Avoid These Plants Near Dahlias for a Flourishing Summer Garden

Dahlias are stunning summer blooms that add color to gardens well into fall. While it might be tempting to plant them alongside various flowers and even vegetables, not all plants coexist harmoniously.

You don't need to be a gardening pro to cultivate dahlias, but understanding their requirements is essential for their success. According to a horticulturist, 'Dahlias are heavy feeders with specific needs regarding pests, airflow, and competition for roots. While some plants thrive together, others can obstruct dahlia growth or attract pests.'

Here are five types of plants you should keep away from your dahlias to ensure a spectacular bloom.

1. Plants with High Water Needs

Compatibility in water requirements is crucial when selecting companion plants. For example, some plants thrive in moist conditions, while dahlias prefer drier soil. Planting water-loving species next to dahlias can lead to maintenance issues.

A horticulturist emphasizes this by saying, 'Plants that love wet soil, like flag iris and marsh marigolds, are poor choices because dahlias will rot in overly damp conditions. Keep these species in rain gardens or wet spots.'

'Drought-resistant plants also don't pair well with dahlias, as they require well-draining, moist soil,' she adds.

2. Certain Vegetables

It's advisable to keep members of the cabbage family, like broccoli and kale, away from dahlias. These can lure aphids and caterpillars, which may spread to dahlias, damaging their leaves and flowers.

Though pest control is possible, it's best to keep these greens in a dedicated vegetable patch. Certain companion plants, like marigolds, can help deter pests from your crop.

Additionally, potatoes should also be kept at a distance from dahlias due to their shared susceptibility to diseases. 'Potatoes can harbor viruses that may infect dahlias, leading to serious health issues,' she warns.

Tomatoes, peppers, and eggplants should also be planted away from dahlias, as they attract spider mites, particularly in warmer areas. 'These pests can be very harmful to dahlias, so proximity increases the risk of an infestation.'

3. Large Perennials and Shrubs

Dahlias need ample sunlight to thrive, making areas with limited light unsuitable for their growth. When selecting companion plants, consider their mature height.

Large shrubs and trees, like hydrangeas, are not ideal. They may overshadow dahlias, stealing sunlight, water, and nutrients.

'Dahlias have shallow roots, so larger plants can easily outcompete them for resources. This also applies to tall perennials like Joe Pye weed and rudbeckia,' she states.

4. Zinnias

Although zinnias are great cut flowers, it's best not to plant them near dahlias. They are prone to powdery mildew, which can easily spread under humid conditions.

When zinnias are too close, they can inhibit airflow, worsening mildew problems for both plants. It's wiser to cultivate zinnias in a separate cutting garden where good airflow can help prevent mildew.

5. Sunflowers

Sunflowers are another popular annual that should be kept away from dahlias. They are tall plants that require significant nutrients, often competing with dahlias for water and minerals.

'Plant sunflowers in their own sunny area, ensuring enough space or additional feeding to minimize competition,' she advises. Alternatively, you may grow sunflowers in pots, such as the 'Tiger Eye Hybrid' from Burpee.

Maintaining Dahlia Health

What harms dahlia tubers?

Excess moisture and cold can lead to dahlia tuber rot. It's essential to select an appropriate planting site and properly overwinter them. Many gardeners dig them up in fall for safe storage until spring planting.

How should you space dahlias from other plants?

While some plants are suitable companions for dahlias, don't crowd them. They need room to grow and access nutrients. Spacing varies by variety, but generally, keep them at least 12 inches apart. Each variety typically has specific spacing instructions on the label.

Maintaining distance from incompatible plants helps your dahlias thrive, free from competition and disease. Thoughtful spacing encourages healthy, abundant blooms.

Explore our guides on pinching and deadheading dahlias for more tips.

This 'Lanesborough Pot Planter' from Charlton Home is perfect for showcasing your cherished perennials and shrubs - especially dahlias.

With a long, sharp blade, this hori hori knife is perfectly designed for weeding in the borders around your prized shrubs.

This 'Myrtlewood Planter' by Gracia Oaks is perfect for small to medium-sized shrubs and perennials, and would be great for dahlias, too.