Perennial Planting Guide

Tips for planting, storing perennials prior to planting, selecting digging tools, and mulching.


Preparation

The hardest part of planning your perennial garden is definitely the preparation work. Planting even a large border takes a small fraction of time compared with clearing vegetation and blending amendments into soil.

Before planting, transfer your garden design from paper to the planting bed. For each perennial, you'll need to know the mature size. If your perennials are in pots with plant tags, look for that information on the tag. For bare-root perennials or starts obtained from neighbors or friends, research mature size.

Arrange your perennials in the garden, starting at one point and working outward. Place the plants slowly and carefully, situating them with the correct spacing for their mature size. You might want to let the potted perennials sit on the bed for a few days to view the design from several angles (inside and out) and confirm that you're satisfied with it.

The Best Time to Plant

Aim to plant perennials at a time of year when they'll be able to sink roots with the least amount of stress. In cold climates, planting in late spring or early summer provides perennials an entire season to grow before winter cold arrives. Fall is an ideal planting time in mild regions, where winter brings moist soil and cool air without freezing temperatures. For climates with clearly defined wet and dry seasons, plant perennials at the start of the rainy season and allow rainfall to irrigate the plants.

Mulch

New perennial beds need a layer of mulch to maintain soil moisture and suppress weeds. Adding mulch after planting works well when you're dealing with large perennials -- quart or gallon size. For small and bareroot perennials, it's often easier to mulch the bed before planting. To plant, simply pull back mulch and dig a planting hole.

Mulch quality and type vary immensely. You don't have to pay top dollar to get the best mulch product; you can find inexpensive sources of quality mulch. Many communities gather and compost yard waste and offer it to gardeners at little or no cost.

Read more about mulching.

Perennial Storage

When delays prevent planting, give your perennials attentive care to keep them healthy.

  • One week or less -- If you'll plant in less than a week, place shade or sun perennials in a shaded spot, arranging so air can freely circulate between plants. Water when the soil is dry. On windy days, check the soil twice; water as needed.
  • More than a week -- If you won't plant for a week or more, treat shade perennials as above. For sun-lovers, give them a spot that receives at least four hours of sun daily. Water when soil is dry.

Start Digging

Tucking plants into beds requires some attention to detail, but mostly it's an easy, approachable task. Dig a hole that's no deeper than the height of the root ball and a few inches wider than the container. Remove any rocks you unearth while digging. With a bare-root perennial, form a mound in the base of the planting hole to hold the crown and allow roots to spread out and down.

Choosing Planting Tools

Tackle perennial planting with a variety of digging tools. Specialized tools suited to specific tasks make quick work of planting, but you can manage your garden with a few key implements. A digging spade or round-point spade creates a sharp, straight bed edging. It's also useful for digging holes for large perennials. A short-handle shovel, sometimes sold as a contractor's shovel, works well for digging small holes. The short handle is easy to manage while on your knees, which makes it handy for planting.

A transplanting spade has a long, narrow blade that fits neatly between established perennials. It's the digging tool of choice when you're working in an existing planting bed, maneuvering and digging around plants. For small perennials in 2- or 4-inch pots, a hand trowel or hoe speeds up planting, especially when soil is loose and easy to dig.

Pots, Roots, and Crowns

When dealing with container perennials, water plants thoroughly before planting. To remove plants from pots, invert the container with one hand splayed over the soil and cradling the stems. If the plant doesn't slide out easily, lay the container on the ground and roll it, pressing down with your hands using some force. You can also step on the pot, but use light pressure to avoid damaging the plant.

After removing the plant from the pot, if roots blanket the outside of the soil, tease some free or slice about 1/2 inch into the root ball at several points. The idea is to loosen and free roots to branch into surrounding soil after planting. If you don't loosen roots, they'll tend to circle inside the planting hole, which will stunt top growth.

Before planting, brush soil away from around the base of the stems so you can see the crown. This will help you place the plant at the correct planting depth.

Remove a biodegradable pot before planting as long as roots aren't poking through the pot and the pot isn't decaying. A dry, intact biodegradable pot can restrain roots after planting, preventing them from invading surrounding soil.

Planting Depth

Most perennials flourish when their crowns are planted at the same depth as in the growing container. Test planting depth by laying a tool handle across the planting hole with the perennial placed at the proposed planting depth in the hole. Adjust the soil in the planting hole accordingly. When the crown is even with the tool handle, the plant is at the proper depth. Exceptions to the ground-level planting rule include these:

  • Above-grade. Perennials prone to rot grow better when their crowns are slightly above soil level. These include daylily, lady's mantle, lamb's-ears, and bearded iris.
  • Shallow depth. Perennials that crave moisture thrive when their crowns are 1–2 inches below grade. Examples, as well as how deep to plant, are bee balm (1 inch), bugbane (2 inches), hosta (1 inch), and peony (1 inch deep in warm climates, 2–3 inches deep in cold Zones).
  • Deep planting. Perennials with tuberous or bulbous roots need deeper planting -- about 4 inches below the soil surface. Examples include crocosmia, ornamental allium, and variegated solomon's seal.

How to Plant Container-Grown Perennials

1. Dig

Dig a generous hole. For 4-inch or smaller pots, dig with a trowel. For larger pots, use a spade. In old beds where the soil hasn't been worked in a while, make the planting hole one to two times wider than the nursery pot but no deeper. Dig so the sides of the hole slope toward the center of the bottom. In well-prepared beds, dig the hole as wide and deep as the pot.

2. Check the Depth

Check the depth of the hole by setting the pot into it. Make the plant crown level with the surrounding soil. Planting too deep invites stem and crown rot; planting too shallow might retard plant growth. Check the level by laying the handle of your spade, a ruler, or other straight object over the hole. The top of the container soil should be even with the bottom of the handle.

3. Remove the Plant

Take the plant out of the pot by flipping it over, keeping one hand stretched over the soil around the plant. Tap the pot with your other hand until the plant is free of the container. If a plant won't come out, roll the pot back and forth on the ground while firmly pressing on it with your hands or your foot.

4. Tease Roots Apart

Tease apart any pot-bound roots encircling the root ball. Or make shallow slices around the root ball with a sharp knife, cutting from the bottom to halfway up the root ball.

5. Set the Plant

Set the plant into the hole, evenly spreading the loosened roots. Recheck the planting depth and adjust the depth of the hole so the plant's crown is at the right level.

6. Backfill

Backfill the hole halfway, firming the soil with your hands, then fill the hole with water to settle the soil. When the water has been absorbed, finish backfilling the hole; firm the soil and water again. Use a gentle spray, such as from a water breaker or fan-spray sprinkler, to avoid splashing soil out of the hole.

How to Plant Bare-Root Perennials

1. Check the Roots

Bare-root plants have no soil around their roots. Nurseries often wrap the roots in moist sphagnum peat moss before shipping to prevent drying while the plants are en route. Remove the moss before planting.

2. Trim

Trim any dead or broken roots. Try to keep as many roots intact as you can. The bigger and healthier the root system at planting, the faster a plant will take off when growth begins in spring.

3. Soak Roots

Fill a bucket with water and soak the roots to rehydrate them. Leave them in the bucket for at least one hour and no more than two hours. Adding a root starter to the water is beneficial.

4. Dig

Dig a hole as wide as the spread-out roots and as deep as the roots reach. You can do this while the plant soaks or just before planting.

5. Form Mound

At the center of the hole, form a mound of soil to hold the plant at the right depth and help anchor it while you fill the hole. Scrape the dirt at the bottom of the hole into a high enough pile that the crown or eyes (buds on the roots) sit at the soil surface.

6. Remove from Water

Take the plant out of the bucket just before planting it.

7. Set

Set the plant on the mound and evenly spread its roots over the soil. Backfill the soil halfway, then fill the hole with water.

8. Finish

After the water has been absorbed, finish backfilling the hole. Firm the soil and water again. Move the mulch back around the plant or add a layer. Thoroughly water again and keep the soil moist until the plant becomes established.

Post-Planting Care

After planting, place mulch around perennials, covering any exposed soil. If you mulched before planting, replace mulch around plants. Water thoroughly, soaking the top 8 inches of soil. Dig into soil away from plants to determine saturation depth. Watering settles soil and removes air pockets. If water starts to run off before soil is adequately soaked, stop for 30–45 minutes before resuming irrigation.

New perennials need evenly moist soil to root and establish. Typically 1 inch of water per week, delivered through rainfall or watering, is sufficient. Pull back mulch and check soil moisture 3–4 inches deep to determine whether you need to water. Established perennial gardens need about 1/2 inch of water per week. Moisture-craving plants need more; drought-tolerant plants need less.

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