They're in pots, outside, and the soil is still very damp.

This is my first year growing so I am no an expert but when I planted mine, in pots as well, I gave them a good watering too. It was hard to resist the urge to keep watering but I just let them go and let the soil dry up a bit and waited until I saw sprouts to water again. Your potting soil should have enough moisture to tide the tuber over until it sprouts.

Does it already have eyes or sprouts on it? Did you completely cover the tuber or are you leaving the eyed or sprout uncovered to monitor it?

No worries... Just let it dry out a bit, and make sure the potting mix doesn't get either sopping wet OR bone dry.

The 'no water' mandate is a general bit of advise to play it safe. If you planted in dry potting mix, without moisture your tuber wouldn't put out any roots and wouldn't grow, so you did right.

When I planted my first one back in March I got so impatient to see the sprout, I dug some of the dirt out and let the top of the tuber exposed so I could watch it.

Your beauties will sprout before you know it. :)

Exposing the head of the tuber can cause it to dry up... It's a pet peeve of one of my dahlia mentors that people do that, then complain to him that the tuber they bought from him didn't make it. He always recommends covering the complete tuber with a layer of potting mix.

However, in my experienc, the hearty varieties with invincible tubers can be abused this way with little consequence.

LOL!
I can see where that would be a pet peeve. All of the sources on "how to grow dahlias" said to leave the tip uncovered.

Hmm... No source that I've read... Some folks keep it uncovered to make it easier to take cuttings, but moisture in the soil helps the tuber break dormancy and encourages sprouting, so there's not much reason to leave it exposed otherwise. It breaks though the soil quick enough when it's ready.

Honestly, I don't think it makes much difference, but this gentleman has thirty years of experience on me, so I am inclined to listen and make it a habit if I have the choice of covering or uncovering the head. I don't feel as if I need to test this grain of wisdom he's shared, as I'd rather play it safe and be patient then lose a much-coveted variety I'm looking forward to seeing bloom.

SRY DON'T KNOW HOW TO START NEW DISCUSSION AND I HAVE A DALHIA QUESTION... I'M A NEWBIE.TP DAHLIAS... I PLANTED 2 DAHLIAS 2 1/2 FT FROM EACH OTHER... 1 OF THEM IS DOING GREAT @ ALMOST 2 FT TALL ... THE 2ND ONE WAS GROWING GOOD TILL 2 WKS AGO WHEN 1 OF 2 STEMS AND LEAVES STARTED DROPPING AND THE ENTIRE PLANT STOPPPED GROWING @ 8"... THE 3RD TUBER PLANTED ON OPPOSITE SIDE NEVER ROOTED... THE SOIL WAS AMENDED W/ MG GARDEN SOIL...HUMUS... COW MANURE AND MUSHROOM COMPOST... GARDENING FOR 40 YRS... ANY ADVICE WOULD BE GREATLY APPRECIATED... THANK YOU SO MUCH...

@Gail

Please use complete sentences and for goodness sake turn the darn capslock off. There is no need for all capital letters and it is incredibly annoying (it is like you are yelling in the form of typing).

Now, about your dahlias:

Check the stems to see if anything is boring into it. If no evidence of holes leading in, dig that plant up during a cool time of day and check the tuber clump for rot. I am guessing that one stem has roots and the other is more attached to a rotted tuber. If a rotted tuber is found, put on a glove and pull away as much rotten part as possible. Give it a good spray with the hose and replant it and water *moderately*. It sounds like you are using a ton of compost, so I would tone that down a bit until the plant is really growing strong again. You may want to let the plant grow on in a well-drained pot for a bit before plunking it back in the ground to let it build up a good root system. Whatever you do (ground or pot), water Moderately to avoid further rotting and do not let it dry out completely to avoid stressing the plant.

The third tuber might be a goner, only way to tell is to dig it up and look. All dahlias have to have a bit of crown (sprouting area where the previous season's stem was) to grow. If it doesn't have a crown, nothing will grow. If it does have a crown and isn't rotted try putting it in lightly damp potting soil and keeping it in the house where it is nice and cool for a bit until it sprouts. Then plant it back outside on a day that isn't sweltering summer heat.

@Everyone else

I agree with the dahlia guy that they should definitely be covered completely with soil. As long as you don't overwater, all is well. The extra soil to burst through will make for a more upright and sturdy stem that needs less staking as it will steady the plant better. If no growth after planting for a good three weeks, then sure, dump the pot out or dig up the tuber and investigate.