Gardening Tips: Dahlias – A Highlight of Autumn

by Emma Herd
Why I love Dahlias, their origins and tips on how to grow your own.

History

Today beautiful Dahlias are so varied, with thousands of cultivars and hybrids available and approximately 41 known species. The single-petaled Dahlia, of the Asteraceae family is born of tubers. Their amazing blooms are native to South America and first gained popularity in the gardens of Mesoamerican Aztecs, in the mountain ranges of Mexico, Guatemala and Columbia, bursting onto the European horticultural scene in 1789.

A bit of Etymology – the original Nahuatl name, acocoxochitl, comes from the words a-ti (water), coco-tli (tube) and xochitl (flower), meaning in its entirety ‘flower of hollow stems with water’.

The plants gained their Latin name from Abbe Cavanille a prolific Spanish taxonomic botanist of the 18th century, in honour of Andreas Dahl a Swedish scientist and environmentalist. By the 1840s American horticultural journalists, were praising many new varieties every year.

Where’s the best spot to plant dahlias in your garden?

Dahlias like to have morning sun because it’s more gentle, and afternoon shade otherwise they’ll often wilt in the heat.

If your space is full sun, consider building a shade house. This will give the flowers the light conditions they need to thrive. If you’d prefer not to use plastic shade cloth, I’d recommend using hessian. Yes it doesn’t last as long as plastic but that’s a real advantage for the planet. Because it is made entirely from natural vegetable fibres, it is completely biodegradable. If you don’t have a budget for a shade house try visiting a coffee roaster. They’ll often have hessian bags that they’re discarding. Why not recycle them into your shade house.

A yellow Dahlia flower
A mauve and white Dahlia flower

Soil prep

Dahlias grow in most soil types, however, to thrive I have the following recommendations.

If you have a vegetable garden and like to rotate your beds, I recommend planting dahlias where you had any legumes the year prior. Simply dig in any languishing plants rather than pulling them out at the end of their season.

While you’re at it, thoroughly mix in some well-aged cow manure during the winter prior to planting your tubers. Poultry and swine manure isn’t recommended because it can damage developing root systems.

Another great advantage of dahlias near your vegetables is that they make great pollinator-attracting companion plants.

Back to soil – I have an irrigation system set up to water my plants every second day during summer. On top of this drip line irrigation, once my dahlias begin to grow their foliage, I like to top dress the soil with pea straw, sugar cane or lucerne. This of course can be beneficial to retain moisture in the soil.

One important caveat regarding this, is try not to place mulch right up against stems. If you do there’s increased potential for a lack of air flow, creating humidity at the base of the plant. This can lead to powdery mildew, especially early in your season. This can ruin plants before they flower.

When your plants begin to brown they can then be cut down to 30cm high. I live in a cold part of the state so mine get pruned back in March to April. Then I leave the tuber clumps in the ground until June, lift them, trim off the roots, and store each variety labelled individually.

A pink dahlia flower

When to plant

The best time of year to plant your dahlia tubers in Australia is the first week of November. This advice does vary depending on your local environment. It’s important to plant when the soil temperature is on the rise and any possibility of frost is over.

How to plant, lift and store

It’s always best to pop your stakes or support hoops in the ground first, so as not to pierce your tubers by accident later. Plant your tubers horizontally, in a hole about 10cm deep with the eye higher than the tail. You can of course plant in pots, if you don’t have the ground space. At the end of the season it’s best to raise and store your tubers over winter, to avoid them rotting, especially if you live in a place where temperatures drop enough for frost or snow.

When your plants begin to brown they can then be cut down to 30cm high. I live in a cold part of the state so mine get pruned back in March to April. Then I leave the tuber clumps in the ground until June, lift them, trim off the roots, and store each variety labelled individually.

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