Dahlias’ heat tolerance well suited for a changing garden

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Native to Mexico and Guatemala, dahlias were declared the national flower of Mexico in 1963 and have become one of our most iconic garden flowers.

David Jack is a third-generation dahlia grower with Ferncliff Gardens in Mission, so I asked for his insight on why they had gained such popularity. He said that few other flowers offer such a wide range of vibrant colours and colour patterns in so many flower forms and sizes. Not only do they make a great show in our gardens, but they also provide magnificent cut flowers.

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The current, and growing, appreciation for cut dahlias is certainly verified at United Flower Growers in Burnaby, the world’s second largest flower auction. Dahlia stems make up a significant portion of all the cuts sold at this time of year.

I was curious if certain flower forms make better cuts and Jack said varieties with flower heads from the 10-20 centimetre size are ideal for florists. He also mentioned that probably 75 per cent of all dahlias grown in the garden or on dahlia farms are used for bouquets. While commercial growers will often disbud small side shoots to encourage longer, sturdier stems, the home gardener can simply harvest the longest stems for a continuous supply of beautiful cut dahlias well into late summer and fall.

I mentioned that, traditionally, you put fresh cut flowers into quite warm water at first so they will drink quickly and last longer. He laughed and agreed, adding that floral preservatives also help, but that for many years they have just cut them, put them in water and enjoyed their beauty.

When asked if he had some favourites for cut stems, Jack named Ferncliff Ebony, their blackest red; Clearview Sarah, white with pink dusted petal tips; Ferncliff Rusty, a deep rusty orange, ball-bloom type; and Ferncliff Gumdrops, a bright yellow.

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Dahlias are very heat and drought tolerant so are ideal plants for hot summers like we are having this year, but there are still a few issues to watch for. He said thrips and aphids are two of the most common insect issues. We both joked about aphids being reasonably easy to control while thrips are extremely challenging — especially in home gardens — because there are so few pest control products left on the domestic market to deal with them. Picking off older, spent blossoms is also important for insect control.

Mildew is also a big problem this time of year and Jack mentioned the importance of watering in the morning and keeping foliage dry at night whenever possible. He recommended a thorough, deep watering when you can, keeping within current watering restrictions. He also suggested removing some of the bottom foliage to increase air circulation around the stems and leaves.

One of the better domestic pest control products is Safer’s 3 in 1 Garden Spray which helps keep aphids, mites, and fungal diseases in check.

He said feeding your dahlias at least weekly is critical. They are under a lot of stress this time of year, and to keep the plants healthy and producing flowers continuously, they need the extra nutrient. Something like Miracle Gro’s Bloom Booster 15-30-15 formula this time of year is  crucial, but by the end of September it’s important to stop feeding, as well as weaning them off the extra water to toughen them up for early frosts.

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Jack said one concern — for overwintering purposes — is that too many gardeners lift them up far too early. In the Lower Mainland the very end of October or into November is the ideal time to dig them up. His advice on digging is to first cut all the dahlia stems down to about 30cm above the ground. Second, dig a good-sized trench around the root ball so it can be easily lifted out with a fork.

The soil mass must be carefully cleaned away as much as possible, exposing just the tubers. At this point he does not recommend washing the tubers; its best to keep them dry. Lastly, lay them out separately in a cool, ventilated area to dry thoroughly — and he will often put a fan on them as well before wrapping them individually in newspaper. The newspaper breathes and helps protect the tubers. Store them in a cool room that can be kept above freezing, but under 15 C. In about mid or late April you’ll be ready to replant for another spectacular show.

Ferncliff Gardens has been one of our outstanding dahlia breeders and growers for three generations. Many of their own dahlia varieties can only be found on their website: ferncliffgardens.com

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This year’s crop is still growing and will be harvested this fall for sale next spring. You can place your orders online to ensure availability of some of their magnificent varieties.

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