The Gardenia and whatever's in the third picture look very unwell - I'm assuming its the soil they're growing in, because that's what it smacks of. If you used Miracle Gro moisture control potting mix, that's already balanced, so doesn't need dolomite added to it - this addition will have reduced the ph and Gardenias like acid conditions. I can't tell what variety of Gardenia its supposed to be, but they're not called prima donnas for nothing - they like even, relatively high temperatures, no draughts, don't like to be moved, must be watered with tepid water, as well as acid soil conditions.
You probably would have done best just to use the Miracle Gro as it was for all the pots - something's out of whack with the soil conditions so the plants are remaining static. The dolomite has probably upset the balance - although its used in many potting composts, its largely because the compost has been based on a high peat content, so dolomite is added to raise the ph and allow better uptake of magnesium and calcium by growing plants. If it was already a balanced ph, you may now have knocked that out of whack and so the plants can't take up the nutrients they need.
Regarding the seedlings - if you didn't use potting compost for seeds and cuttings, but instead used the same Miracle Gro as for the pots, this is too strong, has to much fertilizer in it and burns the seedling's roots. Given you also mixed regular Miracle Gro potting mix with dolomite, that might explain the poor results.
I'd buy some more potting mix, unpot the plants, shake off what soil you can without breaking roots, then repot into the new potting mix - you can add perlite if you want, though its not essential, given this mix is 'moisture control'. And don't feed for a while - I believe one of the claims for this potting mix is the fact you don't need to feed plants for six months - if it is, don't feed for six months.
I'm somewhat curious as to what the orange deposits on the Pothos are - they look as if you've split builder's sand.