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How to create and maintain a shade garden

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Hosta.
Photo: Jardin botanique de Montréal (Lise Servant)  
Hosta

Evaluate the amount of shade of your garden

To obtain a beautiful shaded garden, start by figuring out how deep your shade is.

It may be light, filtered shade cast by a tree with an open crown, dense shade under a conifer or something in between. You should be able to recognize your garden from one of the three descriptions below.

The list of suggested plants at the end of this leaflet also indicates which type of shade each species prefers.

  • Light shade

Plants receive a few hours of sunlight during the course of the day. This type of shade is typically cast by trees with an open crown, like honey-locusts. Light shade is ideal for most of the plants in the list.

  • Medium shade

Plants get little direct sunlight, but plenty of reflected light. These conditions are found near a north-facing wall. Not all plants in the list tolerate medium shade, although many of them do.

  • Dense shade

Plants receive only a little reflected light, and no direct sunlight. This type of shade is found under trees with low branches and dense crowns, such as Norway spruces. The combination of a north-facing wall and another element such as a tree creates essentially the same conditions. Few plants do well with so little light.

Evaluate the disadvantages of your site

Shade from a tree or an artificial structure is not the only thing that can restrict plants' growth.

For instance, a garden in front of a north-facing building is not only in shade for most of the day, but also exposed to the prevailing winds. Plants that do not have adequate snow coverage in winter are particularly vulnerable to frost heave.

There are other problems involved in gardening in the shade of large trees. The roots of fast-growing trees such as willows, poplars, silver maples and Norway maples absorb much of the water and nutrients that other plants require.

Moreover, the ground under conifers is dry and acidic and gets little snow in winter to protect it.

Optimize growing conditions

Of course, it is best to choose plants that are suited to the different sites in your yard. You can improve growing conditions, though, by improving the soil and pruning trees.

Amending the soil

Most shade plants prefer slightly acidic soil with lots of organic matter. It is a good idea to improve your soil by working in 5 to 10 cm of compost.

Whenever you add new soil, use a mixture of equal parts garden loam, potting soil and peat moss.

You can also build raised beds to solve drainage problems. In extreme cases, you may wish to add an underground drainage system.

Pruning of trees

Finally, you can decrease the amount of shade by carefully pruning a tree. Sometimes merely removing a few low-growing branches will allow more light through. If this is not enough, you may wish to thin the crown of the tree. It is best to proceed as follows:

  • remove any dead, diseased or dangerous branches;
  • remove any branches growing vertically or in an odd direction that will spoil the tree's appearance;
  • trim any primary or secondary branches that are growing too close together;
  • never remove more than 20% of a tree's branches at any one time.

Under a tree

Establishing a flower bed under a tree requires some precautions. In order to protect the roots, avoid working the soil too deep near the trunk and under the branches. Adding a slight layer of soil (less than 15 cm) will cause no harm if one takes care not to cover the base of the trunk.

Choose species with a shallow root system, preferably young plants that will adapt faster than mature ones.

If the soil is compact and acidic, plant mosses or spread a decorative mulch.

Maintenance of the shaded garden

Most shade plants prefer moist soil. Mulching is a good way to maintain lots of organic material in the soil.

Adding 4 to 6 cm of compost in spring will help to retain moisture, keep down weeds and increase the proportion of organic matter in the soil.

For native plants, it is enough to add compost once a year, because overly fertile soil will adversely affect their natural growth.

More demanding plants will benefit from a springtime application of fertilizer that will nourish them for 2 or 3 months.

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