Those beautiful gardens you admire in your neighborhood and magazines don’t happen by chance. A lot of planning goes into planting a garden. Additionally, it takes a lot of labor and money, so money, so here are some tips on how you can avoid being disappointed when plants you purchased fail to thrive or die. Sadly, many garden centers often carry plants and cultivars that are not appropriate for local gardens. You cannot rely on their selection to steer you in the right direction. This is why it is so important to understand all the variables involved in selecting a plant that will thrive in your yard. Today, we are going to look at how to select plants for your garden.
The first (and often only) thing people look at when buying a plant is the cold hardiness zone.
For those of you who are not aware of what a cold hardiness zone is, the USDA tracks low temperatures and makes a map of the United States. The country is divided into zones based on the low temperatures. If you don’t know the zone you live in, you can use your zip code to look up your zone here. It is important to look at the zone range that a plant will survive in, not just the cold hardiness.
Cold hardiness zone is important, because plants are rated based on what zone they can survive in. Each plant has a minimum temperature that will kill it. If you plant a plant that cannot survive your wintertime temperatures it will die. Therefore, hardiness zone is an excellent place to start when considering a new plant.
Hardiness zone listings on plants can also indicate how far south a plant can be grown. The upper heat tolerance is also an important factor in plant selection. If for example a plant says that it grows in zone 4-7, that implies that it likely will not grow, or perform well in zones 8-11 even though it clearly won’t freeze to death in those areas. Why it won’t grow in the warmer zones can be more complicated.
Hardiness zone is not nearly the whole picture
While the cold hardiness zone tracks the low temperature, it does not take into account any other variables. These variables include things like heat days, heat tolerance, and chilling requirements. There might not be just 1 reason why a plant won’t thrive in higher hardiness zone than recommended.
Information on how much heat a plant needs or will tolerate is less widely published than the hardiness zone. However, the American Horticultural Society puts out a heat zone map similar to the USDA cold hardiness zone map. You can look at it and get an idea of how hot your area is. Then when you are looking at plants, you can do some educated guessing.
Before purchasing plants, consider where they are native to, and what kind of environment the description says that they like. Often, plant catalogs may say something like ‘prefers plenty of summer heat’ or ‘doesn’t tolerate heat and humidity’ or ‘doesn’t usually ripen in our climate’. This combined with the plant’s listed hardiness zones and your heat zone gives you some valuable clues as to whether the plant might do well in your climate.
A good example of how hardiness zones are not all equal would be zone 8 in Washington state and zone 8 in Georgia. Despite having very similar wintertime lows, they are two very, very different climates. Plants that thrive in Georgia might fail to grow in Washington and vice versa.
Why? Because the number of heat days is drastically different.
Plants that thrive in a cool mild climate may burn up in the hot, humid Georgia summer. Other plants, may never fruit in Washington because there is not enough heat to mature the fruit.
On the other end of the season, many plants require a certain amount of chilling to break dormancy or fruit. If they do not receive the required amount of chilling they may fail to grow, or they may fail to fruit. This obviously could be very frustrating.
Chilling hours are defined as when the temperature is below about 45 degrees and above 35 degree. Temperatures above and below this range do not count. You can find maps showing the average number of chilling hours throughout the country.
When you are looking at fruit crops, you often will see somewhere in the description that they require a certain amount of chilling hours. Ornamental plants don’t often list chilling hours, but, if you are planting them outside of their recommended hardiness zones, you can expect that you might have trouble. For example, due to lack of chilling, you can’t grow daffodils as perennials in Florida.
Growing season length should also be considered
Growing season length can be important to consider, particularly if you are looking to ripen a crop. Sometimes a plant may be able to grow in an area without a problem, but may not be able to successfully ripen a crop. Growing season length can limit not only perennial plants, but also annual flowers and vegetables.
You can determine the length of your growing season by counting the number of days between your average first and last frost date. This needs to be considered alongside how much heat your area has.
Though they aren’t often listed on anything except annuals, all plants have a certain requirement for ‘growing degree days’. This is correlated to the ‘days to maturity’ that you see on seed packets. Unlike us, plants do not measure days in calendar days. Rather they measure in the amount of hours temperatures were within a suitable range for growing.
Days where temperatures are too low or too high don’t count toward growing degree days.
Because plants have different optimum temperatures for growth, what counts as a growing degree day varies. Too cold for one plant might be perfect growing weather for a different one.
Going back to our earlier example of Washington vs Georgia, you will find that despite both locations being hardiness zone 8 with the same first and last frost dates, you can very successfully grow muscadine grapes in Georgia, and you cannot get fruit off them in Washington. This is due to the difference in the number of growing degree days. Washington with its cool summers doesn’t have many. Georgia with its blazing hot summers has a lot of them.
If you are concerned that you might not have enough growing degree days for a particular plant, a quick internet search can likely tell you the requirements for the plant. It will also tell you how to easily calculate the average number of growing degree days for your location. However, under most circumstances, this is not really necessary to do. A knowledge of what they are and why they are important is enough for most gardeners.
The last things you should consider are your climate type and insect and disease pressure
Different areas of the country have very different climates. Here we are referring more to humid/rainy vs dry rather than temperatures. This is important to consider because it is futile to try to grow a desert plant in a swampy climate, or a tender, fragile plant that needs high humidity in a dry climate. Not only for obvious reasons like that a cactus would rot if planted somewhere it rains every other day, but also for less obvious reasons.
Trying to grow a plant in the wrong climate stresses the plants and makes them more susceptible to pest and disease damage. Some plants are unable to withstand pest and disease pressures in climates outside of what they prefer. This is probably most often a problem when moving plants to a hot humid climate where they may succumb to diseases that they were unbothered by in a dryer climate.
Some plants are just not cut out for certain climates and should be avoided.
Other plants have been bred to provide varieties suitable for planting in various climates. However, if you plant a variety that is not suitable for your climate, the plant will fail to perform well.
Pears are a good example of this. Bartlett pears grow amazingly well in Washington state, but they will die from fireblight almost immediately if planted in Georgia. However, there are other pair varieties immune to fireblight that will thrive in Georgia.
This is why you should always do your due diligence before purchasing a plant. Oftentimes gardeners fail, not because they are trying to grow a species that isn’t suitable for their climate, but rather because they are growing a cultivar not suited to their climate.
It is important to keep in mind that commercial growers are using many pesticides and fungicides to keep plants and fruit looking perfect. These commercially grown varieties are rarely well suited to homeowners. However, they are often sold at garden centers because the names are familiar to people. Also, plants seen at garden centers are often grown elsewhere and shipped in, so just because they look good there in the nursery doesn’t a guarantee they will do well in your yard.
If in doubt check with an extension agent before purchasing a plant
If you have any questions about whether you should select a certain plant or variety for your yard, it is always an excellent idea to check with your local extension agent. They will be familiar with your local climate, and any unique pest or disease pressures you will be facing. They should be able to recommend suitable plants that will fit well with both your expectations and your climate.
We hope that this helps you have a successful gardening season this year!
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