Expert: Long Island Gardener - 8/16/2008

Question
My zip code is 12414. When and how do I winterize the dahlia tubers for next. Thanking you for the information,I await your response.

Answer
As you know, the Catskills region is going to be too cold to leave these plants in the ground past October.  Certainly it would be risky even if you were to mulch them carefully and provide superb drainage.  You are right to want to lift these.

Wait for the first light frost, then cut the stalks down leaving about 3 inches left above the ground.  Keep them in the ground another 10 days or so, and then use a pitchfork to gently loosen and then dig up the whole clump.

You can't be too careful about this, Fran.  You don't want to damage the tubers.  Be gentle.  Many people try to short-cut this task by yanking on the stem.  Don't make that mistake.  You'll only destroy the tubers and turn your Dahlias into compost candidates.

Lift the tubers, then use a garden hose to clean the clump.  Cut roots off with a scissors and let the clump dry.

At this point you can store your tuber (in which case you can jump down a few paragraphs) or try your hand at propagation.

Cut the tuber with sharp scissors or a knife.  Carefully divide clumps in half by splitting with pruning shears.  You'll find a handy illustration of this procedure at the swan Island Dahlias website:

www.dahlias.com/index.asp?PageAction=Custom&ID=2#13

Each tuber should have an eye -- like you find on a potato -- at the point where the crown is slightly enlarged.  You'll notice the eyes are located mainly nearest the stem.

Cook up a homemade disinfectant in your kitchen by mixing a cup of Bleach to 3 gallons of water.  Let the tubers soak for 15 minutes to 1/2 hour, then place them on some laid out newspapers and let them all dry.  Keep them out of the sun.

Some people overwinter their tubers in plastic bags with vermiculite.  I prefer to keep them in peat moss in the basement, in an open plastic container.  You should mist them every few weeks with a spray bottle filled with water.  Store them someplace dark and frost free. Temperatures should hover around 55 degrees all Winter.

This is a very tricky autumn.  For me, this would not be the first year I did not dig my Dahlias up due to procrastination.  Last year, our first hard freeze seemed to come out of nowhere and the ground was solid rock after that.  Yet, to my sheer amazement, half the Dahlias survived - thanks to good luck and excellent drainage.

Now, when you put these back in the ground next year, don't rush it.  You don't want to plant them in Soil that is too cold, or you'll rot them, and all your hard work will be out the window.  And you don't want to delay the planting too long, because once those tubers start to sprout, they start using up energy.  If it is not warm enough, pot them in temporary mix, and grow them very warm somewhere in your house.  They don't need to be watered -- just mist them one more time before you pot them, and wait for the sprout to show above the Soil line.

Remember too that not even the most experienced Dahlia grower always scores a perfect 10 in this exercise.  Expect to lose a few.  You'll improve with experience, but we learn from our mistakes.  Stick with it, and you'll get better.  There is no such thing as a green thumb.  Thanks for writing.

THE LONG ISLAND GARDENER