The Biggest Mistake You're Making With Your Dahlias—and How to Fix It

Dahlias are one of the most popular flowering bulbs. Their dramatic blooms come in all kinds of shades and sizes, and they last from summer through fall in most regions.

However, unless you’re an experienced gardener, it can be very easy to make mistakes when growing this finicky flower. Here, we share the biggest errors people make in terms of dahlia care, according to farmers and flower experts.

The Biggest Mistake: Planting Too Early

The biggest mistake people make is not knowing when to plant dahlias.

“This happens because gardeners don’t take the time to learn about the plant’s specific needs, especially when it comes to temperature," says Nastya Vasylchyshyna, resident botany expert at Plantum.

For example, some gardeners may rush to get their dahlias in the ground without waiting for the soil to warm up. However, skipping this step often leads to problems. “Dahlias should only be planted once the risk of frost has completely passed," she adds.

Even once temperatures stay consistently warm, it's a good idea to wait another one to two weeks, just to be safe. “Soil temperatures should be at least 60 degrees Fahrenheit, with the ideal range being between 60 and 70 degrees Fahrenheit,” says Dee Dee DeBartlo, master gardener and landscape designer at Green Farms Botanical.

Planting at the Wrong Depth

Planting tubers the wrong way is another common mistake.

“To grow strong roots and healthy stems, dahlias need to be planted at the right depth and in the correct position,” says Vasylchyshyna. Simply place each tuber horizontally in a hole about 5 to 6 inches deep, with the small growth bud facing upward. This position gives the plant the best chance to develop properly.

“Be careful not to damage the growth bud or the neck of the tuber (the thin part where the stem will grow from), as both are important for growth,” she adds. Planting the tubers too deep will cause the shoots to use too much energy to reach the surface, making the plant weaker.

Choosing the Wrong Spot

“Sun-loving dahlias need at least six hours of direct sunlight per day to thrive and bloom well," says DeBartlo. So don’t plant them in shaded areas.

You also never want to plant them in an area that has clay soil without first improving the drainage. However, you can amend the soil with compost, leaf mold, sand, perlite, or other organic material. If you don't, then the wet, compacted soil can cause your tubers to rot.

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Over or Underwatering

Watering too much or too little can be a major problem. Some gardeners overwater, hoping to speed up growth and get blooms sooner, says Vasylchyshyna. Others plant the tubers and then forget about them, leaving them to survive on natural rainfall alone.

“Overwatering is especially dangerous because it can lead to rot, damage the roots, or even kill the entire tuber,” she says. On the other hand, letting the soil dry out too much can prevent blooming.

Instead, DeBartlo suggests holding off on watering until you see visible sprouts. “Too much moisture early on can lead to rot before the plant gets established," she adds.

After the dahlias start growing, you can regularly water them. However, keep in mind that dahlias grown in containers usually need to be watered more often than those planted in the open ground.