How to Plant Dahlia Tubers (Dahlias 101 – Week 2)

Welcome to Week 2 of my Dahlias 101 series! If you missed it, you can read Week 1 here.

This week we’re diving into the details of how to plant your dahlia tubers so they grow into strong, healthy plants.

And if you haven’t ordered your tubers yet, now is the perfect time. Four varieties have already sold out, and once we get closer to planting season, things tend to move quickly.

You can browse the varieties still available here.

When Should You Plant Dahlia Tubers?

Dahlia tubers should be planted after your last frost date in spring, once the soil has started to warm up.

Where I live in southeast Pennsylvania, that’s usually around Mother’s Day, which is the same time many gardeners plant tomatoes (remember the tomato rule?).

If you’re unsure of your frost date, you can use an online tool to look up your average last frost date.

Tip: Create a reminder for yourself now. Put “plant dahlias” on your calendar so you don’t forget.

Where Should You Plant Dahlias?

Dahlias grow best in full sun, which means 6–8 or more hours of sunlight per day.

They will tolerate partial sun (4–6 hours), but plants may produce fewer blooms.

A location on the south or east side of your house often works well.

How to Plant Dahlia Tubers

Planting dahlias is surprisingly simple.

1. Dig a hole 4–6 inches deep.

2. Place the tuber horizontally (as if you’re putting it to bed).

3. Cover it with soil.

   

If the soil is already moist, you usually do not need to water at planting time. In fact, I often recommend waiting until you see the first shoots emerge before watering to help prevent rot.

If your soil is very dry, a light watering at planting is fine.

How Far Apart Should Dahlias Be Planted?

For a typical garden bed, space dahlias 18–24 inches apart to allow good airflow between plants. Larger varieties will benefit from the full 24 inches of spacing. Dahlias also look especially beautiful when planted in groups of three or five of the same variety, which creates a bigger visual impact in the garden.

As a flower farmer growing for production, I often plant my dahlias closer together (12–18 inches apart) because I harvest them regularly and cut the plants back hard. If you’re planning a cutting garden, this spacing method can work well for you too.

Don’t Forget to Label Your Dahlias

I highly recommend placing a weather-proof label with each tuber or group of tubers when you plant.

This step is easy to skip, but you’ll be glad later if you take the extra minute to do it.

I use simple white plastic plant tags and a pencil. Surprisingly, a regular pencil works better than a Sharpie, which can fade or rub off over the course of the season. When (or if) you dig your tubers in the fall, those labels will make your life much easier — because dahlia plants killed by frost all look the same!

The Waiting Game

Once your tubers are planted, the hardest part begins: waiting.

This can be a stressful time, especially for gardeners who are new to dahlias.

It’s normal for dahlia tubers to take anywhere from 2 to 6 weeks to show visible sprouts above the soil surface, depending on soil temperature. Some varieties are naturally slower than others.

During this time, resist the urge to overwater.

Watch the Planting Process

Here’s a short video I created showing exactly how I plant my dahlia tubers.

Watch me Plant a Tuber

It really is pretty simple. The most important thing is just getting them in the ground.

Next week, I’ll be talking about the most common mistake new dahlia growers make — and how to avoid it.