It is always best to start seeds outside. Right now though in my area it is to hot to start anything. Seeds like certain temps for germination. If you were to move your seeds outside now you will need to harden them off. That means that you will need to slowly get them use to the different atmosphere that is outside.

In regards to the wilt it could be several things it could be a pest. It could be lack of water. It could be to much water. I try my hardest to always water any of my seedlings from the bottom. Seedlings outside take more water than those that are inside. I am not familiar with a cocount husk planter, but any planter needs venting holes at the bottom. I would suggest maybe putting your husk in something like a bowl or a shallow dish of some sort, place your husk in a window, water by adding the water to the dish. As the water dries up then add more water if your leaves start to turn yellow slack up on the water for a few days.

This advice is given as thinking that your plants didn't suffer root rot. Look at your seedlings closely if they look like they have been actually pinched, then sorry there is no hope. If there is no pinch mark then your plants are only wilting for the lack of water and sunlight.

Here is a link that might be useful: How to harden off your plants

Here in Texas they had no problem sprouting in the summer and are self seeders. Never worried about the soil as if they will grow in Texas soil they should grow anywhere. Have you any friends who are growing a Rose-of-Sharon Bush? If so ask for a small cutting and dip in root-tone and pot. When it sprouts enough stick it into the soil and let it grow. Even here I had no problem getting them to grow and they were sent to me by a nice lady here on this website and they came in the hot weather and I thought I had lost them as they looked like they had been steam cooked in the mail. I know they even grow in Michigan and make better bushes than here in Texas. They grow more like a dwarf tree.
Paul