My love for dahlias got off to a really slow start. I much preferred soil beneath my fingernails than for those same nails to be blackened by bruises from driving dahlia stakes into the ground. And the truth was, dahlias had no other purpose on earth than to stand around looking totally tall and beautiful. I liked plants that had a reason for being, like tomatoes. Now there was a plant worth growing even if it did need to be staked.
Aunt Bett always said, "Unless a plant gives us food or medicine, ain't no reason for 'em to take up garden space." I thought everything Aunt Bett said was always true but my mother had other ideas. She said her plants and her gardens were just for beauty and that beauty was important too. I reckon it was a bit of a dilemma for me at the time because her gardens were truly beautiful and eventually her huge colorful dahlias became backdrops for all of them. That was because Mom took very good care of her dahlias. From storing them in Autumn to planting in Spring and growing them all Summer long, never a day went by that Mom didn't check on her dahlias; never a year went by that her dahlias weren't magnificent. Through the years I learned the secrets to her success; I'll even share them with you.
First, about planting:
*Don't be in a hurry to plant, dahlias have a difficult time in cold or wet soil. Wait till the ground temperature is above 60F, when you're sure there's no longer any danger of frost or freeze.
*Be sure you plant in full sun and if they are in morning sunlight, that's even better. Wind is never kind to them, so check to see that your sunny spot isn't too windy.
*The planting holes can be anywhere from 6" to 8" deep, my suggestion is to dig a little deeper in cold climates just in case you miscalculated the last frost. Those few extra inches will protect the tubers and keep them warmer.
*For tall dahlias, before you even put the tubers in the soil, pound your stake into the ground beside the hole. This prevents any stake damage to the tuber.
*Small bushy dahlias need to be planted about a foot apart. If they will grow to 3 feet, then plant them a couple of feet apart and if they are going to be over your head, they might need to be 3 feet apart. It's guesswork, but after your first bloom season, you'll know for sure what they need.
*The planting hole must be a bit larger than the root ball. Add a little sphagnum or compost to the hole, but don't fertilize at planting time.
*Check to make sure you don't plant wrinkled or rotting tubers, they're already beyond help. A little bit of green growth on the tuber is a good thing.
*Don't break or cut apart the tubers. These are not potatoes and they for sure don't grow like potatoes so plant the entire tuber with the growing points facing upward.
*Plant with the crowns slightly above the soil line.
*Don't water tubers just after planting; as long as the soil is damp, they'll be just fine without more water. Watering at planting time will just encourage rot, so wait till you see a bit of new growth emerging, then water. This is simply a safety measure and another bit of guess work, but since tuber rot is a real enemy, it pays to be cautious.
*Don't cover the tubers with bark or heavy mulch because it's too challenging to new growth. The growth will have to work its way around chunks to reach the surface and winding around will simply weaken the bloom stalk that's trying to grow. It needs to be able to shoot straight for the sky and stand there when those heavy blooms begin appearing.
*Do apply slug or snail bait when planted, if those little critters love your gardens. The bait will help avoid them.
Now you have dahlias growing, what's next?
*After your dahlias are established, deep water about every 2 or 3 weeks, using a gentle spray because baby dahlias are quite fragile.
*Low nitrogen fertilizer is good, the kind you use in a veggie garden. Adding a little fertilizer after sprouting and then again about once a month is great, dahlias love it. Just be sure you don't over fertilize.
*After heavy rain, dahlia blooms might need a little shake to get rid of the water their petals are holding. If it's windy, check to make sure the stakes are holding them up.
*Short varieties need to be pinched at the growing point to encourage bushing and all varieties need to be dead headed.
*Tall dahlias need to be deadheaded but they don't need much pinching. Bushing makes them top heavy and inclined to lean or to break.
Just so you know, dahlias are hardy to Zone 8 and in Fall they can be cut back to about 4 or 5 inches and left in the ground during winter. Zone 7 is where we draw the line because we never know what kind of winter we'll get, neither do the long range forecasters. Sometimes mine are fine left in ground and produce gorgeous blooms the next summer with no problem. Sometimes they disappear, never to be seen again, so I'll leave that decision up to you. Whether to lift or whether to leave in ground, that's your question in Zone 7.
If you want to save your dahlia tubers in colder zones, then you need to lift them from the ground, clean them free of soil and let them dry for a day or two. They can be stored (with a little sphagnum moss between them) in a dry burlap bag or even in a basket. They also need to be placed in a dry area where they won't freeze. I usually keep mine in the same cool room with the bulbs that I save, caladiums, gloriosas and often those tubers for my sweet potato vines.
So beautiful, aren't they? I couldn't resist cramming this article full of photos. In spite of Aunt Bett's aversion to plants that offer nothing more than beauty, I realize now that unlike her, I love dahlias. What's not to love?
*They happily bloom late in the hottest part of the year when nothing else is blooming.
*The color is reliable, a dahlia will never revert to something it used to be.
*They are recyclable; if we care for them, we can plant those same tubers over and over again.
*They are perfect cut flowers for any late Summer occasion.
*They perform well in most any well draining soil.
*Deadheading provides more blooms.
Too much water is their enemy but we can control that with good drainage. We might have to control deer too, but otherwise, dahlias are easy plants. The short bushy varieties are great community plants, they could be grown easily in or around a vegetable garden, their needs are about the same as those of the veggies. The taller varieties are my favorites because they form a backdrop to my daylilies on my back hill. And when the daylilies are finished blooming, I can always count on the dahlias to provide more color.
With profound apologies to Aunt Bett and her medicinal/food plants, when it came to dahlias, I listened and learned from Mom. I think Aunt Bett would understand.