Garden zones, chill hours, & frost dates explained
Check out my video on YouTube that explains what are garden zones and how they affect plant selection.
Knowing your own garden microclimate is key to success. Every garden is different. I highly recommend that you track important weather events in a garden journal. I use a one year planner type of journal to track when the first cold front of the winter season came thru my area, and when the last cold front left in spring. I notate which plants were affected/damaged by the cold, and which were not. After several years, I have a very good grasp of how weather will affect my garden.
Below are some key points about weather that will help you learn your specific microclimate.
USDA Garden Zones - what is my garden zone? How cold will it get?
If you do not know which garden zone you are in, check out this website: www.plantmaps.com. You enter in your zip code and it will provide a lot of useful information.
The difference between for example zone 8 and 9, is 10 degrees. Someone in zone 9 could potentially experience temperatures as low as 25F while someone in zone 8 could get temperatures as low as 15F.
The difference between "A" and "B" designations is just 5F. Someone in zone 9B could see temperatures as low as 25F, while someone in zone 9A could get temperatures down to 20F.
The garden zone data will only tell you what is the lowest degree Fahrenheit that you might experience in your area during any random winter. For my zone 9B garden, it says that I might experience temperatures as low as 25F. I personally have not seen the temperatures go that low, but it is still possible.
This is important to know when selecting fruit trees or other perennials for your garden. When you go to a nursery you will notice that most plant tags will list that particular plant or trees "cold hardiness". This is the lowest temperature the plant can handle before risk of cold damage or even death, will occur. Below are some general examples.
Sour Sop (aka Gunabana and Rollinia Deliciosa) - cold hardiness is on average 40F. That means ideally this tree should be planted in a warm climate where winter temperatures don't get below 40F. I personally have both of these fruit trees in my garden. I know that I will have to cover them to protect from cold damage if temperatures are estimated to get below 40F. When temperatures get 40F and below the trees start to defoliate and drop leaves. When temperatures get into the 30F's, the trees have significant cold damage and lots of limbs die off.
Jaboticaba - most varieties are cold hardy down to 25F. This is a good choice for my garden since my zone has the potential to get down to 25F. I do have a jaboticaba tree in my garden and it never gets damaged by the cold.
Avocados - I have "Brogdon" variety of avocado which is cold hardy down to 24F. I'm located in Orlando Florida. However, someone who is located in northern parts of Florida, zone 8 A/B, will have to select a cultivar that is a little more cold hardy since they could potentially experience temperatures down to 15F. For example, the "Fantastic" avocado cultivar can withstand temperatures down to 15F without any cold protection.
Check out my YouTube video "What is my garden zone? Cold hardiness and how it affects plants": https://youtu.be/s-BKaICOLLw
What are my first and last frost dates? When to start seeds?
If you plan to sow seeds, you must have an idea of your first and last frost dates. Most seed packages will say "sow 6-8 weeks before your last frost date". This means to start the seeds 6-8 weeks before the last frost date that occurs in spring in your area. This also usually means you will be starting the seeds in doors since to protect them from the cold. You will have to know your last frost date so you can back track and calculate the date you should start the seeds. The website www.plantmaps.com will list the average first and lost frost dates for your area. This is an average. It can vary every year. For example, one year my last spring frost came thru on February 8th, while the next year it was March 3rd (meaning we had a longer winter that year).
What is my average monthly high and low temperatures? How to plant according to average temperatures.
All plants have an ideal temperature range that they prefer in order to thrive in your garden. Sometimes it is useful to use this data to get an idea of when to direct sow seeds in your garden. The website www.plantmaps.com has a chart at the bottom that will list the average monthly high and low temperatures in your area. I find this information useful particularly when I am trying to decide on when to transplant anything that is heat sensitive. This includes crops like broccoli and sweet peas. If I transplant them into my garden too early when it is still very hot, it will cause them to bolt (flower instead of producing a head of broccoli), or just stunt their growth. For example, peas thrive in temperatures below 80F. When they experience temperatures +80F, their leaves get fried and die off. The plants are stunted and do not grow. I decide to direct sow seeds for peas in the month where the average highest temperature is below 80F. For me this is the month of November. Therefore, I direct sow all of my pea crops in November. It works, they grow perfectly.
What are cold chill hours? How does it affect fruit tree production? Why is my fruit tree not producing?
Cold chill hours is the required amount of hours at 45F or below, that a fruit tree requires to break its winter dormancy, start flowering, and therefore produce fruit. This affects a wide range of fruit trees such as peaches, plums, apples, nectarines, and blueberries. If you purchased a fruit tree and it has never flowered or produced fruit, I would check its cold chill hours requirement.
To figure out how many cold chill hours your garden gets every winter season, check out this website: www.agroclimate.org.
Lets use my garden as an example. My zone 9B garden received 80 cold chill hours one year, which was a very mild winter. The next year we received 200 chill hours which was a much colder winter. I know that my area can get any where between 80 - 250 cold chill hours. I will have to be careful when selecting fruit trees to ensure my area will provide the amount of chill hours it needs. I have a "Florida Prince" peach tree which only requires 150 chill hours. It produces wonderfully in my garden. The most commonly used peach tree cultivar for commercial production in Georgia is called "Floririch". It requires 700 chill hours. My garden will never give it enough chill hours for it to break winter dormancy. Therefore, the Floririch cultivar is a bad choice for my garden as it requires colder temperatures to break winter dormancy and ultimately fruit.
I highly recommend that you purchase fruit trees from a local nursery because they will carry the cultivars that will produce in your area. If you are going to purchase fruit trees online, make sure you do research to ensure it will get enough cold chill hours.
Another example, (which quite frankly irritates me LOL) are blueberries. I cant tell you how many times I walk into my local big box store and see tons of gorgeous blueberry plants. I take a look thinking I might buy some. I Google the cultivar really quick before I buy it and come to find out its a cultivar that requires way more chill hours than what the entire state (Florida) will even get. The big box stores carry generic cultivars sole all around the USA. Please do not buy fruiting trees/shrubs from big box stores. Go to local backyard or family owned nurseries. Below are some of my personal favorites around Florida. But there are so many more I know I am missing.
Nick's Edibles
https://www.facebook.com/groups/147955578957442
Located in St Cloud FL. Wide variety of fruiting trees specific for Florida. Can find him on Facebook by searching for the Facebook group called "Nicks Edibles". I have bought SO MANY of my fruit trees from him and every single one is thriving.
Stone River Nursery
https://www.facebook.com/stonerivernursery
Can find him on Facebook or Instagram. Located in Orlando Florida. The owner is the expert on everything apples. He grafts special hard to find heirloom apple varieties on rootstock that forces them to require much less chill hours and acclimate better to Florida soil and weather. He carries so many apple varieties, not just the commonly found Anna and Dorsett. I have quite a few apple trees from him.
Luka's Nursery
https://lukasnursery.com/
Orlando Florida. Huge family owned nursery with a large selection. I love their pollinator section. Open to the public.
A Natural Farm
Howie-In-The-Hills
https://www.anaturalfarm.com
Huge selection of fruit trees and plants that do well in Florida. Also hosts educational classes and events.
Alisha's Backyard Nursery
https://www.facebook.com/groups/AlishasBackyardNursery
Located in Orlando FL.
Pokey's Nursery
https://orlandoplantsandtrees.com/pokey-lake-gem-citrus-nursery/
Apopka Florida. Specializes in citrus. I was referred to them by another fruit tree nursery owner who said they simply had the best quality of citrus, and its true.
Pine Island Nursery
https://www.tropicalfruitnursery.com/
Miami Florida. Huge, massive, fruit tree nursery. They have everything. I got my lychee trees from them. Great prices too.
Jene's Tropical
https://www.jenestropicals.com/
Saint Petersburg Florida. Nice selection.
Green Dreams
https://www.greendreamsfl.com
Located in Shady Hill (near Tampa). This guy is famous on YouTube and has tons of tutorials on how to grow fruit trees in Florida. He has a massive nursery. You can order online or pick it up (requires an order minimum). Unfortunately I don't think they allow you to walk thru their nursery. Its not open to the public like that. But he has awesome stuff and is very knowledgeable.
Pepe's Plants
https://www.pepesplants.com
In South Florida (I'm not sure where). Can order online. He has a YouTube channel too.