Updated: Dec 2
Dahlias are easily my favourite flower of all time but they do tend swing back and forth on the fashion pendulum. Back in the 1800's they were known as Georginas and were frightfully expensive. They were a real status symbol costing one hundred pounds a tuber. Wealthy families would plant large borders full of them and invite guests around for afternoon tea to show them off. By the 1950's they had come down in price and in the drab era of brown and beige lost their attraction. They were considered showy and vulgar and many of them were lost.
Every year gardeners up and down the country report that their Dahlias are slow through the summer or that they have short stems. I assure you this is normal! Dahlias are at their best in the early autumn - in the UK this is September time. They originate from equatorial regions such as Mexico, Columbia and Central America, where the days and nights are equal lengths. So the autumn equinox which falls on the 23rd September is the time they love the most. Not too hot, not too cold and equal day and night.
In my last Dahlia blog "Growing Dahlias" I gave a general overview of all aspects of Dahlia growing and propagation . This time I will focus on what you need to do in Autumn to store your Dahlias for the winter and ensure that you can re use as many of them as possible next season.
In areas which do not suffer too much from a hard frost lifting is not necessary but for those in colder regions it may be wise to lift and store them to secure your tubers for the following year, or if you have wet clay soil/poor drainage which will rot the tubers through winter.
In some southern parts you can experiment with leaving a few in the ground to see if they do make it through the winter just ensure they have a good covering of mulch and free raining soil. We do find that on our field that they do much better lifted as otherwise they would rot.
Dahlias need to be lifted out of the ground just after the first frosts or in the case of very late frosts when they stop being viable and producing blooms. You can even wait for the second frost before lifting as this will give the tubers more time to mature which will help them through the winter time - This is usually by mid October where I live in the South of England. You will know instantly when you have had a frost as the leaves will all be turned black. You will then need to cut down all of the stems & leaves, leaving just 10cm or so of a main stem to help lifting.
Using a garden fork loosen the soil around each dahlia and lift the whole tuber out of the ground. Try to do this on a dry ish day so that the excess soil can be easily brushed off. Take as much soil off as possible without damaging the tubers, so bashing them on the ground is a no no!!
If you only have a few tubers and are growing in the garden at home you won't mind too much about correct labelling but if you want to grow and propagate them by colour then correct labelling is a must. It's actually like an obsession and I don't think I have had a single year yet without at least a handful labelled as "unknown variety". It's frustrating and this year is my worst ever with over half of mine labelled like this - my own stupidity as I transported them to the field all the pots were knocked over and got mixed up. I've also had the birds pull by labels out of the ground and I've heard of mice gnawing through the string when tied to tubers! So I have found that double labelling is the most successful.
Firstly I label each tuber with a marker pen when they are in storage over winter ( Jan or Feb time) I don't do this straight after lifting because they are too wet and the marker pen gets clogged up. I then label each pot when pre sprouting with a label which follows the tuber into the field and then when the flowers can clearly been seen I double check all the labels in the soil and add another label tied around the main stem of the plant. Then I'm absolutely exhausted !!!
Drying/short term Storage
Once all of your Dahlias are lifted store them in a cool dark place which is frost free until you are ready to wash and split them.
You are essentially removing them from the ground to ensure that the frost does not damage them and putting them somewhere safe out the way to dry out a little bit. I store mine in plastic crates in my garage for a few weeks until I have the time to deal with them.
Once you are ready to store your tubers for the winter you will need to give them a good wash with a hoze pipe jet. It's a dirty job and the power from your regular kitchen tap will not be strong enough to clean the tubers well. You can see from the picture how clean the tubers should get. This is essential to ensure any creatures and soil are washed off so they wont be eaten in storage.
They can immediately be split for winter storage or stored as whole tubers !
Dahlia Anatomy & Splitting
Each plant consists of a stumpy stem or stems and will have several swollen parts attached. They are really not the prettiest things to look at ! These are called tubers and to grow into a successful plant each Dahlia needs a tuber with at least one eye. The section where all of the tubers and stems meet is called the crown. Dahlia stems will grow from buds/eyes on this crown. Look very closely all around the crown of the tubers for the eyes and you will be able to see small freckle like spots. Some tubers will have lots and others just a few. At this time of year that are not easy to spot and you need to look very very closely! They are easiest to spot straight after lifting and again in the spring just as they begin sprouting.
Remember the tubers are not roots – they are a food store for the plant and if a tuber does not have an eye then it will not grow no matter how much care and attention you give it.
It can be difficult to know where to start but if you begin by splitting a tuber in half across the old main stem you are half way there already. Try splitting between the tubers so that you get less wastage, but inevitably you will end up with a few which have been sliced through. Make sure that you throw these - they will just rot in storage and put the rest of your stock at risk. You can then split both of these halves again so you end up with four quarters if your tuber is really big.
Now it’s easier to look at each tuber and decide if it’s viable or not. Carefully check the crown of each tuber looking for at least one eye. Some will have none – these can be discarded but others may have many. Then simply cut this tuber away from the rest taking care to cut it away with the eye and some crown. Repeat this for each tuber in turn. If you are unsure if you can see eyes or not then there is no harm in keeping them all and checking them in spring when the eyes are much easier to see.
If you have any tubers which are a bit wobbly and broken remove these ( Middle picture below) and do not store them - they may rot. At the same time you can also trim off all of the fine roots as these will not be needed for winter and new ones will be produced next season.
Once you have discarded all the parts without an eye and done your trimming you will be left with a bunch of nice neat looking tubers just like the picture on the left. From that one clump which you planted in springtime you can get as many as 10+ viable tubers which will in turn make a huge clump of tubers for you to divide next year!
There are a few different ways to store tubers but the below method is the one I have used for years and it works well for me with minimal loss.
You will need a container to store them in such as a lined bulb crate or a plastic box/bin, and a medium to cover them. There are so many mediums to store tubers but the most important thing is to keep them hydrated and frost free. You can use vermiculite, peat moss, spent compost, wood shavings etc. I now use wood shavings - the kind you can buy from the pet shop for rabbits. Simply take your container and put a layer of your medium in the bottom - just a couple of cm's is enough. Place each tuber onto the medium and ensure that they are not touching then cover the tubers with another layer of your medium. The label which you used for short term storage can then be placed inside the container.
Once you have done this store them away in a frost free place at 5-10 ℃. It’s a good idea to check on them once a month until spring time. If the tubers are looking shrivelled then a light misting with some water will help to keep them going and using a plastic box with a lid also helps. They should not be left to dry out too much or be left wet or they will rot.
I check mine after 2 weeks first- yes every single one unpacked from storage checked and then packed back again - this is to remove any rotting ones as otherwise the rotting may spread throughout the crate all winter long. I then check them monthly/bi monthly after this and remove any rotting tubers. After the first check it is rare to find many rooting ones but its best to be safe. If you suffer from rodent attacks it is also wise to ensure you use something with a lid !
I have experimented using shrink wrapping film instead of storing in a medium but it rotted all of the tubers by sealing in the dampness. They really do need to be bone dry when storing like this and I haven't managed to get it right as yet so I will continue with the wood shavings for now and experiment with the cling film.
During one of my checks - usually in Jan/Feb is when I then label each one with a marker pen! This is when they are dry enough, before that the the market pen just wont stick.
Small numbers of tubers
If you only have a handful of tubers then its not necessarily worth the effort splitting them at the end of the season. This way you can wait for springtime to divide them when the eyes have started to form.
If you would like to read more about Dahlias then check out our blog post Breeding Dahlias