I would at the very least till in some composts. If your soil is lacking in organic material it's gonna be a hard life for the MJ. Chicken manure for compost and pelleted chicken manure for dry fertilizer down the line are probably the strongest cheapest options if youre ok with animal product.

You'll need to really be careful about overwatering when dealing with plants in the ground. On the upside you can typically water less. You should get a feel for how fast the top layer is drying out, maybe the safest thing to do is to underwater and try to see how long it takes for the leaves to drop and then water them. This timing will change depending on the size of the plant and the weather. Overwatering will clog the roots and give them root rot, which will kill them without any way of stopping it once started.

Get it in the ground asap if you want flowers!