I have a situation...

The first Dahlia I planted in a pot, it was planted upside down but, the plant is doing just fine and has now grown pretty tall in couple months (considering it circled the whole pot underground trying to find a way)... almost 2 feet and has nice big leaves. I topped it after 4 sets of leaves and now it has nice bushy structure.

Now, the problem is with the other ones. I planted them properly in pot and covered the tuber with soil and left a lil' bit of the sprouts above ground to see the growth. I heard Nitrogen helps them so, based on some advice from folks I put in some lawn fertilizer and lil bit (half teaspoon) of osmocote+ in the pot w/ the tubers. After 3 weeks, the some of the sprouts look reallllllllllly small with couple of them barely showing any growth.

Worried.. I dug them up neatly w/o hurting the feeder root and then washed the tubers with water very softly and then changed the soil in the pot with normal potting soil with lil' amount of bulb tone from espoma. I am now watching them and hoping I have not completely destroyed the tubers.

Has anyone experienced something like this? If it helps, the first dahlia (planted upside down) was Akita and the others w/ growth problem are Ivory Palaces, Cornel, Canoz Anne, Ms. Julie, Hana Hitosuzi, Ruskin Andrea.

Appreciate your feedbacks and suggestions as always.