Monday, October 3, 2011

Defining Shade

In the Pacific NW, shade is something gardeners must learn to love. I’m from Texas and I can tell you that in other parts of the country, shade is something devoutly to be wished. People go to unbelievable lengths to produce a bit of shade to make their summer more endurable. Even in the cloudy and brisk climate of maritime Washington, a shade garden can be an elegant and serene counterpoint to a rowdy summer border. Aug 189

Shade is a multifaceted condition. Typically, shade describes an area that receives less than 4 hours of direct sun a day. A full shade plant prefers less than 4 hours of sun; you must consider not only the length of time in the sun, but also the position of the sun. A full shade plant that receives only 2 hours of direct sun-but in the middle of the day-will not thrive and may die. Learning how the sun moves across your site will help you to estimate what type of shade you have.

Aug 155Bright shade areas may receive dappled shade all day; or direct morning or late afternoon sun; or they may be bright, but not sunny. A wide variety of plants will thrive in these conditions.

Frequently, deciduous trees produce a mixture of sun and shade referred to as dappled shade. The shade area created will be larger than the tree canopy because of the movement of the sun. Usually, you will find full days of sun filtered through the leaves, but little to no direct sun. Woodland plants are ideal for these situations Aug 160

Plants that are labeled “Full shade” will not grow in the dark-all plants require some light. Full shade plants will do well in dappled shade conditions and may even grow in reflected light from a light colored wall or fence. I have an area on the side of my house that receives only reflected light for a majority of the year where I am able to grow many varieties of plants.

Dense shade can be defined as areas that get limited light-too dark to be considered dappled shade-and no direct sunlight. Frequently, these areas may have complicating factors such as surface roots and evergreen canopies. There are few plants that will bloom in such IMG_0016conditions, but you can rely on full shade shrubs and foliage plants. Variegated plants can provide variety and light up the dark space. Because tree roots compete for the moisture and nutrients, you may not be able to plant densely. Woodland flowers, sometimes known as ephemerals because they disappear after blooming, can provide delightful color. These plants emerge and bloom in spring before the trees leaf out completely.

Sometimes dense shade can be improved. Trim off the lower branches to allow more light to penetrate under the canopy. Substitute an openwork barrier for a solid fence. Select companion plants that will tolerate dry shade. Consider a sitting area, hammock, water feature or garden art in an area that doesn’t support as many plants as you would like.

Shallow rooted trees make planting anything difficult. Creating a raised bed is tempting, but will likely weaken and possibly kill the tree by burying the roots too deeply. Tree roots are naturally quite shallow growing. When root systems are buried, less soil oxygen and water is available.  An oxygen level of 25% of the soil volume is considered good for root development. At a 5% oxygen level growth stops, and at 2% roots decline and die1. If you are able to build a bed that doesn’t smother the roots, the roots will eventually grow up into the new soil, duplicating the existing problem you are trying to solve.

If you have evergreens with branches only a foot or two above the ground you should probably forgo planting and mulch for weed prevention. Use no more than 2-4” of mulch; more than that will have the same deleterious effect as too much soil piled on the roots.

1 Ohio Department of Natural Resources, Division of Forestry

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