Hosta are among the most popular of shade plants, and no wonder. With so many varieties, in so many different sizes and leaf colors, you could have a wonderful shade garden using nothing else.
They are usually listed as hardy from zone 3 to zone 9, and even for zone 2. You can see from that, and northern gardeners will agree, that they enjoy colder zones, with crisp, cold winters and plenty of rain through most of the year. But of course, gardeners being gardeners, we get lots of enquiries about growing Hosta plants in warmer areas. If you do the Google thing and search the internet you will find lots of conflicting advice and information that is inaccurate (I am too polite to say, “wrong”!). So here is some more accurate info on this tricky question, and advice on which varieties to grow if you do live in hot areas.
Hosta Plants Need to Sleep
Anyone who has grown Hosta is automatically answering this with, “shade and moisture”, and you aren’t wrong. But to understand why Hosta – and most other plants too – grow well in some places and not well in others we need to lift the lid and look inside the growth of plants.
When you think about it, it’s amazing that plants know it is spring, and start growing, and know it is fall and go to sleep. It isn’t just temperature – try cutting a few tree branches in October, putting them in a vase of water and bringing them into the warmth of your house. Nothing will happen. Do it again in February, and most trees will then send sending out leaves or flowers. People like to do this with forsythia bushes for example, to get an early start on spring. But what has happened to those branches that brings about this change?
Hosta Plants Learn When to Wake Up
Imagine you are a tree that lives in the tropics. There is lots of competition, but you see places north of you where there are fewer plants, because it is cold for part of the year. So you spread to that place. You figure out that if you drop your leaves in fall, and go to sleep, you will survive the cold.
Trouble is, how do you know when to wake up? If you rely on it getting warmer, what easily happens – and if you live in cold regions you will know this – is that in late winter you can easily get some warmer days, but they are often followed by the return of cold. If you, the tree, wake up the first time you feel warmth, changes are your nice new leaves are going to be killed by the return of winter – oh, oh! Plants have mechanisms to protect dormant buds from winter injury, and they can stand low-temperatures, but this disappears the minute the bud starts to develop, even before it begins to grow. This is why certain plants – like some varieties of the forsythia we already mentioned – will grow happily in zone 4, but hardly ever flower, because the buds wake up too soon, and are killed by the cold before we even notice them.
So over millions of years plants have evolved a mechanism for measuring how long it has been cold. You might have heard of this with fruit trees, which need a certain number of ‘chilling hours’ to open their flowers properly in the spring. If you are interested in this topic for fruit trees, here is a blog on it. What is less well known is that chilling hours applies also to most perennial plants as well, which also don’t want to be bursting into leaf on the first freak winter’s day.
Hosta and Chilling Hours
The temperature at which chilling has an effect on buds is usually taken to be 40 or 45 degrees Fahrenheit (roughly equal to 4 to 7 degrees Celsius). Some sources pick the middle and say 43o. For most Hosta species it takes a minimum of 30 days below that temperature – not continuously but cumulatively – for the plant do develop vigorously in the spring. That translates into around 700 chilling hours. If this doesn’t happen, yes, leaves will grow when the weather warms up, but growth will be weak, and become weaker each year, so that in a few years the plants will probably die.
Take a look at this chilling hours map (you might find it useful for fruit and other plants too), and you will see the problem for Hosta. A whole strip of the south, everything in yellow and shades of orange, doesn’t have that many hours. Look at the northwest, though. Those are regions that are listed as zones 8 and 9, but their climate is very different. They have mild winters, but they are cold enough to give any plant lots of chilling – no wonder Oregon is a big center for growing plants. Compare that to northern Florida – also zone 9 – what a difference! So what we are saying here does not apply to zone 9 in the northwest, where Hosta thrive.
Hosta for Warm Zones
So, even if you have irrigation and lots of nice shade, forget the idea of planting a bunch of Hosta in your Florida garden and expecting them to grow well. You will get very mixed results – mostly failures. The chilling need isn’t absolute – without it Hosta plants will grow new leaves in spring, and probably stay semi-evergreen too. But the growth will be weak, open and there won’t be many leaves. Each spring will be worse, so that within just a few years they will stop growing entirely, and die.
But not all of them. Hosta come mostly from China and Japan, which both have hot and subtropical areas. There are quite a few species that are adapted to hot areas, and need very little chilling. The only one that is widely grown and available to gardeners is the plant called Hosta plantaginea.
This species needs just a few chilling hours, probably less than 200, so you can see it will succeed in most of Florida, and there are reports of it growing fine even in the far south of that state. Research led by James Kessler, of Auburn University, Alabama, showed that while even short periods of chilling do increase the number of leaves, it isn’t essential for new growth. (Effect of Chilling Duration on Growth of Hosta plantaginea and 11 Related Cultivars, Journal of Environmental Horticulture (2004) 22 (1): 37–40).
So, if you want to succeed with Hosta in zones with mild winters, look for varieties of this species – it is your best bet. The most well-known and widely-available is one called ‘Royal Standard’. Some authorities think this is a hybrid, but even so, it is mostly Hosta plantaginea. With large, round, dark-green leaves it’s a handsome plant with a bonus. In cold areas it flowers only reluctantly, but in warm zones it is a vigorous bloomer, and this is the only species with fragrant flowers – that’s right, the large, white, trumpet-shaped flowers release a beautiful lily-like fragrance – plant it beneath a window on the north-side of your house to let it delight you on a summer breeze. Flowering over a long period from late June into August, it’s a winner.
Here are some other varieties of Hosta plantaginea, or hybrids where it is a parent, to enjoy – who said you can’t have a Hosta garden in the hotter parts of the country?
‘Aphrodite’ – a unique plant with large flowers that are double – many petals tucked inside the white trumpet of the bloom.
‘Guacamole’ – a lovely variety with chartreuse leaves making a mound up to 4 feet across.
‘Honey Bells’ – a large plant, but with narrower, wavy leaves that the original
‘Stained Glass’ – the golden yellow leaves of this plant have a broad green margin. Again, with white, fragrant flowers
‘Summer Fragrance’ – a bold clump, and the leaves have a thin white margin. The pale lavender tone of the fragrant flowers gives away its hybrid origin.
There are a good number of other varieties that have been created in recent years that are not yet in the general garden market – so more treats to come for Hosta-lovers in hot zones!