Dahlia Planting Instructions
Dahlia plants are amazing, another excellent example of horticultural magic. The dinner plate types can grow a full four to six feet tall in just a few months while producing blooms almost a foot across. Underground, the same super charged thing is happening. Should you decide to dig up your dahlia tubers at the end of the season, you'll be impressed with what's been happening under the soil surface. Expect to find clumps of potato-like tubers which often can be divided into several pieces (and new plants) for next year's garden.
Find a location where the soil drains well. If there are still water puddles 5-6 hours after a hard rain, scout out another site. Or amend the soil with the addition of organic material to raise the level 2"-3" to improve the drainage. Peat moss, compost, ground bark or decomposed manure all work well and are widely available. Dahlias won't thrive in areas that are soggy and prefer soil that is rich enough to support their "heavy feeding" needs. Site your plants where they will receive full sun for the strongest stems and greatest flower production. Check the mature size and spacing information provided with each plant variety and design your placement accordingly. Dig holes. Examine your dahlia tubers and look for the point where the thick roots junction with the stem and check for little "eyes" or growing points bumping out. These are the spots where the new shoots will start. Plant these 3-4” deep, pointing upwards. Space your tubers 12-20” apart depending on the variety's mature size. The tubers will vary in shape, with some being quite round and others shaped like long ovals. Try to get the eyes facing up and don't worry if you get it wrong. Odds are very good that the plant will grow just fine anyway. Tuck the plants in and tamp down the soil to remove any air pockets.
After planting, water your dahlias generously to settle the soil around the tubers. Root and top growth form in a few weeks, depending on soil and air temperature. Water periodically during the growing season, as needed, keeping in mind that weekly deep waterings are better than lighter drinks every day or two. An estimate of 1" of moisture per week is a good place to start. If the dahlias you've chosen grow tall and/or have large blooms it's a good idea to provide a sturdy support stake. Placing the stake at the same time as planting helps ensure that you don't drive the stake through the tuber (because you've forgotten exactly where the tuber lies) and gets the job done before the plant grows quite large. When your dahlias bloom feel free to snip blossoms for bouquets. This will not hurt the plants, dahlia flowers are exceptional for arrangements and for some varieties snipping blossoms prolongs the blooming period. After blooming has finished for the year, leave the foliage in place, don't cut it off. The leaves gather sunlight, create food through photosynthesis and strengthen the plant for the future. In late fall, your plants' foliage will fade and wilt with the onset of colder nights. If you live in an area where the soil freezes and you wish to save your tubers for next year, pull up the plants after the first frost. Rinse off the soil, cut the stems to 3" and let the tubers dry for 2-3 days. Then tuck into paper bags or cartons with peat moss and place in a cool dry spot. Check the tubers monthly and sprinkle a little water into the peat if the tubers are drying up.