can use garden scissors and cut several vertical slits into the root ball. With your hands, you can then gently point the bottom edges of the root ball outwards.
Most perennial plants do well with root pruning. These plants will produce new vigorous branching roots if the old roots are severed. With these, I like to saw off the bottom of severely root-bound plants before planting. Scarifying the sides of the root-ball with scissors is still a good idea.
Not all plants do well with root pruning, however. Some plants, like lilies for example, prefer not to have their roots disturbed or damaged. Read the tags carefully. It pays to ask.
Once the root-ball has been scarified or loosened, planting should be done following these guidelines:
- Plants usually establish best if planted in loose aerated soil. Break up soil in an area twice as wide and one and a half times as deep as the root ball.
- Most perennials prefer a good organic soil. All types of soil can be improved by mixing the native soil with a bit of compost.
- Loosen the soil at the bottom of the hole, and then firm gently. Place the plant in the hole making sure that the top of root-ball is level with or ideally slightly above ground level
- Backfill with amended soil around the sides of the plant. It is usually easiest to fill the cavities on the outside of the root-ball with some soil and then water it in. Add some more soil and repeat until no more soil will fit on the side of the plant.
- Water the plant well initially by flooding the plant. Then let the water drain and repeat. For the next few weeks, until the plant grows new roots, you should water more frequently than you otherwise would with established plants. Even so-called drought tolerant plants need extra water until they are established. A deep soaking minimum twice per week is recommended. If you are planting during very hot, sunny times of the year, water daily to begin with.
The planting advice above applies to bare-root and container-grown plants alike. If you buy container grown-plants and plan on growing them in pots on the patio, for example, make sure buy a new planter at least 2-3 times the size of the original pot. E.g. a 6” pot should ideally be planted in a one gallon container. A gallon perennial should be housed in a container no smaller than 3 – 5 gallons.