An Ode to Plant Tags

What do the various things on a plant tag mean? And how does it affect my plant choices?

Accurate plant tags can save you time and money.

Examining the tag will tell you:
• its plant hardiness zone
• how much sun it needs
• its watering requirements
• its mature height and width

Plant Hardiness Zones
What’s the big fuss about plant hardiness zones? It’s a big deal if you are buying perennials, shrubs or trees, plants that you want to last more than a season.

Generally, the lower number, the hardier the plant. If you live in zone 5 area, buy plants with 5 or lower number rating.

If you have a windy, cold north-west facing garden, err on the side of caution and buy plants that could survive in plant zone colder (in this example zone 4).

Plants in containers or on rooftops are more likely to survive if they are two zones hardier (in this example zone 3).

Most tags feature USDA plant hardiness zones, although occasionally a nursery may use the Canadian plant hardiness zones (check with the garden centre staff). If there isn’t a plant hardiness zone on the tag, the plant is likely an annual or not hardy in your region.

If you live in the USA, use the National gardening Association’s plant hardiness zone finder ( Insert your zipcode and bingo out comes your hardiness zone.

In Canada, Landscape Ontario automatically gives you a reading without inserting your postal code. HGTV also has a great interactive map. (


Sunlight requirements
In order to thrive, plants need sunlight. Of course different plants require different amounts of sunlight to grow. Before rushing off and buying all the pretty floral full sun plants, check to see how much direct sunlight your own garden gets at the height of summer (usually July in the northern hemisphere). Remember to observe direct sunlight in different parts of the garden; it might be different.

Observation is the time-honoured method of determining hours of direct sunlight. But if you don’t have the time to watch your garden all day, or lose count or focus, get an electronic gadget like the Sunlight Calculator, which measures hours of direct sunlight. (You can order a Sunlight Calculator from Lee Valley Tools (, click on gardening, then weather & time).

A circle is commonly used to symbolize amount of direct sunlight each type of plant needs to grow well.

  • A clear circle: full sun (6 or more hours of direct sunlight)
  •  A half-filled circle: partial sun (less than 6 and more than 4 hours of direct sunlight)
  • A half-filled circle: partial shade (less than 4 hours and more than 1.5 hours of direct sunlight)
  • Fully filled circle: shade (less than 1.5 direct sunlight hours)

Sunlight requirements aren’t that flexible. If it is a full sun plant, it won’t do well in a full shade location. And a woodland plant with low light requirements will sizzle in hot sunny meadow. So, read the label, and buy only the plants that suit your garden’s sunlight conditions.

Watering requirements
With water shortages and water conservation forefront in government’s efforts, drought tolerant plants have risen to superstar status. Unfortunately only a few of the plant tags have water requirements.

A stylized raindrop represents water:

    • One drop = drought tolerant
    •  Two drops = middle of the road


    • Three drops = water hog



A word of caution
With all the fuss about drought tolerance, it’s easy to lose our heads and select only drought tolerant plants. But they are not always the right plant for your location. Bogs, sites along a stream or at the foot of a slope need plants that thrive in moist soil.

And just because it is drought tolerant doesn’t mean you never water the plant! After planting the drought tolerant wonder, water it until it becomes established. Sometimes it takes two or three summers. Even when it’s established, the plant may still need water during prolonged drought.


Written by Cristina da Silva
Tuesday, January 26, 2010 in Plants & Soils

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