FLIMBY: Plant dahlias now for late-summer flower power

This is another installment in our Flowers in My Back Yard series, focused on blooming plants.

Dahlias are definitely having their moment.

Darlings of social media and wedding designers, dahlias seem to be everywhere online. They currently rank among the most requested bridal flowers (especially for late summer or fall nuptials), but they’re beautiful for any event – or sunny garden.

Incredibly photogenic, this perennial flower comes in 14 different shapes in every color but blue (plus lots of combinations). Their size ranges from “pompoms” smaller than a cotton ball to “dinner plates” the size of serving platters up to 15 inches across.

Dahlias were made to be homegrown (or close by). Because they don’t ship well, this popular cut flower needs to be grown near its destination (such in a vase or bouquet), making it the poster posy for the farm-to-vase movement.

This also has prompted vegetable farmers to grow dahlias as a side crop, offering them at farmers markets or fruit stands.

Dahlias appreciate the same conditions as several summer vegetables, making them an ideal companion flower. If you can grow tomatoes, you can grow dahlias.

Fortunately for Sacramento-area gardeners, dahlias love it here. They thrive in hot summer sun and, if planted now in May or early June, they’ll bloom from late summer until frost.

I know from experience. My favorite red dahlia bloomed well into December, providing fat Christmas bouquets.

Dahlias grow from tubers. They look like grayish sweet potatoes (but don’t eat them). They multiply year after year, producing more and more plants. Like bearded irises, they benefit from periodic dividing and replanting.

In snowy climates, dahlias are “lifted” (dug up) and stored each winter. In Sacramento, tubers can stay in the ground – as long as they get good drainage. If planted in a low spot with clay soil, they can rot.

Drainage and sun are keys to dahlia success. They appreciate loose, loamy soil with a lot of organic material. Choose a location with 6 to 8 hours of sun a day.

Start with a 6- to 8-inch hole. Dig compost into the soil before planting. Add a tablespoonful of bone meal.

With their “eyes” (growth points) pointing up, plant dahlia tubers relatively shallow, covered by 2 to 3 inches of soil. (Smaller tubers need only an inch.) Unlike potatoes, don’t cut tubers up; they need to be planted whole.

Wait for the tuber to sprout before watering. Then, water regularly and deeply twice a week during summer. Put your dahlias on the same water diet as tomatoes, 5 gallons a week per plant.

As for fertilizer, be stingy. Feed dahlias half-strength balanced fertilizer (such as 8-8-8) once a month during their growth period. Too much nitrogen produces all leaves and no flowers.

Dahlia tubers need to feel warmth, so don’t mulch. Leave the ground bare around the plant. (Mulch also can harbor snails and slugs, the main dahlia pests.)

The hardest part of growing dahlias? Choosing which ones to to grow. More than 20,000 named varieties are available. And some can get very pricey; a single tuber for the most popular varieties (such as beige-pink ‘Cafe au Lait,’ a favorite of wedding designers) can cost $20, $30 or more.

When picking out varieties (and where to plant them), remember: Dahlias can get really big. While some border or bedding varieties stay compact (and knee high), most dahlias will grow 3 to 4 feet tall – or more. (Larger dinner-plate varieties often top 6 feet tall.) If planted next to vegetables, they will shade their neighbors in late summer. (Bell peppers, for example, could use that shade.)

Dahlias need room, too. Plant the larger varieties at least 2 to 3 feet apart.

Or plant them 1 foot apart and create a dahlia “hedge”; their tall stems will support each other.

Support is key to big long-stemmed dahlias. As they grow rapidly, those heavy flower heads can topple the plant. Stake the stems as they grow, tying them with soft string or yarn. That extra support will keep the plants looking tidy as well as protect them from wind.

After sprouting, dahlias take 8 to 12 weeks to bloom. If they're planted now, you can expect to enjoy bouquets in August – and throughout the fall.

The more you cut dahlia flowers, the more they’ll bloom. Regular deadheading prolongs their season by months.