A typical distinction when growing flowers is whether they should planted in sun or shade. Offhand, this sounds like a clearly defined choice: sun or shade; one of two options; no in between.
In reality shade is a much more diffuse concept.
First, there is no such thing as “one-size fits all” shade plants. Plants have varying degree of shade tolerance ranging from those which grow best in mostly sun to those which do well even in a dark corner of the yard. Just because a catalog groups several plants as “shade plants” it does not mean they perform equally well under all circumstances. Some plants will grow adequately in a fair amount of shade, but may need staking to avoid leaning. Some plants prefer protection from hot direct sun to avoid dehydrating. Other plants refuse to flower properly without direct sun for a substantial part of the day.
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Shade is not a definitive concept.
Shade can be light or dark depending on how much sun gets through to the leaves of the plants. A mesh screen or the canopy of a tall tree may permit varying degrees of sunlight through. The garden may receive direct, unobstructed, sunlight for part of the day, but be shaded by buildings, fences, or trees during other times of the day. A flowerbed may be in full sun in spring before the trees leaf out, but be covered by heavy shade in autumn. A tall oak tree with a loose canopy may allow more sunlight to reach a plant compared to a low growing maple with a dense canopy.
Shade tolerance vary by location
Sunlight intensity is typically weaker in the morning and in the late evening and much stronger during midday and the early afternoon. A shade tolerant plant can thus be planted in morning sun, but afternoon shade, whereas a less shade tolerant plant could receive morning shade and still thrive. Sunlight is also stronger the further south you go. Plants which require full shade in the dessert may require full sun in the northern half of USA to perform adequately.
Water and wind matters, too.
To make it even more difficult, shade is sometimes defined by the amount of water reaching the plant. A low growing maple tree may prevent rain from reaching the ground under the canopy, and the surface growing tree roots will compete for water and nutrients. This is also called dry shade. These conditions may not favor the growing of moisture loving species, such as ferns, for example, whereas a north east corner behind a tall fence receiving the same amount of sunlight may work wonderfully because water is available and there is no competition from tree roots. This is also commonly referred to as wet shade, especially in areas where the soil never dries thoroughly due to lack of sunlight and wind.
Breaking down “Shade”
Shade is by definition anything less than full unrestricted sunlight. Sunlight is measured in a number of ways (lux, foot candles, etc).
“Foot candles” is an old but widely used term, with full sunlight at noon in New Jersey reaches approximately 10,000 foot candles. A reading lamp will produce roughly 250 foot candles. The fewest of us will actually bring light meters outside to measure the intensity of our shade, and it probably will not help us greatly either, as most plants do not come with foot candle readings (maybe they should ?).
However, the important thing to recognize is that even if an area is very bright, it may still not receive very much direct light (foot candles). The same goes indoors under lights. Light bulbs may make a room appear very well lit, but in comparison to sunlight, lamps put out very few foot candles.
To determine which kind of “shade” you have, it helps to break down the concept into a number of groups. My choices below are aligned to fit the descriptions you can expect to find in gardening catalogs.
- Full Sun
- Generally, this is plant areas where the sun can reach unrestricted. Besides the intensity, the duration is also important. Generally, plants which receive 6 hours or more direct, unrestricted, sun are said to be in “full sun”. If you are gardening in the northern half of USA, and the direct sun is in the morning (AM) hours, you may want to make this 8 hours
- Light shade or Dappled Shade
- This is better thought as “mostly sun”. In these areas, plants will receives 4-6 hours of direct sun (6-8 hours AM sun in the north). Light shade can also be full day screened sun, e.g. such as a mesh screen or a tree canopy which is not too dense. As you can imagine, light shade is a spectrum ranging from almost full sun to almost shade, but generally quite a bit of light reaches these plants still.
- Medium Shade, or just “shade”, is for plants which receive 2-4 hours of direct sun (4-6 hours AM sun in the north). This can include areas behind a fence which is not covered by low hanging branches, and is generally very bright, but still very little direct sunlight reaches the area. It can also be dappled shade, as mentioned above, but at the darker end of the spectrum.
- Deep Shade
- Dark shade is plants which grow in areas where no direct sunlight reaches. Reflected light can still make the area bright, but such light is generally low in foot candles. Deep shade also includes areas under mature trees which receive short periods of direct sun, but less than 2 hours total.
To evaluate a flower bed, you will have to monitor it over a period of time. Write down if it is getting mainly morning or afternoon sun. Is the sunlight filtered through trees, or are shadows cast by walls. How many hours of full unrestricted sun are accumulated? Monitoring the flower bed throughout a whole day is often recommended. Try to do this 3 times per year: in early spring, midsummer, and in fall. You may be surprised by the amount of shade an area get, and how it varies over the growing season.
As mentioned, the well being of plants may vary greatly from situation to situation:
- Geographical location
- Sunlight is a lot stronger in the south, and some plants listed as “full sun” should still have shade for afternoon sun in the warmest areas of the country
- Sun loving plants in the north should be planted in full sun even if they are rated as “likes afternoon shade” which is typically written for courtesy of southern gardeners
- Wet or Dry
- Some plants are very susceptible to foliage disease, such as mildew, if the leaves remain moist. These plants should therefore always be planted in full sun (in the north) to allow the plant to dry in the morning
- Plants planted under the canopy of mature trees, may not receive enough water to support adequate growth. Note that several shade tolerant plants have high moisture requirements.
- Source of Shade
- Shade, when provided by mature trees, is often accompanied by other problems such as competing tree roots for nutrients and water. Compact soils may also be a problem.
- Fences and buildings tend to create well defined blocks of shade. In some cases, a combination of these can block out most of the useful light and make it inhabitable for only the most shade tolerant plants
Note that shade does change. Before trees leaf out in early spring, flower beds can be in full sun allowing you to grow spring flowering bulbs even if you are restricted to shade tolerant plants for the rest of the season. Through out the growing season, the level of shade changes with the position of the sun and the growth of the surrounding plants.
Even among the darkest areas there will always be individual spots, which receive more sun than others. Use this to your advantage. You can for example plant a single sun loving peony in a bed of shade tolerant hostas. This tip is also good if you are trying to grow grass under large trees. Sometimes, defining a small lawn to the areas getting the most sun will give a lot more enjoyment than a bare, poorly performing lawn.
If in doubt, it is always beneficial to go for a slightly more shade tolerant plant. Even the real “shade lovers” are usually only shade tolerant to a certain extend and can usually be grown in quite a bit more sun. Sun loving plants are usually not as forgiving.
Experiment! Annuals can be replanted in new positions next year, and perennials can be moved in spring or fall. Some plants may turn out to do a lot better than you had thought. One year, we planted red annual salvias in full sun in spring. In early autumn they were shaded by mature trees, but they still bloomed better than the begonias in the same spot.
Fertilize less. Plants grown in shade areas generally grow and transpire less. They also consume less fertilizer. If fertilized as their sunny counter parts, they will perform poorly.
Far too many catalogs will overplay the shade tolorance of flowers. If you live in the north, err on the side of planting in more sun than stated (the opposite is true in the south).
Before you buy, however, first get out in the garden, and learn about your shade. Then learn about which plants are suited for your shade. The very last step is the actual buying of plants.
What is your Shade?