When placed in a vase with other flowers, dahlias make for a beautiful accompaniment, with striking colors that partner well with almost any arrangement. Place these tuberous plants in your vegetable garden, however, and they’ll be a bit less neighborly. Three of the worst dahlia bedfellows come from the brassica family: broccoli, cauliflower, and cabbage.
The first issue between these plants arises the moment they touch soil. All four require acidic soil, usually between 6 and 7 on the pH scale, so if you plant them together, they’ll be constantly fighting for nutrients. You could solve this problem, to an extent, with proper spacing between the plants but then comes the next hurdle: pests. Dahlias come with a lot of insect problems, with aphids being particularly fond of the flower. And these annoying bugs just happen to enjoy nibbling on those three brassica vegetables, too. Pairing them all together essentially creates an aphid-friendly buffet.
Broccoli, cauliflower, and cabbage share diseases with the flower as well. This includes powdery mildew and a fungus that causes wilting. When grown in close proximity, brassicas and dahlias will pass these diseases from one to another.
Favorable flower matches for brassicas
While dahlia may be out of consideration, growing flowers next to members of the brassica family isn’t an unattainable dream. There are actually a number of blooms that can bring beauty and benefit to your vegetable row, with nasturtium serving as one of the top options. This flower usually grows shorter than our three brassica vegetables, and that extra ground cover lowers the soil temperature and helps with water retention during the hot summer months.
Nasturtium also serves as a great pest deterrent, as does yarrow. This flowering plant attracts a number of beneficial insects, including those that attack brassica-loving pests. Cabbage moths can be particularly harmful, not only to its namesake plant but to broccoli and cauliflower, too. Those moths, however, have an enemy in certain wasp species. Coincidentally, it’s the same wasps that are attracted to the alluring scent of yarrow. Plant the flower near your crop, and you’ll be gifted with a natural defense.
Stick with herbs, not vegetables, for dahlias
While broccoli, cauliflower, and cabbage are particularly unmatched against the dahlia plant, it’s best to avoid vegetables altogether when planting near the bloom. The risk of pests and disease is just too high to justify any visual benefit that can be gained from the pairing. Instead, try growing herbs next to the flower.
There are a number of herbs that make for a good companion to dahlias, namely because of their ability to repel troublesome insects and attract beneficial ones. That list includes rosemary, thyme, coriander, mint, anise, and cilantro. Lavender can provide that same benefit while adding a beautiful pop of color, too.
If you want to match your vegetable garden to the dahlia area of your yard, nasturtium will do the trick. The plant is versatile in its pest defenses, keeping annoyances away from broccoli, cauliflower, and cabbage, while serving as a trap crop for dahlias. Aphids, specifically, will go for the nasturtium, leaving the delicate dahlia alone.
