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Know Your Landscape
Your Flowers’ Growing Site
Each flower planting site in you landscape makes a good home for specific plants once you recognize how they differ.
A shady location is ideal for low-light plants such as hydrangea, while a sun-drenched brick planter is perfect for annuals such as primrose that flower best if they receive eight full hours of sun each day.
Let’s dive a bit deeper into recognizing the niches your yard contains that will make it possible for you to grow many different kinds of beautiful flowers.
Growing Days
The way the earth’s axis is tilted or inclined combines with its elliptical orbit around the sun to favor first one hemisphere with long days of sunlight, then the other.
Give it a moment’s thought. We all notice the short days of winter and long days of summer, but have you seen how shadows change throughout the year?
Depending on where your garden is located on the earth—its latitude—shadows will cover the least area of your garden on the summer equinox. The sun will be nearly overhead.
The opposite is true for the winter equinox; the sun at noon strikes your garden at an angle, and the sun is much lower in the sky.
One must thing ahead to summer sun conditions when you plant flowers in early spring.
Experienced gardeners recognize these seasonal changes. They know shade-loving plants will need protection from hot, overhead summer sunlight.
Their sun-loving plants will flower nonstop when planted next to walls that face the sun (either south facing in the northern hemisphere, or north facing in the southern hemisphere).
Look at your yard and landscape at noon, noting where shadows fall. Imagine a low sun casting shadows across your yard in winter, and areas with a clear view of the sky that will have strong sun in summer.
These astronomic facts predict the length of your garden season, and the number of good growing days between the last frost of winter or spring and the first frost of autumn or winter.
You’ll see this gardening-season information in the chart below for the United States, shown for each U.S.D.A. Plant Hardiness Zone [see: Plant Hardiness and Climate to identify your own hardiness zone].
Frost-free and heat periods vary within each zone, so the growing season may be shifted slightly from year to year or by geographic location in the zone. Soil temperatures may also vary.
In some years, soils fail to warm sufficiently for planting due to cloud cover, cooling rains, or low air temperatures.
To guide you on when to start seeds indoors or set out transplants, rely on your nearby university’s agricultural extension office or the experienced staff of your garden center.
Precipitation, Watering, and Flowers
While the amount and intensity of sunlight and shade are very important to flowering plants, every gardener knows instinctively that the presence of sufficient moisture is also necessary for their healthy growth and flowering [see: Needs of Flowering Plants].
This is particularly true during times of drying winds, drought, or low soil temperatures. Plants need ample water to grow, retain vigor, and remain healthy. Plan to deliver a volume of water to your flowers of between 1 in. (25 mm) a week and 1/2-in. (12-mm) daily.
Natural Precipitation and Humidity
Certain areas of the country are blessed with ample rainfall throughout the growing season. Others have either sometimes-dry conditions or are naturally arid.
If your home and garden site have regular periods of time when rainfall is sparse or absent, plan ahead for irrigation of your flowers either with hoses, watering cans, or an automated in-ground irrigation system.
Humidity is another factor. Humidity is nothing more than airborne water vapor—the stuff of evaporating steam, clouds, and fog.
Humidity affects flower growth by limiting the amount of moisture they lose during transpiration, through pores in their leaves. High humidity helps slow or prevent dehydration, wilting, and collapse.
Another reality of high humidity, however, is that it causes dew formation during cool evenings and nighttime hours.
While this dew provides some of the water plants need, it has a notable downside: fungal and bacterial disease.
Moist conditions—especially those coupled with cool temperatures—help mildew and other plant killers become established in your flower garden. Always space plants properly if your site is in a humid location.
Temperature, Heat and Flowers
When you review the locations in your landscape, remember three key measures of temperature and plan around them.
They are:
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- Minimum temperatures for tender and half-hardy flowering plants
- Average or ideal growing temperatures
- Maximum temperatures
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Of these numbers, the first—minimum temperatures—determines when you will plant your flowers and summer bulbs in spring.
The second—average growing temperature—is the most important of the three for helping your plants’ health and beauty. It has another function as well–the length in days when your garden’s temperature is ideal for growth and flowering.
The last—maximum temperatures—only comes into play for hot-summer climates, or for container plants in sunny locations.
Heat zones are useful for determining whether a flowering plant species will receive sufficient heat to grow, mature, flower, and fruit. They’re also very helpful for judging whether your site will require protection from excessive sun, especially in U.S.D.A. Plant Hardiness Zones 8–11.
The American Horticultural Society Heat Zone Map shows the United States, divided into 12 regional zones. Each zone is based on the average number of days each year in which its temperature exceeded 86°F (30°C). That’s the temperature point at which damage begins to occur in cellular plant tissue and proteins.
Remember, long-term averages are sometimes misleading. In any given year, the number of hot days may vary up or down by 20 percent or more.
Some plant providers “heat-rate” their plants using the zone map. Use it to guide your selection, planting, and care of your flowering plants and to gauge the needs for plant protection from cold or heat in your own landscape.
While evaluating heat and cold in your garden, remember to note prevailing winds. Hot temperatures combined with drying winds are especially difficult for many flowering plants.