The cultivation of dahlias brings to mind the famed Longfellow little girl verse. “When she was good/She was very very good/But when she was bad she was horrid”. Even if you give them everything you’ve got in the way of rich soil, good sun, staking, fertilization, good air circulation and your utmost devotion, it may not be enough. You still need the blessing of the patron saint of all sulky, troublesome prima donna garden flowers-whomever she may be. Not that one could ask for that blessing; it must be bestowed. I do have one client for whom they perform on demand. He says its the soil-I say what he manages with them is magic.
There are lots of reasons not to grow them. Their stems are weak and floppy, and snap off without any provocation; a wind is likely to send them, along with the building of stakes you have erected around them, crashing to the ground. Bugs love them even more than you do. Earwigs set up housekeeping deep in the petals. They can become infested with, and succumb to spider mites in what seems like the blink of an eye. The plants are as awkward and ungainly as a teen-aged tea rose. Some shorter more stocky varieties are shy bloomers-figures. They hate cold weather, and cold weather goes with our gardening territory.
Some sport blooms so large the word vulgar comes to mind. Some “dinnerplate dahlias” have stems so weak the plant perpetually looks like someone spent the last hour giving them a thorough dressing down. Fungus spreads like crazy from the bottom up; I have grown plenty of dahlia stalks with a few anemic and forlorn flowers on top. When I grow them in pots, I face them down with something that has the decency to grow vigorously, and hide those ungainly dahlia legs.
So why do I grow them? In a good year, they are magnificent. Loaded with flowers, they remind me of the 19th century flower paintings of Rachel Ruysch; they are supremely grand. The range of colors and forms is astonishing. This dahlia is a “formal decorative” type. Park Princess has petals shaped like quills; this form is known as a “cactus dahlia”.
If you have a love of color, dahlias deliver. From pure white to the most audacious orange to carmine, all of the warm colors are represented. The bicolor varieties evolve in appearance over the summer. When temperatures start to cool off in the fall, the contrast in colors seems to intensify. No doubt they are the big brass band of the flower world.
I am looking at these dahlias now as they have been at their peak this first week of October. There is something to recommend about how they last into the fall. They do hate cold weather; the best grown dahlias are those that have spent May and June in a greenhouse. They transition from that museum like setting to the Michigan outdoors poorly. It can take weeks before they loose that insulted look, and take hold.
I think a too early planting can set them back such that they never recover. They thrive in that rarefied hothouse atmosphere where wind, bugs, cold soil, and various pathogens are simply not permitted. Dahlias are not great garden plants; they are an event you may wish to attend.
Some of these party girls dress in a way that’s just plain fun to look at. When they are at their overblown best, they make me smile.
Now is the perfect time to decide if and which you will grow next year. They have put on the most glorious show this season I have ever seen, and I would not mind being treated to that again sometime soon.
My idea of sheetcake has nothing to do with cooking batter in a pan. It has everything to do with the idea of planting shrubs in masses. There are those times and places where planting out in rows has its place. Field rows of corn, asparagus, peonies or cutting flowers can be an astonishing sight. Many years ago I designed just such a garden for a client who tithed the use of the land surrounding his house to his church. This, the intersection of agriculture and landscape. Some years later I dicovered the work of the Spanish landscape architect, Fernando Caruncho. His gardens explore the idea of agrarian based landscape design on a grand scale. His landscape, Mas De Les Voltes, I admire as much as any landscape I have ever seen. But my intent with the above pictured landscape was to suggest that a drivecourt had been carved out of a mass of taxus. Though most of the mass is actually drivecourt, the suggestion of great mass remains. Shrubs planted formally en mass-I call this a sheetcake.
Very small urban properties can be sheetcaked to good success. One has to choose as few gestures from many possibilities, given a small space. Too much going on in a small space dilutes the impact of the landscape. In this case saying less truly is more.
A very flat piece of land achieves a change of level with the interaction of two plant materials of different heights. 
The dusting of fall leaves provides another dimension as the limelights are fading.
A sheetcake garden is an effective way to showcase abrupt changes in grade. I am all for celebrating any unusual characteristic of the land. One client had a low lying front yard, and an active artesian spring. I dug the ground deeper, and created a pond. The sidewalk to the front door was actually a boardwalk over the pond; you get the idea. The artesian spring was treated as an asset, rather than a nuisance. Accommodating nature helps produce a successful project.
A tree inset into a sheetcake provides another layer of interest. I have talked about the spent magnolia petals on these boxwood in the spring-it is a sight for my gardening eyes. 
