3 Reasons to Plant Dahlias in Indoor Pots (and How to Do It)

Between you and me, I was eager to start my dahlias as soon as I posted this overwintering article. But as I write this, my yard is still covered in an unexpected blanket of snow in mid-March. And our estimated last frost day is the end of April. So what should a gardener do if they have a compulsion for dahlias?

Of course, start potted dahlias indoors!

It’s barely March, but I dream of blooming dahlias.

3 reasons to grow potted dahlias indoors

I plan to transplant my dahlias outdoors in the garden in May. So I could have waited until early April to start my indoor dahlias. But I choose to do this task now for three reasons:

I want my dahlia tubers planted and out of the way before I start planting knee-deep vegetable seeds;

My growing season is quite short, so I try to anticipate it by putting as many plants indoors as possible.

Pom-Pom dahlias, like this ‘Cornel Brons’, are some of my favorites.

I plan to take cuttings from these dahlia tubers before bringing them to the garden. The high quality organic tubers I bought were expensive (no regrets!), so I try to get the most out of my dahlia. These cuttings will also need to “take” and sprout before transplanting them outside (which will likely be early June).

How I Start Potted Dahlias, Assembly Line Style

When I plant potted dahlias, I organize all my materials in a systematic way, creating a conveyor belt on my back porch. I like to work this way because it’s easier to know which varieties of dahlia I’m planting.

Unboxing my order of dahlias feels like Christmas in March.

My curiosity and appetite got the better of me when I ordered the tubers, so I bought six varieties of dahlias, from the smallest ones suitable for containers to the prettiest dish, the “Café au Lait”.

This is how I start my dahlias indoors:

Step 1: Write and organize the labels.

Isn’t this the last stage of planting? Usually yes! If I planted anything else, I would write and stick the labels on the pots last. But since I grow six varieties of dahlias, I need to know which is which. And once you open the bag, one potato-like tuber looks like the other. So, so as not to be overwhelmed, I prepare the labels before literally getting my hands dirty.

This year I will start with the following dahlias:

Dahlia Latte‘ – a classic variant of the flat plate in very pleasant mocha and peach tones;

Dahlia ‘Lavender Perfection’ – another table plant which, despite its name, is a little pinker than lavender;

Dahlia ‘Manhattan Island’ – red like red but may be with a creamy yellow centre.

Latte (left), Lavender Perfection (center), Ace of Hearts (right)

Dahlia ‘Festive Impression’ – a small, bright red dahlia with a creamy yellow border along the inner petals. It is suitable for growing in containers and small spaces.

Dahlia ‘Freya’s Love’ – a small fuchsia dahlia with fine white stripes on the edges of the petals;

Dahlia ‘Ace of Hearts’ – a soft pink dahlia with a fluffy neck and a bright yellow bud in the middle;

All I see is potential!

The first three dahlias on the list grow tall, both in terms of flower size and stem height.

The last three were put together by the seller in a “balcony pack”. The flowers are small, but very colorful, while the stems are also short. If I wanted to, I could grow these three in pots. (I have not made my decision yet.)

Step 2: Clean the tubers.

I was tempted to skip this step because it’s something I do instinctively. Until my husband, who was kind enough to take photos of my artisan hands, asked me a simple (simple for me) question.

There were a few loose little tubers in the bag, so when I put them aside, he asked, “Aren’t you planting them?” He wasn’t, but he had to explain why. And then I thought every novice dahlia grower would face the same dilemma. Plant loose tubers or not?

Before repotting the bulbs, remove any broken, dry or rotten bulbs.

Let’s look at the anatomy of the structure of a dahlia tuber. You have the old stem (which goes up when repotted), the roots (which go down) and between a collar and a clump of tubers. New shoots emerge from the collar, the part still attached to the main stem. The sprouts first appear as small “eyes” around the top of the tuber (which is also the bottom of the stem).

Most of the tubers were dormant, but I was still able to find a small eye on one.

So there’s a good chance that nothing will grow tubers that are loose in the bag (and have no collar, so no “eyes”). That’s why I prefer not to put them in pots.

If you want to try this, you can store them in a paper bag and plant them directly in the garden in June. But don’t expect miracles.

The right way to plant a dahlia tuber.

I bought the tubers from a reputable seller, so I’m sure they’ve already done this inspection and done their best to send me quality material. But some things are still overlooked. So when I inspect the bulbs, I also remove any dry, rotten, or soggy growth. A simple pinch test will suffice. If the plant material seems too soft or hollow, it may no longer be viable.

Cut dead or damaged material.

This step is especially important if you are storing the bulbs yourself during the winter months. If the tubers get too cold or freeze, their cell structures can break down and you end up with dry, papery tubers that are useless.

On the other hand, if they had been kept in a humid container with insufficient airflow, they could have become soggy, mushy, and rotten. These tubers will also not be viable. Therefore, it is best to remove and discard these tubers before planting them.

Step 3: Find the right size container.

Look at the size of the tuber structure, not the size of the stem.

This may not seem like a big deal, but it is. If the container is too big, we will tend to fill it with too much soil. And at this stage, when there are no roots to absorb moisture from the soil, this choice is problematic.

It’s okay if the tubers are a little tight, but don’t squeeze them too hard so they don’t fall out of the container. The crown should have enough space for new roots to grow.

This container was definitely too small. Back to the shed.

So before deciding which dahlia wreath goes where, I played a game of musical chairs with my containers.

Placing the pots in the labeled bags made it easier to track the tuber varieties. You may have noticed that this was a task I was very meticulous about while repotting.

It’s like a disco game with musical chairs.

Step 4: Prepare the soil.

Now that the tubers are in order, it’s time to start playing in the mud. I bought a soil suitable for cooking and making bulbs. But since I’ll be keeping these pots indoors for at least six weeks, I wanted to make sure the soil was well-drained and loose enough.

Perlite, bark or coconut fiber improve soil drainage

The containers are not exposed to the sun and do not have much air circulation inside, two factors that slow down the evaporation of water, so it is essential that the soil does not retain too much water .

So I added another handful of perlite (about 15-20% of the total) to the potting mix. If you think the potting soil you are using drains well, you can skip this step.

Step 5: Plant your dahlia tubers in the ground.

Hold the bulbs upright by the stem and fill.

Start by adding a few centimeters of potting soil to the bottom of the pot. Not too much (for fear of moisture buildup and rot), but just enough to give the roots room to grow. Then place the bulbs in the container and start adding more potting soil while supporting the crown by the old stem.

This one needs a little more potting soil.

Knock the bowl a few times to make sure the dirt settles and there are no large air pockets. But do not manually tamp or compact the soil around the tubers.

Fill it with soil until you can no longer see the tubers. They don’t need to be buried too deep, so aim for an inch or two of soil above if possible.

Refill if too much dirt settles.

Don’t worry too much about burying every inch of the crown if you’ve misjudged the pot size. The fact is that most of the crown comes into contact with soil moisture to start the germination process.

Some stems will stick out. This is not a problem.

I left my tubers fairly close to the top (but still covered) as I plan to take cuttings as soon as there are enough sprouts.

I followed the varieties I planted, always working in their respective pockets.

You may notice the old, dry stem protruding from some of the crowns. It is good too. You can cut the stem to ground level or remove it when you plant the dahlias in the garden later. I left it on because it was easier to handle the dahlia wreaths.

At the risk of sounding like a broken record, I feel it my duty to remind you to put your labels on the jars.

The final touch.

Step 6: Water lightly.

If you started with moist potting soil, you can skip this step for now. The soil in my pot was quite dry, so I had to water the tubers. Water lightly and let all the water drain out.

Stop watering the pots until you start seeing sprouts. And even then, if the soil still seems damp, water very little (or not at all).

A quick rain will do. Do not soak the tubers for a long time.

Step 7: Keep your pots frost-free.

You may have noticed in the photos that I started making these planters outside on my back porch. But I brought all the pots indoors and put them in my indoor tiered greenhouse.

I expect the dahlia tubers to sprout in three to five weeks. In general, smaller, early-flowering dahlias germinate faster than larger, late-flowering dahlias.

I brought the containers inside.

Indoor dahlia tubers don’t need a lot of light until they start to sprout, but they shouldn’t be colder than 70°F (21°C) for faster germination. And they should definitely be in a frost-free place.

So even if you are growing them in a cold room, greenhouse or greenhouse, make sure that the temperature does not drop too low.

You don’t have to worry about getting enough light until the shoots start to grow. But once the eyes have grown, you should place the dahlia pots on a windowsill or where they can receive more light.

Starting potted tubers may seem tricky for a dahlia beginner, but I can promise you it’s worth learning the first time around. And once you’ve done that, it can quickly become your favorite way to grow dahlias.