Sun, Shade or Perhaps Something in Between

One of the most basic questions on gardening is whether you are looking for a sun or shade plant, or maybe something in between. This simple idea can be difficult to define if you don't understand what constitutes full sun, full shade, and partial sun/shade. This article will go over the basics of sun and shade and how to determine which category different areas should be labeled.

I was just out in my yard looking at half a dozen hostas that are suffering in too much sun. This got me thinking about the Supertunia^® Royal Velvet I tortured with too much shade last year. From there I started thinking how easy it is to put a sun plant where it gets too much shade or a shade plant where it gets too much sun. I think part of the problem is that many people aren't certain just exactly what constitutes full sun or full shade, much less partial sun or shade.

I know a rule of thumb that I learned somewhere, but I was curious about what information was available via books and the internet. Much to my surprise, none of my books defined sun or shade. I also found almost no information on the internet. I was a bit stunned by this lack of information. Although, I suppose my internet search skills might simply not be up to par. Nevertheless, I am here to give you some general guidelines about sun and shade.

The rules of thumb I learned are:

Full Sun is 6 or more hours of direct sun a day

Partial Sun or Partial Shade is 4 to 6 hours of direct sun a day

Full Shade is less than 4 hours of direct sun a day

Rules of thumb are a great place to start but few things are as simple as a rule of thumb makes them seem.

Full sun plants like bright sunny areas. Many full sun plants will be perfectly happy with sun 14 hours a day, every day. Some plants are happy with sun 14 hours a day, unless it gets hot then they like some afternoon shade (when the sun is hottest.) How do you know which sun plants prefer a bit of a heat break? If the plant is noted as being great for early spring it is a good bet that it will be happiest with some afternoon shade. Some plants that fall into this category are Pansies, Violas, Diascia, Nemesia, Osteospermum, and Argyranthemum. Plants that are noted as heat and/or drought tolerant are generally pretty tolerant of even hot afternoon sun. Plants in this category include Rudbeckia (black eyed susan), Echinacea (purple coneflower), Heliopsis, Coreopsis, Angelonia, Phlox, Scaevola, Chrysocephalum etc...

Partial sun and partial shade are probably the most confusing category. The two terms are fairly interchangeable. These plants prefer 4 to 6 hours of sun a day and would be happiest getting their sun mostly in the morning and/or evening with shade through the middle of the day. If a plant is called partial sun the emphasis is on making sure the plant gets at least 4 hours of sun a day. If a plant is called partial shade then greater emphasis is placed on the plant not getting more than 6 hours of direct sun.

You may also see the term Dappled Shade. Dappled shade refers to areas where there is a mixture of sun and shade, generally because a deciduous tree is nearby. Dappled shade is similar to partial shade. Plants in this category are often woodland plants and will do best with little full sun (even morning or evening sun). These plants thrive on full days of sun that has been filtered by trees. Bloodroot, Aquilegia, Wild Ginger, Wild Violets, Jack-in-the-Pulpit, and Meadow Rue are examples of woodland plants.

Full shade plants prefer to get little direct sun. They like less than 4 hours of direct sun a day and prefer morning and evening sun to mid-day sun. Full shade plants should also do outstanding in dappled shade conditions. An area that will be shaded by a fence or wall will need to get several hours of sun in either morning or evening for plants to do well. Full shade does not refer to dark places.  All plants need at least some light.

So what happens to your plants if they aren't placed in the correct exposure? With the help of some photos from my own garden I will give you a few examples of what plants can look like with too little or too much sun. One caveat before you start looking at pictures. I am strictly a point and shoot photographer which means I am adequate, at best. I lack the patience to wait for the right moment to take a photo, thus many a mediocre photo in my portfolio!

First, what happens when a plant gets too much sun? Generally you will see sunburn, light colored foliage, bronzing on the foliage, or brown crispy foliage from too much sun.

The photo on the left shows a Hosta that is getting direct sun from sunrise until about 1 pm when the sun goes behind the house enough to shade it. The crispy and yellowing foliage are pretty classic examples of too much sun. The photo on the right shows a hosta (the same variety, it was here when we bought the house so I'm not certain which one) that is getting little to no direct sun but bright light most of the day. Other than a few insect problems it is doing well. This planting is also an example of underestimating how much sun an area gets. I didn't mean to torture this plant (and the other 5 in similar locations) but I totally underestimated the amount of sun this area gets. The good news is I now know where I can plant the peonies I want.

These two photos show a ColorChoice shrub called Dream Catcher^™ which prefers partial shade. I have these two plants in containers and I am sizing them up to go into the garden in the fall. The photo on the left shows sunburn from too much sun while the photo on the right shows a much happier plant.

You've seen some examples of what plants look like when they get too much sun. When plants get too much shade what you often get is simply lack of vigor and lack of flowering. Plants getting too little sun will often have more insect and disease problems. Healthy plants are much more capable of fighting off potential problems. I have 7 hanging baskets on my wrap around porch. The conditions range from full shade to full sun. For the past two years I have planted monoculture baskets around my porch. I prefer to have all of my baskets match and I was curious how plants would perform in the variable exposure. The plants were all fertilized and watered when needed. The full shade plant generally needs to be watered about half as often as the part sun and sun plants.

The photo on the left (above) shows Diamond Frost^® looking pretty good. If you didn't have the plant on the right, which is larger and more prolifically blooming, it would look pretty good. Both plants are watered when needed and had the same amount of slow release fertilizer applied when I planted. The plant on the left is in a full shade situation and the one on the right gets about 5 hours of sun a day. This proves that Diamond Frost^® will tolerate full shade but will do best in partial to full sun. I planted both baskets with 3 plants in mid May the photo was taken in early August.

Last summer I purposely tortured Supertunia^® Royal Velvet with full shade conditions in addition to keeping it nice and happy where it got about 6 hours of direct sun a day. Both baskets were planted with 3 plants in mid May; the photo was taken in mid July. The hanging basket on the left is pretty sad; it does have some color but is much weaker and developed aphid problems. The plant on the right is happy, really full and flowering like crazy. Supertunias^® are heavy feeders (I call them the teenage boys of the plant world, they have hollow stems) and will do best when fertilized often. I used slow release fertilizer at planting and then used water soluble fertilizer at least once a week.

So how can you avoid torturing your sun plants with too much shade and your shade plants with too much sun? One way is to draw a simple diagram of your garden. Then one day when you have time go out every hour, starting first thing in the morning, and mark which areas have sun or shade. Count the number of hours each area has sun to determine which conditions apply. The angle of the sun will impact how much sunlight each area gets. Northern exposures become much shadier in the winter and southern exposures get much more sun in summer. You may want to check the hours of sun each area receives every few months to get a really good feel for the amount of sunlight each area gets as the seasons change.

If this sounds like too much work, I have seen ads (although I haven't used one yet) for a sunlight calculator. You place the probe (it looks like an old fashioned meat thermometer) in a location first thing in the morning and 12 hours later the device tells you if the location is sun, shade, or something in between. It is available online through Lee Valley and more than likely other locations also.