Garden soil too hard
 

I built a little box to grow some vegetables and used a mix of mushroom manure and topsoil. I'm thinking I should have mixed some peat in there too because the top layer gets pretty hard over the course of a sunny day.

Is there anything I can do now, after I've already planted the seeds, to loosen the soil up?

Side dress and mulch with dried leaves and add worms. It's not much of a solution since it takes massive amounts of organic matter to change soil composition, and worms are slow, but 90% of gardening is the prep. If the Ph is off, that will cause the soil to harden too.

Mushroom manure, does little or nothing for growing things, mushrooms take everything out of this stuff. It,s great for top dressing as it keeps the weeds down.