In 2017 my garden goal was to grow more flowers! Dahlias have always been one of my favorite flowers (well, I guess they are second behind ranunculus), so I decided to buy my very first tubers and give it a try. To my surprise, the dahlias tolerated our triple digit summers, were very low maintenance, and made the prettiest cut flowers! Below I’m sharing my favorite tips for growing dahlias.

How to get started with dahlia tubers

My number one tip for growing magnificent dahlias is starting with magnificent tubers. What is a dahlia tuber? A “tuber” is formally defined as an extremely thickened underground stem serving as storage for food and being the source from which new buds arise. More simply, a dahlia tuber is like a bulbous root you plant deep in the ground.

If you are looking to start growing dahlias, I would encourage you to start with just a few varieties, and start with tubers. Starting small really helped me focus on growing them successfully. Also, dahlia tubers grow as a “copy” of the parent tuber, which is why we know what the blooms will look like when we purchase from a vendor. Additionally, see my note below about starting dahlias from seed.

See my list of places I have purchased tubers & seeds → HERE

Did you know?

Dahlias are a fantastic garden investment. If treated properly, their tubers will last year after year—they will even grow large enough to separate into multiple tubers. In warmer zones, generally zones 8-11, dahlia tubers can be left in the ground during winter whereas colder zones will need to lift tubers out of the ground for storage during winter (this is a whole other topic). Regardless dahlias can be a part of your garden for years.

Dahlias can also be a wonderful addition to pollinator gardens. I know you came here for tips for growing dahlias, but I also wanted to note that dahlias can also be wonderful sources of food for bees and pollinators. For bee-friendly options, include dahlias that have open centers, such as the ‘Mystic Illusion’ dahlia HERE. Update: while experimenting with growing dahlias from seed, I’ve also found that the majority of seed-grown dahlias are very bee-friendly.

When your dahlia tubers arrive

When you receive your dahlia tubers, please note that they can come as one tuber or as a clump. Do not separate the clump because not every tuber in the clump will have an “eye.” Additionally, if you break a tuber off and it doesn’t have an eye, it won’t grow. *see photo below

Soil Requirements for Growing Dahlias

It is rumored that if you can grow tomatoes, you can grow dahlias. I found this to be both helpful and true! Why? Well, dahlias have a lot of the same soil requirements as tomatoes. For instance, dahlias like fertile, rich soil with good drainage. Dahlias do not like heavy, clay soil. In fact, I would highly advise you to plant some dahlias in the same area you would grow tomatoes. For example, this is one reason I chose to try growing dahlias in my raised beds. The drainage is excellent, and I usually am pretty diligent when it some to caring for my vegetables, so the dahlias have a better chance at survival simply by proximity.

Dahlias also need full sun. I tested this out one year, and tried growing one in shade. It grew extremely slow and barely put off a couple blooms. Not a happy dahlia!

To prep a garden bed for dahlias, I follow the same procedure that I’ve shared in Amending Your Soil Organically, and definitely sprinkle in bone meal (as discussed in the “organic amendments” section). Dahlias are flowering tubers that really benefit from the boost of phosphorus that the bone meal provides.

How & When to Plant Dahlia Tubers

Plant your dahlias tubers in Spring. When you go to plant the dahlia tubers, make sure that all danger of frost has passed. Dahlias are not frost tolerant and the soil needs to stay warm for them to start growing (ideally around 60 degrees F). For example, I waited until March to plant out my dahlia tubers last year due to our prolonged Winter weather. Wherever you are gardening, just be aware of your last frost date and plant out your tubers afterwards. Remember to choose a location with full sun.

Dig a hole about 6″ deep and plant your dahlia tubers. Since dahlia tubers can come in many shapes and sizes, I like to say that the eye (or sprout) of the dahlia ends up being less than 4 inches from the surface of the soil.

If planting many dahlias in a row, space them anywhere from 12-18″ apart. Since we do not have humidity in my area, closer spacing is not as much of an issue. If you have high humidity, you might want to space them farther apart to provide adequate airflow.

Important: do not break your tubers! Be sure to make your hole large enough to place the tuber inside without breaking off pieces.

Cover with soil.

Unless you are expecting a rain, water the tuber until slightly moist immediately after planting but that’s all—you don’t have to start regular watering until green has emerged. Since I planted my tubers in my raised beds, they naturally received residual water from my raised bed irrigation. Basically, as the surrounding seedlings were sprayed with water, the tubers also received a slight amount. This was okay. The most important thing is to never soak your tubers, bulbs, etc. because they can rot in the ground before even starting to grow, but I think watering at least once after planting the tubers (and residually if that’s how your irrigation works) is completely fine.

I’ve got a full article on my Watering & Irrigation Basics if you want to know more about the different options and setups available. 

The dahlias pictured above are ‘cafe au lait’ a true romantic dinnerplate dahlia and favorite of many floral designers. I bought my ‘cafe au lait’ tubers HERE.

Staking Dahlias for Support

While small varieties of dahlias do exist (like this beauty with dark foliage), most plants grow over 3 feet tall and get top heavy. For dahlias that can get large, secure a wooden stake in the ground at planting time for support. I later will use twine to tie the main stems in. You can also make a cage by placing four stakes around the tuber and using twine to wrap around the stakes and form a “cage.” Tomato cages also work. There are really lots of options, but just be aware that support will most likely be necessary.

Learning to Pinch or Top Your Dahlias

The practice of pinching or topping the main stem of your dahlia plants can help them become bushier and produce more stems for flowers. This is one tip for growing dahlias that many professional growers and flower farmers do because it helps plants stay a more manageable size and will create lateral stems that will, in turn, give you additional flowers.

Before I continue, I’d like to note something for all the beginner dahlia growers out there: you don’t have to pinch your dahlias. My first year growing them, I had never even heard of it, so I didn’t pinch mine and I still got blooms all Summer on very happy plants. Some gardeners have told me they simply don’t want to devote the time to do it, while others aren’t growing for competition/sale and just let their dahlias be a part of the natural garden landscape. Either way, I just want you to know your dahlias won’t be ruined if you don’t pinch.

Here is how to pinch or top a dahlia plant: when your dahlia reaches about 10″-12″ tall, simply chop off the top with pruners down to a lower leaf node. See the diagram below for where to cut. That being said, I play around with topping my dahlias. I’ve noticed that our long growing season in Southern California means that I can even let the main stem flower first, cut it back to lower leaf nodes, and then laterals will grow later on for a Fall flush. You can also go with a more “instinctive” approach—if a stem is looking thick (ie. like a broomstick), top it, but if the stems are looking small and bushy already, leave it!

Additional Tips for Growing Dahlias

My dahlias liked a kelp or fish fertilizer. About once a month I would use organic liquid fish fertilizer, diluted with water per the instructions. You can also use a fish & kelp emulsion.

Dahlias are not drought tolerant. They like the soil to be kept evenly moist. Sometime our summer temperatures get into the triple digits, and I could tell that it forced the plants to create smaller blooms, but they did not die! If possible, try and shade your dahlias on an outrageously hot day or interplant them in a design that keeps the soil and roots shaded for better water retention and protection.

Dahlias like to be picked! The more you cut the flowers, the more the bush is encouraged to grow and put out flowers. Dahlias do well in vases, and whenever I give them as gifts the recipients are always mesmerized by how beautiful they are.

I made a video (below) of how I plant my dahlia tubers for all of you visual learners out there. Hopefully you have enjoyed these simple tips for growing dahlias! 

Winter Storage & Overwintering

At the end of summer your dahlias will start to fade or will be hit with a frost that causes them to wilt. Sadly, that means the end of dahlia season. If you live in a zone that does not get snow or does not heavily freeze (typically zones 8 and up), you can actually leave your dahlias underground through Winter. Simply cut your dahlia stems down to the ground and cover with a good layer of mulch for the Winter season. Water overwintered dahlia tubers sparingly while they hibernate in the ground because they are susceptible to rot. 

If you live in a garden zone that requires you to lift and store your tubers over the Winter, I recommend consulting a gardener who has actually practiced doing this. Since I garden in California, I have never had to do this. It’s possible that the company you purchased your tubers from has recommendations.

I hope this simple guide has inspired you to start growing dahlias! You can also view extra dahlia planting videos, overwintering tips, and more in my Instagram highlights entitled “Dahlia Tips.”