Dahlias are gorgeous and come in many forms, from voluptuous dinner plate blossoms to perfect little poufs, not a petal out of place. But not in my yard. I’ve not succeeded in getting any to blossom, perhaps because they thrive with more water once they’re started than we distribute. Those we planted last spring were initially eaten by birds or vertebrates of some sort.
Robert Wallace, co-owner of Ramona’s Flower Farm in Caldwell, grows many dahlias. He said the tubers are very sensitive to moisture, so he plants his in spring 12 inches deep, and adds zero water until the foliage is at least an inch above soil level. Once they’ve grown to produce 5 or 6 leaves, he snips off the leader to encourage bushiness and flowers. Then he pulls soil up around the plants, hilling them to prevent their toppling.
Watch out for thrips and spider mites attacking them.
Dahlias are native to Mexico and central America, where plant explorers found dahlia tubers were used as food by Aztecs. Flower lovers took a second look at what tuber diggers were tossing aside as they dug, and started a new horticultural craze, adorning gardens, inspiring breeders and collectors, and leaving behind the “food crop” origins of this remarkable plant. They’re hardy only to USDA zone 8, not hardy in our area. Unless you planted tubers quite deeply, they’ll be killed by frost.
After frost blackens the foliage, wait at least four days, then dig the tubers. When frost kills the foliage, the tuber is stimulated to create eyes that will become new sprouts (for new plants). The window for digging tubers after a killing frost is four to eight days, before the ground is frozen. Tubers may have spread apart from the central stalk by as far as 12 inches, so begin digging your tubers carefully, about that far from the stem. Some folks use a spade, others a spading fork. If you damage tubers with your tools, later trim back the damage with a sharp knife.
Some folks keep tubers dry, others dip them in fungicide or a 10% solution of bleach and water, and then let them dry. Central stalks are hollow (thus other names for dahlias are water pipes and synonyms of those words), and large stalks may hold water. Store tubers with that stalk pointing downward for drainage while drying the tubers.
Tubers should be brushed free of soil and stored in containers of insulating material, from kitty litter to sawdust. I did use vermiculite for tuber storage a few years ago, and had no mold on stored tubers. Tubers should not touch one another, and the container should be stored in a cool area not subject to freezing.
ready new beds now
If you want to enlarge a flower or vegetable bed without too much labor involved, determine the borders you want, and start on it now. If it’s to replace lawn, mow closely before you start. You won’t have to remove the sod. If the area is in weeds, mowing helps, but if any of the weeds are perennial, they’ll cause problems later unless you first remove them.
If you want a curved border, use a hose or a rope to set the design, then lay out 10 plies of newspaper sheets or corrugated cardboard over the new area, overlapping newspaper or cardboard so there are no vacant spaces. Top that with lawn clippings (not containing traces of herbicide) or shredded spent plants or fallen leaves. Weigh this layer down with a topping of compost or soil, then after more leaves have fallen, add a layer of leaves, again weighing it down with soil or compost.
This “lasagna” of soil components should yield good friable soil to plant in by planting time next spring. If you’re in an area of the valley where caliche or lava is close to the surface, raised beds facilitate gardening, by providing more vertical soil for roots. Areas in southwest
Ada County have caliche and/or lava tubes lying shallow in soil, for instance. Beds wouldn’t have to be high, perhaps ten to 12 inches high would be adequate.
Some folks have even established raised beds for gardening over concrete.