Growing Dahlias for Colour Into Autumn
Between approximately August and the first serious frost, a majority of gardens feel tired. Initially, blooming perennials start to fade and new roses have not fully opened. Dahlias provide a solution for this gap in your garden. With proper growing conditions, dahlias will bloom while the majority of the other plants have completed blooming for the year.
Previously, we discussed tulips and while they are flowering cousins, dahlias and tulips have some fundamental differences. Tulips are true bulbs and should be planted in the autumn and largely forgotten until they bloom. Dahlias, on the other hand, emerge from tubers, which look like knobbly, brown, sausage links, and are a summer blooming flower. Because dahlias are summer blooming flowers, the shoots above ground are killed by the first frost of autumn and dahlias should be planted in the spring. If you are reading this in June, the tubers should be planted by now and should be sprouting. If not, get on it.
The jobs that matter now
By mid-summer, dahlias should be planted and the focus turns to maintaining productivity for the rest of the summer. There are two essential tasks that are often skipped, but improve growing conditions significantly.
The first is staking, which you probably should have done already. Dahlias tend to get top-heavy, and the large, flowering dahlias usually flop or snap from the first August rain without support. The lesson learned the hard way is to place the stake when the dahlia is being planted, before a tuber has formed to pierce. If you have forgotten, push in a stake, away from the plant’s center, and tie the dahlias, loosely and securely. A loose tie is best, as a tight tie will cut into the dahlias and be irreversible.
The second is pinching out. When dahlias have three or four pairs of leaves, the last growing point should be pinched out. The perception is that the last growing point is the active growing tip of the dahlia, which is why many find it wrong to cut the last growing point, but it forces branching and results in a bushier structure, helping dahlias carry more flowers and differentiate from a single-stemmed structure. More flowers make the dahlias more colorful.
Slugs will test your patience.
It is fair to warn others about this. Young dahlia shoots are like a buffet to slugs. A healthy tuber can be cropped to the ground by a slug overnight, only to leave you wondering in July why your dahlias have not progressed.
There is no perfectly right answer to this. Nightly patrolling with a torch can genuinely keep pests away if you’re bothered enough. Outside of that it’s more of the standard collection- gritty barriers, wool pellets, the rest. None are foolproof. Once the plant matures, pests get more disinterested as they woody out at the base so the key is really getting it through those first few weeks.
Feeding and the long haul to autumn
Once buds begin to appear, feed with a high-potash food like tomato feed every couple of weeks. What you’re trying to do is avoid nitrogen, which results in a plush, leafy plant with a sparse bloom. Bouyant growth with sulky flowers- the potash encourages bloom.
The rest of the season is spent deadheading, and this is typically where most people start to lose their patience. A spent flower and a budding flower can look very much the same. The main giveaway to the difference is the flower bud. A flower bud that is about to open is round and ball-like. The petals of a flower that has just finished blooming have dropped and tapered to a point. It is then continued deadheading that encourages bloom instead of seed set, while ceasing this will result in a cessation of bloom.
If they don’t stop eating, they’ll be carried until the end of it all. The best time is September through October as the light turns to a golden hue. They cut well to the house and don’t be careful about it, because they get thrown the more you cut.
It will eventually frost, typically in the middle of fall, and after the first hard one, the leaves blacken almost overnight. In the most of the country, you lift the bulbs, let them dry up, and store in a frost-free location until the spring. In other regions, the bulbs remain in the ground with a thick top layer of mulch and nothing else. I have lost some the ways I have done, but that is a job for another month. For now, you can enjoy a whole summer of growing.