2011-10-13 / Editorial

The Island Garden

Grow dahlias for colorful blooms

I grow dahlias, rather a lot of them unfortunately. I say unfortunately because it is a lot of work to prepare the bed and to plant the tubers. But at this time of year the blooms are so prolific that I end up giving a lot of flowers away.

Dahlias first came from Mexico and according to many sources, all of today’s dahlias are derived from three Mexican species. With the exception of a few bronze-leafed varieties, all dahlias have deep green leaves. Because they came from Mexico, dahlias like warm temperatures and are easily susceptible to frost. By digging your dahlia tubers each fall, you can store them in a frost-free area and replant them next year.

The majority of dahlias we see today are grown from cuttings or by tuber division, however, some dahlias – known as bedding dahlias – can be grown from seed. These dahlias tend to be smaller and not as hardy as the larger border dahlias, plus they usually do not come true to seed.

Border dahlias are relatively easy to grow. To grow them you will need to obtain tubers. These days many outlets sell two or three tubers in a single packet. Before planting you should enrich the ground by digging in well-rotted manure or compost about two to three weeks before you intend to plant the tubers.

In spring all you need to do is put a tuber in the ground and wait for it to grow. It needs to be planted about 4 inches deep and spaced about 2 to 3 feet apart. As soon as the shoots get 3 to 4 inches high, they get eaten by rabbits, deer and any stray groundhogs that happen by. As soon as you see signs that the shoots are being eaten, it’s time to spray with Liquid Fence or Deer Off. Spraying does nothing for the flower smell, but it keeps the animals away long enough for the shoots to grow more than a foot tall. Once they exceed a foot or so, they don’t generally get eaten.

When they start to grow you will need to stake the plants or they will fall over and get eaten by slugs and snails. It can be quite tedious to stake a lot of dahlias and I’ve found the best way is to use gardener’s twist tie wire. Put a single loop around the stake and make a loose loop around the dahlia stem. Unfortunately, this year Irene came ashore just before I staked the plants so I have a lot of horizontal stems that had to be raised very gently.

In fall, right about now, or just after frost, you need to dig the tubers. If you dig them now, you will be able to label the tubers so that you know which colors will come up next year where you want them. If you leave them until frost hits, the leaves turn black and it is hard to tell what color the flowers were. Next season this leads to planting large patches of similar colored flowers.

When you have dug and labeled all your tubers, snip off the small shoots at the end and wash the dirt off them. Let the tubers dry out and box them for next spring. If you have the space in a greenhouse or cold frame you can start your tubers early and transplant them later.

When you take the tubers out of your storage bin, you should look for an eye on each tuber and cut the tuber from the main clump. You can plant each tuber in a pot and transplant it later. With a large enough greenhouse you can end up with a hundred or more tubers, all of which will end the growing season as a clump of tubers.

If you don’t want to start your tubers early, simply divide them individually – or clumps of two or three – and plant them. I put stakes where I plant them to help locate the tubers after the animals have eaten the tops. I find it is best to put a mulch of some type over the dahlia bed. This keeps the weeds under control while the plantlets are growing.

If you start your outdoor dahlias in early May, you should start to see flowers around the Fourth of July. Each week you delay your planting will mean your flowers will come up a week later. The flowers will continue until frost.

So, what dahlias should you grow?

Giant dahlias can grow to 4 or 5 feet high and give you flowers the size of a dinner plate. Plant them 4 to 5 feet apart in well-fertilized mounds. You will need to stake them or they will blow over easily.

Large dahlias also grow to 4 or 5 feet but their flowers are only 6 to 8 inches in diameter. You should plant them about 4 feet apart.

Medium dahlias grow 3 to 4 feet high and have blooms up to 6 inches in diameter.

You can also get small dahlias that have several 3- to 4-inch flowers on a stem or miniature dahlias that have smaller flowers.

Irrespective of size, there are single flowered, anemone-flowered, collerette, decorative, cactus and semi-cactus flowered, pom-poms and ball dahlias. As their name implies, pom-pom and ball dahlias form tight ball-like flowers. Cactus and semi-cactus flowered dahlias tend to have large spiky flowers, while collerette flowered dahlias have a single ring of petals rather like a daisy. Peony flowered dahlias have two rings of petals, while decorative dahlias have double flowers in what often looks like a large ball of heavily-petaled flowers.

With care you can get years of dahlias from a few tubers. As they expand you will have plenty tubers to spread around to your friends and in the meantime you will be able to enjoy a summer bed of brilliant flowers.

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