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When to cut back dahlias


Fall Dahlia Care — Seattle's Favorite Garden Store Since 1924

Denise Read

Planting & Plant Care

Denise Read

Planting & Plant Care

Dahlias reign supreme in the late summer garden. They are vigorous growers and reliable bloomers; they add luster to the landscape with their foliage in various shades of green and blooms that range from petite pom-poms to flowers the size of dinner plates, in an entire rainbow of colors; they are marvelous in a vase. 

Dahlias die back each year as autumn advances, but, with the proper care, the tuberous root system can live on to produce a stunning display year after year. The advice in this post is based on many years of growing dahlias in a low-lying area of Seattle with relatively moderate winter temperatures and excellent drainage. It may differ from other advice available. 

If dahlia tubers freeze or get too soggy, they can rot. If this is a possibility in your garden due to a colder than average microclimate or poor drainage, tubers can be lifted and stored indoors for the winter. Otherwise, with normal winter temperatures and good drainage, tubers should survive in the ground reliably year after year in the PNW Seattle area. 

Keeping Dahlia Tubers in the Ground Over the Winter

After a hard frost, when the dahlia foliage and stalks die back, cut the plant back to about 6 inches from the ground. Some growers prefer not to cut them back because the stems are hollow and cut stems can fill with water and potentially cause the tubers to rot. To prevent this from happening, cover the tubers well with a mound of mulch that will shed water such as a straw, leaves, or compost. In the spring, you can remove thick leaf or straw mulch; your dahlias will sprout through compost.

Dahlia plants after a frost
photo: Martha Stewart Blog

Straw mulch
photo: Love’n Fresh Flowers

Digging Dahlias to Store Over the Winter

There is always a chance we will have a particularly cold or wet winter and your tubers will get too soggy or freeze. If you want to be absolutely sure that your tubers survive, you may want to dig and divide them.  Another reason to dig and divide is to increase your stock of tubers. One single tuber planted last spring can grow into 5-10 or more viable tubers for growing or sharing next spring! 

Tubers and stalks get woody in storage, so it’s easier to cut through the stalks in the fall if you plan to store the tubers indoors for the winter. However, you can also dig and divide tubers in the spring. 

Dig under the tuber clump with a spading fork, gently tipping the clump up to avoid damaging the necks of the tubers. 

Wash the dirt off the clump with a spray nozzle, especially from the crevices where the tubers join the stalk because that is where the growing eyes are located, as pictured here. 

Each tuber must have a growing eye to be viable and grow a new dahlia plant. Eyes may look like small white bumps and be difficult to see. Storing the tubers in a medium like moistened - but not saturated - wood shavings or bark, out of direct sun in 50-60 degree temperatures for a week or so may give the eyes a chance to start to swell so they are easier to see.

With a sharp knife or pruners, cut into the stalk vertically between the eyes, leaving each tuber with an eye attached. For large clumps with multiple stalks, divide the entire clump in half or quarters and then divide the tubers from each stalk. Trim and discard excess stalks. Some growers treat their tubers with a fungicide or bleach solution to prevent rot. I have not done this and do not have problems with tubers rotting.

Broken, bruised or damaged tubers, or tubers without visible eyes can be composted. If you are dividing your dahlias in the spring, you can try an interesting experiment: plant these iffy tubers up in a pot and see if they sprout; you just may be pleasantly surprised!

Store the tubers in a medium that retains moisture like sawdust or bark that is about as moist as a wrung-out sponge. They should be dry on the surface and not shriveled. A temperature of 40 degrees is ideal. Plastic bins or cardboard boxes lined with plastic will help maintain moisture. Check on them periodically to make sure they are moist but not soggy or shriveled.

When the soil and weather warm up in the spring and all danger of frost is past, it’s time to take the tubers out of storage for planting. Or, if you didn’t lift and divide them in the fall, you can do it in the spring.  Look for another blog post on planting your tubers out in the garden when planting time comes around again.

If you have any questions about caring for dahlias, let us know in person, by email, or on social media with #heyswansons. We’d be happy to help!

Note: All photos by Denise Read unless otherwise noted.

Tagged: dahlia, dahlia care, dahlias, growing dahlias, digging dahlias, tubers, storing dahlias, flower care

How to overwinter dahlias | Homes & Gardens

As the first frost heralds, it is time to figure out how to overwinter dahlias. Dahlias will continue to flower with their beautiful blooms right up until the temperature drops and the frost arrives. At this point, any remaining flowers, buds and foliage will die immediately. So it is time to start the process of protecting your dahlias from the cold winter weather so that they can regrow next year. 

Just like when learning how to grow dahlias, figuring out how to overwinter dahlias can seem quite daunting – especially if it's your first time. Should you dig them up or leave them in situ? How should you store the tubers? Will they regrow next year? All these questions are very important and the answers depend on both your area and personal preferences.

There are lots of different methods available for overwintering dahlias, which means there will be a little bit of trial and error as you figure out the best way in your specific part of the world. Why not try several different approaches to see which works best for you and your winter garden ideas?

(Image credit: Getty Images)

How to overwinter dahlias: step-by-step

Planning a winter garden does involve preparing more tender plants for dormancy during cold weather. The key thing to remember when learning how to overwinter dahlias is that the tubers should not be left to totally dry out, as you would with bulbs. 'Dahlias require a cool climate, ample air circulation, and being placed in a dark area if they are not being stored in soil media,' says Tammy Sons,  owner of  Tennessee Online Plant Nursery .

  1. The first frost marks the start of the overwintering period. 'Wait until a frost has turned the foliage black, then cut the plant down to about 6 inches,' advises Tamsin Hope Thomson from Amateur Gardening Magazine , 'Then lift the tubers and use your hands to get rid of the soil.'
  2. Having lifted your tubers, the next step is to remove any rotten or dead matter. The tuberous roots should feel firm to the touch and not squishy when pressed. If they don't feel firm or if they look rotten, then remove the rotten material with a clean knife until only healthy tuber remains. Dispose of any unhealthy material on your compost heap.
  3. Some of the tuberous roots may have become detached from the main body – this is okay. The loose tubers can either be disposed of or you can store them with the rest of the dahlia to see if they might make a viable plant the following summer.
  4. Dead tubers appear withered and wrinkled. These also need removing and can go on the compost heap.
  5. 'Do not clean the tubers under a tap; to get water on a tuber at this time of year often spells disaster. Turn the tubers upside down in a crate and leave to dry for a couple of weeks,' advises plantswoman and dahlia expert Sarah Raven in her blog.
  6. Next, label your tubers, recommends Megan Foster, category manager of bulbs & perennials at American Meadows . 'As you build your collection of varieties, you will want to remember which is which come planting time in the spring. Use a marker or tie on a label with old twist ties.'
  7. Once the tubers have dried out sufficiently, it is time to store them for the winter. There are several methods for storing dahlias. The best method for how to overwinter dahlias primarily depends on where you a storing them. If you are storing them in a slightly moist environment opt for paper bags or cardboard boxes as these will absorb the moisture from the air. If you are storing them in somewhere that is drier, then a plastic box or bin bag is a better option as these can be occasionally spritzed with water.
  8. Unlike bulbs they also need to be insulated to keep them warm and prevent them from drying out. You can either cover them in loose, dry compost, sand, vermiculite or straw, or you can wrap each tuber in newspaper. 
  9. Place your tubers in a dry and cool place – unheated greenhouses, sheds, porches or the cellar are all great options. 
  10. Check on your tubers throughout winter looking for signs of rot or severe dehydration. If you spot signs of rot, cut away the compromised material until you are back to the healthy tuberous material. It is also worth moving your dahlias to a drier location to prevent further rot from taking hold. 
  11. Dehydrated tubers are the other challenge when learning how to overwinter dahlias. It is quite easy to tell if your dahlias are dehydrated as they will look shrivelled. If this is the case, occasionally spritz the dahlias with water to help them absorb more moisture.

(Image credit: Getty Images)

Should I split my dahlia tubers before overwintering?

Whether you split your dahlia all comes down to a matter of confidence and knowledge about how to overwinter dahlias. 'If you’re not sure where the eyes are, don’t break apart your tuber clump in the fall before storage. The tuberous fingers of the dahlia are winter sugar and moisture survival supplies for the eyes which are the source of new growth for next spring. If you disconnect the two accidentally, you’ll be disappointed with lack of growth,' advises Megan Foster, category manager bulbs & perennials at American Meadows .

However, if you are certain where the eyes are and that they are still connected to plenty of tuberous fingers, then you can separate the two before overwintering. To do this use a clean knife to cut away the eye and tuber. Then overwinter in the same way you would a non-separated dahlia.

(Image credit: Getty Images)

Can you leave dahlias in the ground?

If you live in an area that have milder winters and very free-draining soil then you can leave your dahlia tubers in the ground. However, this is only suggested for hardiness zones 7 to 10. If you are leaving your tubers in the ground, then there are some steps you must follow to protect them during the cooler months. 

Once your dahlia has succumbed to the frost, leave it for about two weeks to let the sugars go back into the tuber, then cut the stem back to around 6 inches tall. Dispose of the foliage on your compost heap. After this, cover with a mound of deep mulch to insulate the tubers throughout the winter months.  

(Image credit: Getty Images)

Can you leave dahlias in pots over winter?

Although dahlias aren't candidates for the best winter plants for pots and borders, yes, you can leave dahlias in pots over winter. One of the beauties of growing dahlias in a pot is the flexibility that it offers. When in bloom, you are able to move your plants around your garden so that the most show-stopping displays are always front and center. 

This flexibility continues when figuring out how to overwinter dahlias that you have grown in pots. When overwintering pot grown dahlias, it is vital that they are sufficiently protected from the cold weather. 'It is important to create storage conditions that somewhat mimic dahlia tuber’s natural habitat under earth in a drier climate and non freezing latitudes,' advises Megan Foster. 

If you can move your pots inside, into a cool but frost-free, dark and dry place – like a garage, unheated greenhouse or shed – then do so. If you do not have a space to move your pots to, then cover with a mound of compost or manure, as you would with dahlias left in the ground. You can then cover your pot with frost-fleece to help protect it and move it to an area where it will be protected from rainfall.

Allow the pot to partially dry out. It is important to not let them dry out completely, but equally don't water regularly as you would during the growing period. Water as frequently as you would a cactus – a cup of water every month or so is sufficient. 

(Image credit: Getty Images)

How to overwinter dahlias in Saran wrap

Overwintering dahlias in Saran wrap is a fairly new method for overwintering dahlias, however, it has received a great response. In fact, it is now the go-to method for the American Dahlia Society, having moved away from vermiculite and plastic bags.

Start by lifting your dahlias, as you would for any other method, and clear them of soil. Whether you treat your dahlias with an anti-fungal treatment to ward off rot is a personal choice, and should you not wish to, you can simply skip this step. However, it will offer greater protection for your dahlias over the colder months.  

'Add a very small amount (around a tablespoon) of powdered sulfur to 3 cups of dry vermiculite in a gallon size ZipLock bag and mix thoroughly' suggests Marian Mandella, Bernard Mandella, and Richard W. Peters, M.D, experts at The American Dahlias Society . Then add your tuber and shake lightly so that your dahlia tuber is coated – 'a very, very light coating should be best.' 

Having done this, set your dahlias aside in a crate to dry overnight before wrapping. 'Tear off a sheet of plastic wrap about 20 or more inches long and lay it flat on a level surface. Place a tuber on one end and roll the plastic wrap over one complete turn. Lay another along side and roll again. Be certain that no tuber is touching another; plastic wrap must separate all tubers.' Once you've wrapped your dahlias, fasten with masking tape and label with the dahlias's name before storing in a dark and dry place at around 40°F for winter.

(Image credit: Getty Images)

What month do you cut back dahlias?

Cut back dahlias in late fall – October and November, however don't cut them back immediately. 'Leave the stems to go black from the first frost for approximately a two weeks to allow the sugars to go back down the stems to feed the tuber. Then cut the stems off just below ground level,' advises PL gardening expert Leigh Clapp.

You need to do this however you are overwintering your dahlia tubers as it will increase their likelihood of survival and the extra energy it provides will help them to restart growing in the following spring. 

(Image credit: Getty Images)

When to dig up dahlias and how to store tubers in winter at home

Dahlia is a favorite of many gardeners, its luxurious flowers of different shapes and shades can decorate any area. Despite the fact that the plant is native to South America, keeping dahlias for the winter is not difficult if you create the right conditions.

In order for dahlias to bloom in the new season, it is important to arrange a warm winter for the tubers. You can’t leave them in the soil, because. after the first severe cold, the plants turn black and die.

In August, when dahlias are in full bloom, you need to stop feeding, providing the plants with rest. Just at this time, the formation of tubers and their storage of nutrients begins.

Autumn care for dahlias - preparation for winter

Now let's figure out how to prepare dahlias for winter. In early September, the bushes need to be fairly high up (approximately 8-12 cm high). This will make them more resistant to wind and cover the base of the trunk, which means that the tubers will grow strong. In general, the procedure can be carried out at the end of summer.

Dahlias should be watered sparingly so that excess moisture does not lead to infection. Weak stems without buds, lower leaves, as well as drying flowers should be cut off to speed up the formation of new buds.

When to dig up dahlias

Dahlias are dug up in the middle lane and Moscow region in mid-late October, depending on the weather. It’s good when, by the time of digging, the heaped tubers have already withstood several weak frosts - this will harden them and help them to endure wintering at home without any problems.

So how do you keep dahlias in winter? First of all, cut off all the stems with secateurs, leaving stumps 10-15 cm high. If you cut the stems lower, there is a danger of infection entering the tubers. Also, if the height of the “hemp” is insufficient, water can flow into the tubers, and they simply begin to rot.

Then carefully loosen the shrub and dig in with a fork to loosen the surrounding soil. It is also better to raise the dahlia with a pitchfork, trying not to pull the stems. If the weather permits, then the dug tubers can be left to dry in the garden for several hours, after which the earth must be shaken off and the tubers themselves carefully examined.

Weak and diseased tubers are discarded, and strong tubers are thoroughly washed with water. Cut long roots with scissors

It is better to divide the tubers strictly before planting, otherwise they will lose a lot of moisture during the winter.

Treatment of dahlia tubers before winter storage

To prevent diseases, treat washed dahlia tubers with a fungicide, such as Fitosporin. Prepare the solution according to the instructions and soak the tubers in it for about an hour. Instead of fungicides, you can also use a pink solution of potassium permanganate. Keep the tubers in it for about 30 minutes.

Then tag the tubers with variety names. If the variety is unknown, you can focus on the size of the bush, the shape or color of the flowers.

The next step in preparing dahlias for winter is drying the tubers. To do this, you need to choose a dark, cool place and put the bushes with the tubers up so that the moisture accumulated in the stems flows out and the tubers do not subsequently rot.

How to store dahlias in winter at home

Dried dahlia tubers are placed tightly in plastic buckets or boxes and covered with dry sand or sawdust, leaving the tops of the stems with tags uncovered. To prevent sand from spilling out of the box, you can lay a bag of sugar on the bottom, and then lay out a layer of newspapers.

Gardeners differ a little on how to preserve dahlia tubers, with some using wet sand instead of dry sand. Everything is individual here, and if the tubers were dug out in dry weather, and then not soaked in a fungicide solution, then sand or sawdust is really better to moisten.

There are several other ways to store dahlia tubers in the winter:

How to keep dahlias until spring? Choosing a storage location

The optimum temperature for storing dahlias in winter is 3-6°C, humidity is 60-70%. At lower temperatures, the tubers will freeze, at high temperatures, they will begin to germinate. There are several places where plants will feel comfortable until spring.

Cellars and cellars . They are characterized by high humidity and low temperature. The tubers will not suffer from drying out and will not germinate ahead of time. This is the best place to store dahlias!

Subcol . Here, the humidity is lower than in the basement, and the temperature can be slightly higher, often there is stagnation of air. Therefore, it is recommended to turn on the fan in the room several times a week.

Refrigerator . A suitable place for a small number of dahlias. Put the tubers in a perforated bag and cover with sawdust. Check regularly for rotting. For storage, the lower or middle shelf is suitable, as well as a compartment for vegetables.

Glazed balcony . Choose the darkest place and put a box of tubers in it. If the temperature starts to drop, cover the crate with old blankets or clothes. In frost, it is better to transfer the tubers to the room for a while.

Periodically check the tubers for signs of decay.

Protect the dahlias from being eaten by rodents. It is better to use fast-acting poison baits or ultrasonic repellers. There is evidence that mice and rats do not tolerate peppermint essential oil. To scare away, soak paper napkins with oil, put in glass jars without lids and place them in different corners of the room or near boxes with tubers. Once a week, change the napkins for new ones.

Is it possible not to dig up dahlias for the winter

Novice flower growers often ask themselves the question: is it necessary to dig up dahlias for the winter, is there any way to avoid this troublesome procedure? Unfortunately, these plants are very afraid of the cold and will not survive until spring. But there is a way out. If storing dahlias in winter is problematic for you, grow them as annuals. Or you can dig up only the most beloved and expensive varieties, and re-plant the rest in the spring. The decision is yours!

Storage of dahlia tubers is not difficult, but responsible, because you need to look after the "wintering" plant: check the tubers, regulate the temperature regime. The dahlia will not remain in debt, but will delight you with its lush bright flowering!

Articles you might also be interested in:

when and how to dig, cut, what to do with sick, frozen ones, how to prepare for storage and store

An important question arises for beginner flower growers who grow dahlias when to dig up these beautiful flowers. There is no doubt that this large multi-layered and surprisingly beautiful flower has many to their liking. But in order to enjoy its beauty for as long as possible, dahlias need to be dug up for the winter.

Digging up dahlias is a very responsible business, because it depends on this, and also on compliance with the rules for storing dug tubers in winter, whether they will bloom next year.

Contents

Digging up dahlia tubers in autumn

Before digging up the roots of a flower, it is necessary to read the recommendations of specialists.

Before digging up dahlia tubers for the winter, there are a few important things to consider:

Obviously, tubers can only be dug up after the plant has completely faded and shed all the flower stalks.

An important condition for observing the correct organization of harvesting dahlias and their subsequent storage throughout the winter is the determination of the correct period for harvesting tubers. Before harvesting the tubers, it is necessary to stop feeding the plant with various fertilizers. The end of the growing season is not necessary to fertilize the flowers, especially if they are dug up for the winter.

When to dig up dahlias also depends on the variety of the plant. Tubers of a large number of varieties of these beautiful flowers begin to form in early spring. But their final ripening occurs only towards the end of the summer flowering season. It follows that a longer stay of plant tubers in the soil will have a positive effect on the process of their formation, and hence the quality of storage of dahlia roots in winter.

In most of the territory of our country, at the end of the summer period, light, slight frosts occur. Frosts, although small, just a couple of degrees below zero, but such an insignificant decrease in temperature indicators can destroy the flowers and leaves of the plant.

Those areas of dahlias that have suffered from the cold must be cut off immediately, so that the plant has the opportunity to delight its owners in the future with beautiful flowering. The tubers at this time will direct all their efforts to enhanced ripening and a kind of preparation for winter storage. This process will continue until severe frosts.

The procedure for digging up dahlias can be carried out immediately after the first hard frost occurs.

Dahlias: when and how to dig (video)

Digging up dahlias for the winter

Just before harvesting dahlias for the winter and getting ready to germinate them, the grower needs to do some preparatory work.

First of all, you need to pay attention to sick plants, weakened over the summer and not blooming or blooming weakly. They must first be isolated from other plants. To do this, you need to dig up the infected plant directly with a clod of earth adjacent to the roots and burn it. It is no longer possible to cure such a plant.

It is believed that shortly before dahlia roots are dug up, all leaves and stems should be cut off from plants. But it is important to do it carefully and correctly. Pruning too short can cause flower tubers to rot. This can happen due to the fact that water will flow into the stem. If it is decided to dig up dahlias according to this method, then each individual flower stem must be covered with ordinary food foil.

So, the stem should not be cut too short, otherwise the tubers will not survive in the winter. The length of the stem above the soil surface should not be shorter than 10 cm. This, by the way, will facilitate further work with tubers. It is important at this time not to forget to make a note about the flower variety. You can hang a tag with the name of the dahlia variety on the cut stems.

When digging up dahlias, it is important to be very careful not to damage them with a shovel. And the necks of the tubers are fragile. This becomes noticeable even in the process of extracting them from the soil.

When to get dahlias out of the ground? It is better to do this in the morning, since the dug out tubers require drying before harvesting for storage and subsequent germination. This procedure will slightly strengthen the roots of the flowers.

In order to remove the dahlia root from the ground without unnecessary damage, it is first dug around. This will trim the long roots and keep the tubers intact . Carefully pulling the tubers out of the soil, you need to turn them down with stems and dry for some time under the sun. The roots are then rinsed under running water to avoid contamination and dried again. Only now the prepared tubers of plants can be removed for storage and further germination.

How to store dahlias: is it necessary to harvest

Dahlias must be stored properly in winter. It is recommended to put the roots in a cloth bag beforehand and put them on the bottom shelf of the refrigerator for 4-5 days.

This method will allow the process of corking of the skin to begin, this will subsequently allow moisture to remain in the tubers during the winter.

After that, you can remove the tubers to a dark, cool place, such as a basement or cellar, for storage and further germination.

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