The Complete Beginner’s Guide to Growing Dahlias

Dahlias are available in a huge range of different colors, shapes and sizes but they all have one thing in common; they’re truly some of the most showy flowers around.

Even better, dahlias tend to flower for long periods of time, often reaching their peak in very late summer or even later. By September and October many varieties are still flowering heavily, providing a much-needed explosion of late season color.

But growing dahlias is rather different to many other garden plants; where do you begin?

Understanding Different Types of Dahlias

Getting started with dahlias can be an intimidating prospect. After all, there are so many different varieties of dahlia that it makes sense to do some research in advance. In this manner you can get an idea of what size of plant would look best in your garden, and what types of flowers you prefer.

Visiting your local garden center can work, though appreciate that any flowering plants may soon start to fade. In addition, of course, if you’re looking at buying dahlias that are already in flower, you’ve really already missed the season. A better idea is to do your research during the winter and early spring; in this way you’ll be able to get organized in plenty of time for the growing season.

Do some searching online or visit sites like Pinterest to get your eye in and find the types of dahlias you’d like to grow. Consider, for example, whether you find the pompom or cactus-type flowers more visually appealing, and consider both the ideal height and your preferred colors. Specialist dahlia breeders can also be a great source of inspiration, helping you to narrow down the choices on offer.

How to Buy Dahlias

There are typically three main ways to buy dahlias. These are:

Seeds

A limited number of dahlia varieties are available to grow from seed. Starting off with seed can be the cheapest way to grow dahlias, but the range of seeds on offer tends to be reasonably small. In addition, dahlia seedlings can take some time to really get going.

Having grown a number of dwarf dahlias from seed myself I find that you’re lucky to get more than a few flowers in your first year. It’s really in their second season that the plants really take off and put on a full show of blooms.

In short, starting dahlias from seeds is possible; and it’s a very cheap way to get started growing dahlias. That said, you’ll need to be patient as you can’t really expect much in their first year. As a result, while I’m not against planting dahlia seed, I would recommend supplementing your seedlings with other growing methods for a quicker display.

Tubers

The most common way to grow dahlias is through the purchase of tubers. These are odd swollen roots that look almost alien-like when they arrive. Planted up in moist compost in the spring, however, they will quickly make use of all that stored energy and start growing rapidly.

The bigger the tubers you purchase, the bigger the plants you can expect later in the season (and the more blooms too). That said, buying dahlia tubers can be an expensive proposition, particularly if you have your eye on some of the rarer or more showy varieties. You must therefore be willing to invest.

In short, growing dahlias from tubers is probably the best possible solution. While the upfront costs are more than growing from seed, you’ll end up with much larger plants a better display in year one. Thereafter your plants will continue to grow and divide, providing you with ever more dahlia flowers to enjoy.  

Plants

In season, it is also possible to grow live dahlia plants from garden centers and nurseries. This tends to be the most expensive way to buy dahlias, and if you end up purchasing a plant already in bloom then you may not enjoy many more flowers before the season ends.

While there is nothing wrong with buying dahlia plants to pop in your garden, this method is recommended for more impatient gardeners who want a near-instant show of color. For the rest of us, willing to plan ahead, purchasing tubers is likely to be the perfect middle ground between cost and impact.

Dahlias are a Long Term Investment

When properly cared for, dahlias are perennial plants, meaning that they will flower year after year. In time, you will find that your plants get bigger and bigger, and with their increased dimensions so you can also expect more flowers. Like a fine wine, therefore, dahlias are something that will improve with time.

Whilst dahlias can be expensive to buy initially, therefore, appreciate that you’ll be enjoying your plants for years to come. What is more, if you look after your plants properly then you’ll find them multiplying in your garden, providing you with more color each season.

Getting started with dahlias can therefore be thought of as a long-term investment. While the start-up costs might make you wince, it’s likely to be a one-off cost that pays you back many times over in the future.  

Planting Dahlias

Dahlias can be quite sensitive to the cold, so you’ll want to avoid planting your tubers out when frost is still on the ground. In many parts of the northern hemisphere, therefore, you’ll most likely want to wait until April or May to plant out your dahlias.

If you want to get a head start then I have found that planting my dahlia tubers in tubs, then placing these into my greenhouse gets them off to a good start. In this way I can kick-start my dahlia growing season weeks before I might otherwise manage to plant them outside. This has an added bonus that when it really is time to put my dahlias outside the plants are already fit and healthy, making them far less appealing for pests.

I tend to plant my dahlia tubers around 4 inches deep. I have found that the tubers can take time to show signs of life, and if you’re not careful you can forget all about them. Even worse, the young leaves of dahlias seem to be particularly appetizing for slugs and snails, who regularly chew my dahlias all the way back down to ground level.

Rather than the “plant and forget” route, I therefore recommend two additional steps. Firstly, use a plant label to carefully mark where each tuber is planted. For ease later on in the season, try to include the exact variety too, so you can keep yourself organized.

Secondly, take steps to prepare your fresh dahlia shoots from pest damage. You may decide to dose the soil around your dahlias with slug pellets, but for organic gardeners a suitable alternative is to cover the soil. If you have the money, consider buying some attractive garden cloches to use. If you’re on a rather tighter budget then cut the bottom off some old clear plastic soda bottles and position these over your tubers.

These coverings will of course need to be removed as your dahlias grow, but at least it offers them some additional protection for the first few weeks of the season.

Protecting Your Dahlias

In my experience, the larger your dahlias get the less appealing they become to slugs and snails. That said, you may well find that another problem soon starts to make itself felt. Many varieties of dahlia get surprisingly tall; many growing to over a meter in height. As a result, larger dahlia bushes can start to “wilt” if they are not supported. Some strong winds can even snap large dahlia flower heads clean off the stem.

Before your dahlias get too large, therefore, it can be a good idea to to offer them some support. This is easiest early in the season, as by the time your plants get really large and truly need some support, it can be much more difficult actually adding it without causing damage.

There are a huge range of possible options when it comes to supporting your dahlias. One of the easiest is simply to place a thick garden stake next to the main growing stem of your plant, and to use green garden twine to gently tie the main stem to the stake.

For more creative gardeners there are a whole range of possible alternatives, from making rustic plant supports using hazel twigs, through to specially-designed plant supports available from many garden stores.

Overwintering Dahlias

Possibly the touchiest subject when it comes to growing dahlias is what to do with them over winter. As we have mentioned previously, dahlias tend not to do very well in cooler conditions. This is especially so when the weather is wet, whereupon dahlia tubers can rot. Bearing in mind the cost of such tubers, and the time you’ve already invested in them, you may choose to take steps to protect them.

The most time-intensive (but effective) solution is to dig up your dahlia tubers at the end of the season. Place them somewhere dry and frost free (such as in your shed) for a few weeks so that the tubers can dry out. Then plant the tubers in tubs of dry compost and keep them in a frost-free place during the winter months. In spring, you can begin watering the tuber once again, at which point they should explode back into life.

Of course, this is an awful lot of work – especially if you end up with quite a collection of dahlias. Some gardeners therefore take a slightly more relaxed view of things. Rather than digging up their tubers, they simply add a thick layer of mulch on top of the soil, to help keep out the worst of the cold.

There are even those who successfully growing dahlias year-in, year-out who simply leave their tubers to cope in winter. While this is the easiest option of all, this does of course need to be balanced against the odds of damage to your tubers.

Possibly the best way to decide how to overwinter your dahlias is to ask other gardeners in your area what they do. If they’re all happy to leave their tubers in the ground and enjoy a great crop of dahlias each year then it may well be safe to try the same thing. If, however, they all dig them up each winter for safety then this might be the best option.

If in doubt, I would suggest taking the safest route of storing your tubers in a cool but frost-free building. While this does add to your gardening chores somewhat, it’s also the safest way to make sure your beloved dahlias live to see another growing season.

Wondering how to grow dahlias in your garden? If so this guide to growing dahlias will show you how to get the best display with the minimum of effort. Well worth a read!