Today I want to show you how to grow blackberries. I’ll take you through the steps needed to grow blackberries from seed, and cuttings, how to care for them, and when and how to harvest. Although the focus is on growing, pruning and harvesting I’d also like to share the amazing health benefits blackberries have.
These little berries are powerhouses filled with antioxidants and beneficial phytonutrients that will blow your mind!
Whether you are a complete novice or a seasoned gardener, you’ll find these step-by-step instructions helpful and easy to follow. I will share growing tips with you that I have picked up over the years as well as solutions to problems common to blackberries.
For gardeners that want quick results, I recommend choosing a variety that is suited to your region and that is ready to be planted as soon as spring begins. Your local nurseryman will guide you on what type of blackberry to get. There are many exciting new varieties of blackberry plants available and we have provided an easy-to-use chart that will help you decide which blackberry cultivars to plant in your garden this spring. Trailing, erect, arching, thornless, or prickly, there is a blackberry bush with your name on it!
Want to grow blackberries indoors? Or in tubs? We have you covered. This simple guide on how to grow blackberries will inspire you to grow blackberries as well as many other types of berries and fruit. The more food you can grow yourself the better.
Let’s get started!
- 1 The Blackberry Backstory
- 2 Blackberries: Benefits and Uses
- 3 How to Grow Blackberries
- 4 How to Plant Blackberries
- 5 How to Care for Blackberries
- 6 Harvesting Blackberries
- 7 Blackberry cultivars: choosing the best type of Blackberries for your garden
- 8 Blackberries: Common Pests and Diseases
- 9 Conclusion
- 10 Frequently Asked Questions
The Blackberry Backstory
Before we get onto the “how to grow blackberries” section let’s learn about where they come from, what they are, and why we love them. These deep purple berries are not even berries in the botanical sense. The term “aggregate fruit” is the correct term because they are made up of multiple druplets.
Their rampant growth habit has caused them to be “outlawed” in many places. They are considered naturalized in many countries but are classified as invasive weeds. In the US, thornless blackberries have been developed. The advantages of thornless cultivars will be listed further on.
Due to the extraordinary health benefits of the Blackberry, attention has been given to developing hybrids and cultivars and today we have varieties with the following attributes:
- Higher yields
- Larger fruit
- Tastier fruit
- Fruit suited to fresh market
- Fruit suited for processing
- Less susceptible to pests and diseases
- Can tolerate cooler and warmer temperatures than wild species
- Primocane-fruiting cultivars
- Traditional floricane-fruiting species
Where do blackberries come from?
Blackberries are native to Europe but there are over 375 species! So it’s no surprise that various types of blackberries are found across Europe, Asia, Africa, and both the North and South Americas. Blackberries grow across the world and you will find different species in almost every country imaginable.
Many other berries like raspberries, loganberries and boysenberries are closely related to blackberries. It is from this ability to cross-breed that we are able to have so many new varieties that are easy and rewarding for the home gardener to grow.
But the berries we get are not the result of random cross-pollination. Research and development have been going on for decades. The results of which are evident in cultivars like:
- Navajo (the first thornless cultivar, floricane-fruiting),
- Everthornless (cloned),
- Prime Ark Freedom (thornless, primocane-fruiting),
- Prime Ark (vigorous thorny, primocane-fruiting),
- Triple Crown (trailing), Black Diamond (trailing, thornless), and many more popular cultivars that get adapted to a range of preferences, and climates.
There are now also varieties of blackberries that produce two crops in one year. These blackberries bear fruit on both the primocanes (1st-year canes) and the floricanes (2nd-year canes).
How do blackberries grow?
Blackberries are called brambles because their growth is so vigorous, and their stems so thorny. Left unmanaged they form impenetrable hedges. This can be useful for creating “fences” or barriers around growing areas of other fruits and vegetables that may be susceptible to being grazed by wildlife or domestic animals.
Blackberries, especially trailing blackberries, have canes that reach lengths of 20 feet (over 3 m). These plants will need blackberry trellises. A blackberry trellis is not complicated to rig up.
Anyone growing blackberries with such vigorous growth must be prepared to prune, train, and trellis blackberries. This type of attention will produce strong plants that fruit well. Healthy blackberry plants are less prone to fungal and bacterial infections.
There are trailing blackberries, arching blackberries, and erect blackberry bushes. All 3 types can be cultivated by gardeners and choosing the type will depend on what you want them for (eating fresh or preserving).
There are also thornless cultivars. These are a dream to cultivate in a home garden and as you’ll see below, these new cultivars get hybridized to produce many variations suited to both domestic and commercial growing.
The erect blackberry bush is ideal for container growing. The rambling type, as mentioned, can be used as hedging. But the thornless blackberry cultivars may be best suited for the home gardener. Blackberry prickles are aggressive and sharp and make pruning and harvesting a bit of a nightmare, to be honest. I cannot stand wearing gloves when I garden so I always try to avoid thorny plants where I can.
Further down is a list of the most available and popular thornless blackberry cultivars. The advantage of the thorny types is that they produce tastier fruit and have much more vigorous growth, so of course, the yield will be higher.
Blackberries: Benefits and Uses
Blackberries have been eaten by humans for over 2,500 years. They have many culinary and medicinal uses. The entire plant is used in remedies for various ailments. The leaves and shoots can be chewed for mouth ailments like bleeding gums.
Blackberry tea (infusion) treats bacterial infections, like whooping cough. The roots, with their astringent properties, get used in treating dysentery and diarrhea. And concoctions made from leaves, stems, and bark get used to treat stomach ulcers.
Today there are easier ways to treat these conditions so many of the blackberry’s healing properties belong to the history books and get filed under “Folk Remedies”. But when it comes to eating these juicy berries the benefits have not been lost.
So before we discover how to grow blackberries from seeds and cuttings, let’s see how nutritious they are and what they can do for us healthwise.
Health Benefits of Blackberries
1. Blackberries are high in vitamins and minerals
Blackberries are nutrient-dense, high in fiber, and loaded with anthocyanins and ellagic acid. Studies show these phytochemicals have potential to reverse damage caused by free radicals, thus offering benefits that are anti-aging, anti-cancer, and anti-oxidant.
Blackberries are considered a superfood because they are low carb, nutrient-dense, high-fiber, and contain protein. They are loaded with antioxidants called anthocyanins. Antioxidants neutralize free radicals within cells, these oxidized cells increase the risk of inflammation which leads to diseases like cancer.
2. Blackberries are low carb and low fat
Blackberries have a low glycemic load (4). Eating meals that have low glycemic loads keep blood glucose levels stable. This prevents energy spikes and crashes (due to elevated blood glucose). Unstable blood glucose levels may lead to insulin resistance, metabolic diseases, inflammatory conditions, pre-diabetes, and eventually Type 2 Diabetes (T2D).
3. Blackberries help fight infection
The combination of high levels of manganese, vitamins C and K, along with the amino acids, fiber and antioxidants give blackberries antibacterial and antioxidant properties. By adding blackberries to your daily diet you may get the following benefits:
- Strengthened immunity ( antioxidants)
- Strengthened skeletal system ( Bones support immune system)
- Improved blood glucose levels and blood lipoprotein profiles. (Decreased risk of heart disease, T2D, and weight gain)
- Efficient nutrient absorption during digestion
When the immune system, digestive system and circulatory system function optimally then many ailments and pre-cursors to more serious diseases may be prevented. Blackberries (and other purple food) are part of the “rainbow” diet that we should all be eating for optimal health.
Uses of Blackberries
Blackberries are best eaten fresh. They are great on their own or served with cream or ice-cream. Some types are suited for the fresh market and others are picked for processing.
Blackberries get used for:
- Frozen products
How to Grow Blackberries
Blackberries can be grown from seed, leafy stem cuttings, tip layering, and root cuttings. And the home gardener can grow blackberries using any one of these methods. But it may be worth buying a young plant that has already had a year to grow. These are readily available at nurseries, garden centers, and even online.
If you are growing from seed you will have time to prepare the site where you’ll plant them out in early spring. If you buy a root stock then you can plant it 4 weeks before spring which gives the plant time to settle before the growth phase kicks in.
Blackberries need adequate sun to produce a good yield of quality fruit. Some varieties are susceptible to very cold weather and this can damage buds, which will affect the yield and quality. For the home gardener, or the small farmer, growing blackberries is easy, but it does take a fair amount of work.
There are three main growth habits and each one has its own set of requirements and advantages over other cultivars. We will discuss all three types and give simple instructions on how to care for each type.
How long does it take to grow blackberries?
In the first year, the blackberry plant will concentrate on its vegetative growth cycle. During this stage, it produces canes called primocanes. These canes do not produce fruit in the traditional floricane-fruiting varieties. In the second year the floricanes develop and fruiting begins between May and July.
When you transplant a blackberry from a nursery bag or another pot make sure it has been cut back. See the section on pruning blackberries. Also, if it is a trailing blackberry you can buy a ready-made blackberry trellis that can be inserted into the pot after transplanting.
The image above shows you what a typical blackberry plant looks like before planting. Obviously, when planting out seedlings the method will be similiar but the fruiting cycle will take longer.
When you plant a blackberry plant, like the one shown above, you can expect it to take about 3 weeks to start shooting out new green growth. It will take another 60 -90 days before you see budding and then a further 25-40 days before you can harvest. The time will also depend on the cultivar you have selected.
How to Grow Blackberries from Seed
Here is a step by step guide for growing blackberries from seed:
- Start by buying fresh berries (or seed in a packet). If you buy fresh you will need to extract the seed.
- How to extract seed: Place the fresh seed in a processor and blend to a pulp.
- Transfer into a sieve, with holes large enough to let pulp seep through.
- Using a spatula gently press remaining pulp through sieve.
- Wash seeds (still in sieve) until the flesh is removed.
- Spread seeds onto a coffee filter and allow to dry.
- Place seeds onto damp peat moss.
- Place peat and seeds in a sandwich bag and refrigerate for 3-5 months. The seeds will begin to crack open in the cold.
- In spring remove bag and plant seeds.
- How to plant seed: The container (preferably a nursery flat) must have drainage holes. Add soil to until full to the top. Water and when soil has settled and is damp right through, place seeds on top of soil.
- Cover with not more than 1/16 inches of a seedling mix ( must be fine with no bark bits).
- Keep moist. Place in a warm, protected area that gets partial sun. To transplant from the seedling tray into a pot you will need to get a tub and see our instructions on how to transplant into a container.
- When the blackberry plant gets bigger you can either add a trellis to the pot so you can train the canes and support them. Or you can transplant into the ground on a site that has been prepared. See section titled “How much space do blackberries need?”
Where Do Blackberries Grow?
In the US, blackberries grow in the Southeastern US, especially in Oregon. They are grown commercially in British Columbia, Eastern Canada, Midwest, and California.
Blackberries enjoy temperate regions that experience mild winters and cool summers. When the climate is too humid, too cold, or a high rainfall area, blackberries are susceptible to a host of fungal infections.
When they grow in areas that get less than 6 hours of direct sunlight, the crop will perform poorly and produce a lower yield of fruit that does not ripen properly. They also need soil that is rich in humus and drains well. If blackberries don’t get enough nitrogen, potassium, and phosphorous their leaves will turn yellow, the canes will be weak, and the fruiting poor.
How to choose the perfect site for growing blackberries
When choosing a site for blackberries, choose an area that:
- Gets 6 hours or more of direct sunlight every day.
- Is not low-laying. This means when it rains or gets water the water must not collect in a pool around the base of the blackberry plant. This is because blackberries are susceptible to root rot.
- The site should have enough space for the number of plants getting planted. (See “How much space do blackberries need.”)
- If the area is protected from wind, this is even better.
- Make sure no plants from the Solanaceae family have grown there over the last 5 years. These plants host a fungus that will attack blackberries.
How to Grow Blackberries from Cuttings
Root Cuttings: Blackberry root cuttings should be 3-6 inches (7-15 cm) in length. Place them in cold storage for 3 weeks at a temperature of around 40 F (4 C). When ready to plant, plant them into a mixture of half peat and half sand. This will provide good drainage.
Root cuttings are used more often than other types of cuttings. When taking root cuttings, make a straight cut close to the crown and an angled cut further down. Bundle these roots and tie them up, before refrigeration.
Stem Cuttings: Take cuttings from the primocanes because floricanes die after they bear fruit. Cut them 4-6 inches (10-15 cm). Place them into the same peat/sand mix as for root cuttings. When planting the cuttings before they have rooted, plant them 5-7 inches apart.
Keep in a shady, well-ventilated area. They should root in 3-4 weeks.
How to Grow Blackberries Indoors
- Choose Blackberry plants with an erect growth habit for indoor planting.
- The pot should be 12-14 inches (30-35 cm).
- Place pebbles in the bottom.
- Fill with soil that is a mixture of organic compost and a slightly acidic potting mix. Leave a space of 1-2 inches from the top of the pot.
- Transplant as you would for a container.
- Before planting, water the soil and allow it to soak through so that the entire mix is moist.
- Make sure it gets 6 hours of daylight. So place the pot in a suitable place. Or use a growing lamp. The advantage of planting blackberries indoors is that you can protect them from cold, which may damage new growth and young fruiting buds.
If you’re growing Blackberries indoors, Prime-Jim and Prime-Jan are good varieties to choose. Both these types are primocane-fruiting varieties.
How to Plant Blackberries
How much space do blackberries need?
Due to the trailing, rambling nature of blackberries they must be planted with enough space between plants to allow for ample growth of the canes. Plant each plant 6-7 feet (2 m) apart. And in rows that are at least 3 feet (1 m) apart.
What soil do blackberries like?
Blackberries like a soil with good drainage. The soil must be rich in organic matter, or humus. The soil must be slightly acidic, anywhere between 5.5 and 7.0 is perfectly fine. Soil that is too sandy or has too much clay will not do.
Blackberries suffer from fungal diseases so it is crucial that the soil drains well and contains enough nutrients to keep the plant healthy.
It is advisable to cover the base of your blackberry plant with a thick layer of mulch, this keeps in the moisture and cuts down on the amount of water you need. It also keeps the perennial roots of the blackberry warm.
What is the best climate for Blackberries? Warm vs cold
When you’re growing Blackberries, they prefer temperate regions that experience mild winters and cool summers. That said, varieties and cultivars are now available that have been adapted to handle slightly more extreme conditions. But in general, the traditional floricane-fruiting types will do best in a temperate region. In the States, this equates to Zones 5-10. Click here to go to a chart of Zones in US.
If you live in Zone 4 you’re in luck because there are a few cultivars adapted to colder regions. “Doyle” is a thornless blackberry suited to the southern regions in zone 4 while “Illini Hardy” is a thorny blackberry that is cold hardy.
Many blackberry plants are cold hardy to -20 to -25 F. And most erect varieties are more cold hardy than trailing types.
For regions with dry windy summers: Plants will need 200-300 hours of sunlight per season. Trailing varieties will do okay in zones 7,8, and 9.
How to Set up a Blackberry Trellis
Why do you need a trellis if you’re growing blackberries?
Well, besides the fact that they need to be supported due to their rambling, trailing growth, there are other advantages. By training your canes onto trellis wires you give the plants more exposure to light. This will increase both foliage growth and your yield. By separating the berries from the front and back, they get more light and space.
There are various ways to build a blackberry trellis and the way you set up your trellis will depend on your skill set and budget. There are loads of YouTube clips available. These clips will guide you through your blackberry trellis set up with ease.
The clip below is a very easy-to-follow guide on how to train your mature plants and cut them back. The clip following that shows you how to build your trellis before planting, and also discusses choosing a site.
The reason for trellising blackberries is threefold:
- Support the canes
- Increase the space between canes and thus also increase light to all parts of the plant
- Train the plants and make it easier to maintain when the time comes to cut back and prune.
When deciding where to plant your blackberries, choose a site that has not had tomatoes, green peppers, potatoes, or brinjals growing there over the last 5 years. These plants host a fungus called Verticillium, which blackberries are susceptible to, so growing blackberries in the same soil is not advisable.
How to transplant a Blackberry bush into a bigger tub
This short step by step guide explains how you can get fruit from your blackberry in 130-150 days.
Transplant blackberries in late fall. Before you transplant your blackberry plant you must prepare the container. Get a container from your local nursery or recycle an old pot or tub that you have lying around. The pot must have proper drainage. Make holes underneath if need be. Then fill the bottom with pebbles.
Make your mix by adding some lime, organic pellets, and organic compost to a potting mix. You can buy ready-made mixes if you are still a novice but seasoned gardeners usually have their own soil mix recipes. As long as the soil is slightly acid and drains well, you will be fine.
Fill a third of the pot, saturate the soil, and repeat until all the soil is added. Take out some of the soil and into the hole add some rich compost mixed with a small pot of bonemeal. Your blackberry is now ready to be planted.
Once it is in the hole, cover with the remaining soil (also moist but not wet). Secure the plant by pressing lightly around the base. Add your trellis if it is a trailing variety.
How to Care for Blackberries
There are two types of pruning for blackberries and each kind of blackberry pruning serves a different purpose.
Tip Pruning Blackberries: This involves cutting the blackberry tips just above the node of the second or third leaf. This invigorates growth and will result in more foliage which means more fruit. This type of pruning must be done in early spring.
Cutting Back Blackberries: Pruning blackberries after they have fruited ensures that the next season’s growth will be lush and strong.
Cutting back deadwood (the floricanes bear fruit once and then die) is crucial to reduce the risk of certain diseases. Once the blackberries are done fruiting (late summer) then you need to cut off the floricanes, leaving only the primocanes.
You can see which canes need cutting by their color. Leave the canes that are green or reddish and cut back those that appear greyish and dry. Cut them as close to the crown as you can.
Growing blackberries requires enough nitrogen in the soil, especially during the first year’s growth. The following year the soil needs to be fortified with plant food high in potassium and phosphates to encourage fruiting.
Organic fertilizers are always preferable to synthetic fertilizers. This is because the soil is a living organism and applying synthetic fertilizers destroy the microorganisms that keep soil healthy and reduce the occurrence of fungal and bacterial infections.
How much water do blackberries need?
Weeks 1-3: Water often and keep the first 1″-2″ of soil moist. Water in the daytime.
3 weeks up to harvest: Water less frequently, maybe once a week. Still maintaing 1″-2″ of water.
From harvest: Increase the water to 4″ during harvest time. This means the watering will be deeper and supply the entire root system. Berries that get enough water will be that bit more plump and juicy.
When is the best time to harvest blackberries?
The best time to pick blackberries is in the morning, on cool dry days. This will extend the shelf-life. Blackberries are soft so they must be handled with care to avoid crushing. Pick the blackberries and place them on trays or in shallow tubs. The shelf-life of blackberries is 4-5 days. keep them in the fridge to extend the shelf-life.
You will know when they are ready to be harvested because they will be very shiny. As soon as the shine fades they are ready to get picked. Blackberries that don’t get enough sun will not be sweet.
In Oregon fruit ripens from mid-June to August. The fruiting season lasts 4 weeks for each cultivar. Commercial farmers will grow different varieties to get as long a harvesting season as possible. It is also possible for gardeners to plant some of these varieties to get fruit at different times.
Blackberry cultivars: choosing the best type of Blackberries for your garden
Growing thornless Blackberries
- More vulnerable to pests like birds and grazing wildlife.
- More sensitive to colder weather
- Canes are softer, can only be hand-harvested.
Growing trailing Blackberries
- Best suited to outdoor planting.
- Must have well-drained soil.
- Least cold-hardy of all types.
- Best for machine-harvesting
- Produces the highest yields
- Generally, produce better tasting fruit
Growing erect Blackberry cultivars
- Suited to containers and small gardens
- Developed for the fresh market
- Can only be harvested by hand, not machine.
- Primocane-fruiting varieties are erect.
The chart below gives a list of cultivars and their info. I hope this makes choosing your next blackberry cultivar easier. All the varieties chosen are suited to home gardens and small farms. Most these blackberries are suited to the fresh market only. The trailing species will usually also be good to use in preserves and jams or any other type of processing.
|Obsidian||Trailing||Vigorous thorny||Large, firm||good||High early ripening|
|Silvan||Trailing||Vigorous thorny||Large soft||good||High|
|Cascade(Cali climates)||Trailing||Vigorous thorny||Small med||good||Medium early ripening|
|Black Diamond||Trailing||Vigorous thornless||Large firm uniform||good||High|
|Columbia Star||Trailing||Vigorous thornless||Large firm uniform||good||High|
|Marion||Trailing||Vigorous thorny||Med soft uneven||good||Med|
|Wild treasure||Trailing thin canes||Vigorous thornless||Small uniform||good||Low to high (cane damage)|
|Triple Crown||Semi-erect||Vigorous thornless||Med large||good||Med high|
|Ouachita||Erect||Vigorous thornless||Med firm||fair||Med|
|Illini hardy||Erect||Vigorous thorny||Med large||bitter||Med|
|Prime-Ark||Erect||thornless||Large||good||Med (early sep)|
|Prime-Jan/Jim||Erect||thornless||Large soft||fair||Med (late aug)|
|Prime-Ark-freedom||Erect||thornless||Small med||fair||Low-high (early sep)|
Blackberries: Common Pests and Diseases
Pruning blackberries is good hygiene practice. Removing the dead canes reduces infestations of Cane Borer Beetle.
Fungal infections can wipe out entire crops. The best way to minimize fungus on blackberries is to make sure they are not grown in damp, humid conditions. Good ventilation, adequate sunlight and space helps.
Copper fungicides can be used to treat some types of fungus but often the best route to follow is to remove all the infected parts and burn them. Sometimes it may be necessary to remove nearby plants to, especially if they are growing wild, close by.
These are the fungal infections most commonly encountered when growing blackberries:
- Algal spot – treat with copper fungicide
- Anthracnose (Dieback) – more prevalent in trailing varieties
- Cane and Leaf Rust – not systemic so it won’t affect blooming. Prune out infected parts and burn.
- Fruit Rot – Ensure timely harvesting and spaced planting will reduce this fungus
- Orange Rust – affects fruiting, fungicides don’t work. Many thorny varieties are resistant to Orange Rust.
- Double Blossom – affects fruiting. Remove wild berries nearby. Remove infected parts and burn. Cut all canes right back after fruiting. New thornless varieties are less susceptible.
- Leaf Spot – similar to Anthracnose, usually removing infected parts is enough, and applying chemicals is not necessary.
Grow low-spreading herbs like mint, lemon balm, hyssop, chives, borage, and thyme. These are all excellent companion plants and get grown as groundcovers, or in between blackberries. Companion planting reduces disease and boosts the health of the plants.
Despite what many people say, blackberries are easy to grow. They may be susceptible to fungal diseases more so than other crops but if you employ good gardening practices and maintain good plant hygiene, this should not be a problem.
With so many blackberry cultivars and varieties available, growing blackberries is easy in the climate they are suited to. But you can also grow blackberries indoors and in pots.
Blackberries are loaded with antioxidants and nutrients that have cancer fighting properties. Growing Blackberries and ddding a cup of berries to your daily diet will give you fiber, vitamins and protein. Blackberries also have antibacterial properties. Eating blackberries regularly may reduce the risk of diseases like diabetes, heart disease and obesity.
Frequently Asked Questions
What are the health benefits of Blackberries?
Blackberries are a low carb, low fat, nutrient-dense superfood that is high-fiber and contains protein. They contain antioxidants and high levels of manganese, vitamins C and K, and amino acids. Blackberries are antibacterial and antioxidant, improve immunity and blood sugar levels. Check out this article for more info about Blackberries and their many benefits.
Can you grow Blackberries in pots?
Yes. Most varieties of Blackberry do very well in pots and planting them in containers prevents them from spreading prolifically and taking over your yard. Check out this guide for all the info you need to know about how to grow Blackberries.
How to propagate Blackberries?
Blackberries can be propagated from seed, stem cutting and stem layering as well as by splitting a mature plant at the root. Check out this guide for all the info you need to propagate Blackberries successfully.
How long does it take to grow Blackberries?
In the first year, the Blackberry plant will concentrate on its vegetative growth. During this stage, it produces canes called primocanes. These canes do not produce fruit in the traditional floricane-fruiting varieties. In the second year the floricanes develop and fruiting begins in the spring and summer.
https://en.wikipedia.org/wiki/Blackberry https://plantvillage.psu.edu/topics/blackberry/infos/diseases_and_pests_description_uses_propagation https://www.thegardener.co.za/grow-to-eat/fruit/brambles/ https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1617.pdf https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning http://www.homegardeners.com/blackberries_propagation-seeds.htm https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635667/ htps://www.arborday.org/trees/fruit/care-blackberry.cfm https://plantdiseasehandbook.tamu.edu/food-crops/fruit-crops/blackberry-dewberry-and-boysenberry/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4192974/ https://planthardiness.ars.usda.gov/PHZMWe