General Plant Care

Dahlias like to be planted in slightly acidic soil (6.3 to 6.8).  Well drained soil is a must, as dahlias can rot if the soil holds too much moisture.  Plant in a sunny spot, some light afternoon shade should be ok.  If it is a taller variety, staking is recommended at the time you plant your tuber.  Water deeply once a week - in very hot weather, watering more often would be required.  Fertilize with a  5-10-10 or 10-20-20 fertilizer as too much nitrogen will result in a big plant, with no flowers.  I used an organic seaweed fertilizer, that I mixed with water and sprayed on the dahlias for the 2015 season and it seemed to work great.

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Planting in Spring

In the PNW, our general rule is we are out of frost danger on Mother's Day.  You want to have your ground temperature at about 60 degrees and a couple weeks with minimal rain when you plant your tubers.  A late frost will damage your tubers, and wet, soggy ground will rot them before they have a chance to grow.  

Plant in a sunny area in good garden soil that drains well.  If you have clay soil, you will want to add amendments to the area that you are planning to plant your dahlias, or you will not have good results.  Our soil is fairly rocky (ugh) and drains well, I've found mushroom compost works best for me as an amendment for the soil and a natural fertilizer.  I add 2 to 3 inches of compost to the soil and work in.  You could also rototill.  

Dig about a 5 to 6 inch deep hole large enough to place your tuber into, add a tblsp. of bone meal and place your tuber in the hole.   Now is a good time to stake your tuber, so later in the season you don't damage it be adding a stake - honestly I've done it that way too and they have been fine.  Cover  & wait.  Waiting to see that first sprout come up is the hardest part!!  Usually in about 2 to 3 weeks your dahlia will sprout and start to grow.  (In our heat wave of 2015, some of my dahlias took 2 months to finally come up - I have no idea what they were doing down there!)

Care during growing Season

High nitrogen fertilizer will result in a big plant with no flowers. Stick to 5-10-10 or 10-20-20 or something else with a lower nitrogen number (that's the first one).  Last year I used an organic seaweed fertilizer, applied with a liquid sprayer every 3 weeks.  That seemed to work well.   If you use a granular fertilizer, fertilizing twice over the season will probably be enough.  As your plants grow, tie them to a stake to keep them from falling over or breaking from the wind.  Watch them bloom!!!  There are a few pests that like to munch on dahlias. Slugs will attack when the first sprouts come up in May - use Sluggo, crushed oyster shells, or anything else that you can find to keep them away.  Aphids, thrips and cucumber beetles will also try to eat your flower buds and blooms.  I try to use organic and non-toxic sprays to keep them at bay, as they will much on the petals and wreck their appearance.

Dig in Fall

Here in the PNW, we generally have our killing frost close to the end of October, depending on where you live.   After the first frost, cut back the stalks to about 6 to 12".  Wait one to two weeks, then dig, clean and store your tubers.  There are some great videos on YouTube that show you how to properly dig your tubers.  In general, using a shovel, loosen the soil starting about 12" away from the stalk.  You don't want to cut your tubers in half.  Dig up the whole clump, making sure not to break the "necks" of your tubers.  The neck is a very important area where the tuber attaches to the stalk.   This is where the "eyes" are and where next years plants will grow from.  If you happen to cut off the back end of your tuber - it will be just fine as long as 1/2 to 3/4 of the whole tuber is still in good shape and attached to a growing eye at the neck.

Storing during Winter

There are lots of ways to store tubers.  In different climates, you can also store them differently.  I am in the PNW and we have cold (usually between 20 to 35 degrees - occasionally we have a cold snap than can get us into the teens) and wet (resulting in fairly humid) winters. If you live in an area where your temps go negative - you certainly want to protect your dahlias from freezing.  A frozen tuber will not survive and will rot in your storage container.   

I wash the dirt off, soak in diluted bleach water for 20 minutes, let the tuber dry - usually this is overnight to a couple days depending on the weather.  Let them dry in a location that isn't too warm, but protected from freezing, like an unheated garage or outbuilding.  I dip the cut ends in sulfur dust and pack into plastic grocery bags using damp peat moss or dry cedar shavings as a storage medium, to both protect from freezing, and also to separate each variety from their storage mates.  If one tuber starts rotting, it can spread to the rest.  I don't tie up the bags, you don't want them to be air tight.  Then I put into a cardboard box or plastic tub to store for the winter.   If you use a plastic tub, make sure the lid does not make an air tight seal - condensation will rot your tubers.  Store in an unheated shop or garage that stays around 40 degrees.  Check on your tubers once a month to make sure none are rotting.

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Dahlia rows, July 2015

Bristol Karma

Those are some big tubers! Digging & washing, October 2015.

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