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How to Select and Plant Perennials


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PLANTING STEPS

(a)  After preparing soil, dig a hole deep enough to hold root ball.
(b)  Remove the pot, break up root ball if root-bound.
(c)  Place root in the hole, fill with water.
(d)  Refill with soil. Root ball should be slightly below soil surface.
(e)  Water a second time.

1.  CHOOSING PERENNIALS

When buying perennials, look for fresh, healthy-looking plants that appear vigorous and ready to grow.  Avoid overgrown, floppy or leggy-looking plants, or any that are small and struggling to stay alive. Certain perennials (especially those with daisy-type flowers) are so vigorous they are often root-bound in the pots; they usually overcome this quickly once planted in your garden.

Any plants that have live insects or foliage diseases should be avoided, since they might start a bigger problem on plants already growing in your garden. The odd bent leaf or broken stem is usually an indication of slight damage during shipping, and this will not generally cause any long term problems. Any moss, liverwort or other weeds in the pot should be picked out and discarded before planting the perennial in your garden.

2.   HARDINESS ZONES

Use this table to help determine which plants are suitable for your winter conditions.  Any plant with your zone number or lower should be suitable.

If you are in doubt be sure to ask your local garden centre staff.

 

 

Minimum Winter Temperature

Zone

ºF

ºC

1

Below -50

Below -46

2

-50 to -40

-46 to -40

3

-40 to -30

-40 to -34

4

-30 to -20

-34 to -29

5

-20 to -10

-29 to -23

6

-10 to    0

-23 to -18

7

0 to   10

-18 to -12

8

10 to  20

-12 to   -7

9

20 to 30

-7 to   -1

10

30 to  40

-1 to    4

 

Use this information as a general guide for selecting suitable plants for your area.  Many other factors affect overwintering of perennials.  Some of these factors include:  reliability and depth of snow, soil moisture levels and site-specific micro-climates.

For more information on Plant Hardiness, visit Plant Zone Hardiness Maps under Gardeners Resources on this site.

For the link to the United States Department of Agriculture new interactive Plant Hardiness Map, click here

For the link to the Agriculture and Agri-Food Canada Plant Hardiness Zone Map, click here

3.  HOLDING THE PLANTS

Although perennials may be held in their containers for a short period of time (say up to three weeks or so), we recommend they be planted as soon as possible to avoid having them accidentally dry out in the pots. The sooner you plant them, the faster they can become established in your garden.

If you must wait to plant them, perennials in pots will be happiest outside, so long as temperatures are above freezing. They may be held in the garage, garden shed, or even in the house overnight, but any longer than a day or two can cause them to stretch and possibly to lose some of their cold tolerance. Regular watering will be necessary, a couple of times a week during cool weather, every day during warm spells. A lightly shaded location will help to keep your perennials evenly moist.

4.  WHEN TO PLANT

Mid to late Spring is the ideal time to plant container-grown perennials. They have a chance to get well established before the heat of summer arrives. Spring is also a good time to divide or transplant many types of perennials that you may have in your garden. Peonies, Iris and Oriental Poppies should not be divided in the spring, but can be planted from containers all season long. Perennials purchased in late winter or very early spring may need special handling, depending on where you live. Avoid putting perennials into the ground while there is still a good chance of hard night frosts. See HOLDING (above) for ideas on how to keep them healthy until planting time.

Summer planting is very successful, so long as plants are not allowed to dry out. Watering is especially important if the weather is hot and dry. Transplanting or dividing perennials already established in your garden is not recommended during the summer, except for Bearded Iris and Oriental Poppies, which should be divided only in July or August.

Fall planting is highly recommended in most regions. Early-blooming varieties will put on a colourful display in spring if planted in the fall. Dividing or moving perennials in the fall is usually very successful. Winter frosts may “heave” fall-planted perennials. Check them in late winter and if any have popped out of the ground, gently press them back in place.

5.  PREPARING THE SOIL

The single most important step to having a healthy, successful perennial garden is properly preparing the soil.

Most perennials grow best in a deep, rich, well-drained soil but check your plant tag for more information.

Dry, sandy soils can be improved by adding plenty of organic matter, such as compost, moistened peat moss or composted manure. Dig the area to a depth of at least 20cm (8”), preferably with a fork or spade.

Heavy clay soils need to be opened by adding plenty of organic matter, along with perlite, coarse sand or grit. A 12-15cm (4-6”) layer of compost, or other organic matter, and 5cm (2”) of grit will greatly improve clay soils.

Few perennials do well in wet, poorly drained soils. If you have a soggy garden area, consider building raised beds or installing tile drainage. If you are not prepared to do this work, you’re best to choose perennials that will do well under waterlogged conditions.

6.  WEEDS

The planting area must be free of perennial weeds, especially spreading types such as Canada Thistle, Bindweed and Couch or Quack Grass. Ask your garden centre which products they recommend for controlling specific weeds. Take fresh samples of the weeds with you for proper identification. Another option is to smother the weeds with black plastic or many layers of newspapers weighed down with bricks or rocks for a period of 3 to 4 months.

Annual weeds or perennial weed seedlings are easily controlled by hand weeding, which needs to be done once a month for the first season. In future years your plants will get larger and do a much better job of shading the soil below, reducing, but not eliminating, the chance of new weeds appearing from seeds.

7.  HOW TO PLANT

Hold the pot upside-down and shake or tap it to loosen the plant roots. If lots of roots are visible, the plant may be rootbound. If so, the root ball must be disturbed to force new, healthy root growth. To do this, take a sharp knife and slice off the bottom ½ inch of roots, then rough up the sides of the rootball with your fingers or the knife tip.

With a spade or trowel, open up a hole deep enough to accommodate the root ball. For best planting results, use the puddling method; fill the hole with water, place the plant upright in the hole and fill in around the roots with soil. Pat the soil to thoroughly mix the soil and the water. This helps to eliminate any air pockets around the roots Be sure the root ball surface is at or just slightly below the garden soil surface. After planting, you may choose to spread a mulch to a depth of 2-5 cm (1-2″), taking care to taper it down towards the plant stems so no mulch is touching them. Water a second time.

8.  WATERING

Water plants immediately after planting and once a week or so for the first two weeks, unless the weather is rainy. Summer plantings may require more frequent watering, especially during periods of drought.

9.  FERTILIZING

Perennials may be fertilized with either a liquid or a slow release granular-type fertilizer. Ask your garden center to recommend a good product. If your soil is fertile and well prepared to begin with, no additional fertilizing should be necessary the first year, although incorporating some bone meal at planting time is often helpful.

Established perennial beds benefit from a yearly spring application of slow release fertilizer or compost.

10.  MAINTAINING YOUR PERENNIALS

Our Heritage Perennials Online Search Engine will help you to locate specific information on each type of perennial in your garden, with tips on special things that may need to be done, such as staking, cutting back and watching for diseases or pests. As well, many books are out there on perennial gardening, and one aimed at your specific region is always a handy thing to have for advice tailored to local conditions.

Here are some general guidelines for maintaining perennials:

  • Prune off any dead tops in late winter or early spring.
  • Remove dead flowers regularly to encourage repeat blooming.
  • Water during drought if possible; early morning watering avoids losing much to evaporation.
  • Clip back scruffy-looking plants to promote fresh, attractive growth. Late spring and early summer perennials often could use a good hard clip after blooming.
  • Control any pests and diseases as soon as noticed, to avoid spreading the problem to other plants.
  • Stake tall plants like Peonies, Delphinium, and Summer Phlox before they reach 2 feet tall, to avoid wind damage later.
  • Divide perennials when the center of the plant begins to die out with age.
Below are some books which contain lots of good information on gardening with perennials.

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