Growing Dahlias

I think of dahlias as plants that can suit any personality. Are you a person who likes to make a splash whenever you walk into a room? You might find that a fire engine red dinner plate dahlia is just the thing for your dramatic garden. Are you more circumspect, detail-oriented, like all your ducks in a row? A formal decorative variety in a medium-toned coral color would tick all those boxes. Perhaps you are on the shy side, happy to take more of a backseat than drive the car, but you never miss the beauty in the smallest of things. Take a look at a creamy white, tiny pompom dahlia and you might find your flower soul mate. There is no doubt that the abundance of shapes, sizes and colors of this beautiful plant offers choices to every flavor of gardener and garden alike. When you consider that the genus dahlia is a perennial in zone 9b, has a long growing season from summer through fall, makes a lovely cut flower, and is easy to grow, there's no reason not to add a dahlia to your garden.

Given the complexity and diversity of dahlia varieties, it's surprising to know that this plant had much humbler beginnings. Originating from Mexico and Guatemala, dahlias were grown for the tuber's food value and were initially much simpler in appearance, more like a daisy. However, with Spanish colonization and subsequent botanical exploration, seeds were brought back to Europe where horticulturalists hybridized the plant over the centuries, resulting in the diversity of blooms we know today. The size of blooms ranges from pompom (up to two inches) to giant (ten inches or more) with half a dozen sizes in between. The petals, or ray florets, can be wild and wavy, spiky and tubular, fringe-like, tightly packed and circular, open and flat, double or single. And the array of colors is spectacular: from bright pops of color to deep saturation, or soft pastels, and sometimes multi-colored.

So how do we grow these stunning plants in our own gardens? The requirements are less complex than the outcome. Dahlias grow from a tuberous root and that is most often how a gardener will purchase the plant, although they can be grown from seed or cuttings. The tuber, where all the plant's food storage resides, has a neck and eyes from which the plant sprouts. Depending on where you buy your dahlia tubers, they will come in either a clump of tubers connected by one neck, or one single tuber. A clump will sometimes have tubers that are broken at the neck or there might be a soft one that is beginning to rot. Simply remove these. All you need is one tuber, big or small, and as long as it has an eye, it will grow.

Planting time for dahlias is after the threat of the last frost. For Yolo County zone 9b, that typically means sometime in March. Dahlia's warm climate origins mean they won't thrive in cold environments, so the soil must be at least sixty degrees Fahrenheit at time of planting. Choose a location in your garden that gets at least six hours of sun a day to prevent the plant from becoming leggy. However, dahlias don't like extreme heat, so avoid overly-hot locations or be prepared to use shade cloth on exceedingly hot days. A spot in your garden that receives the majority of the day's sun in the morning is ideal.

Depending on whether you are planting one tuber or a hefty clump, you will want to dig a hole four to six inches or more. Your tubers will only need a couple inches of soil to cover them, so adjust the depth accordingly. Work some organic compost into the hole and then place your tubers. If you have a single tuber, lay it horizontally on the soil with the growth eye facing up. If you are planting a clump of tubers connected by a neck, place the clump on the soil with the neck facing up. For tall varieties which will need support as they grow, place the support stake while you can still see what you're doing. Locate the stake a couple inches from the neck, then cover the tuber with two to three inches of soil. For tuber clumps, make sure you fill in the soil around the tubers so there is no empty space between them. Space dahlias one to two feet apart for smaller varieties and four to five feet apart for larger varieties. If you are planting your dahlias in a container, choose a generous size, two feet or more in diameter and at least one foot deep to give your plant plenty of room to grow.

After the initial planting, lightly water the tubers, but then let them be until you see them sprouting. Dahlia tubers are very susceptible to rot at this stage, and they won't need water again until the plant breaks ground. Once the plant begins to grow, water routines will vary depending on your location and soil type, but keep in mind that dahlias do not like wet feet. Water deeply once or twice a week and more often in extreme heat or if your dahlia is in a container.

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nce your dahlias begin to sprout, they will be vulnerable to snails and slugs which can eat those sprouts right to the ground. Take preventative measures and just before you expect to see sprouting, in about four to six weeks, apply an organic bait around the planting area and reapply every week and after rain. Established plants should be able to withstand this pest pressure but continue applying bait if the problem persists.

When the plant has formed three sets of leaves, pinch the center growth just above the third set. This will give you a stronger, bushier plant with more blooms. Once your plant begins blooming, it will benefit from cutting, so don't be afraid to fill your vases with flowers; you will encourage the plant to bloom even more. The same is true of deadheading. Don't let spent blooms linger. Cut them off and allow the plant to put its energy into more flower production.

There are a variety of opinions on applying fertilizer to dahlias, and much of it depends on the health of your soil. If your soil is nutrient rich and you've applied compost at planting, that might be all you need, but if your soil needs some extra help use a low nitrogen fertilizer when the buds first appear. High nitrogen will encourage leafier growth over flower production, so choosing a fertilizer with a higher phosphorous level (the middle number on the fertilizer package, for example 5-10-5) will encourage the plant to produce more blooms.

Dahlias will bloom from mid-summer through the fall and will die back when temperatures drop. Allow the leaves to yellow and then cut the plant back to about four inches. Because of our mild winters, we can leave the tubers to overwinter in the ground. Another perk of growing dahlias is that the tubers will multiply each season. Every two to three years, you can dig up your tubers and divide them to plant elsewhere or give away and spread the joy.

So plant a dahlia this month. With so many forms and colors to choose from, your only challenge will be deciding which one. (Research is still pending on whether or not anyone has ever bought just one dahlia.)

For more details about dahlias, visit the American Dahlia Society. They also have information on local dahlia societies you can join, as well as upcoming dahlia shows. To experience the spectacular diversity of dahlias up close and personal, don't miss the dahlia garden at the Mendocino Coast Botanical Gardens. The flowers are in bloom from June through October, and it's a trip worth making.