Mara,
Critical nutrients for fig growth and development also mean a LOT to all sorts of cabbages.
Those with so nice growth on your Marabout big pot, sooner than later, will destroy your fig, depleting the soil of the basic nutrients for fig growth
You decide, but I would never mix those two plants, regardless the size of the pot
The time is right , now, for an overhaul of the present state of affairs...
uproot all collards (*), and change the old soil to whatever you decide, enrich it with the good nutrients and mulch organic (light colored wood chips for instance)
( collards may also have invited some little pests and parasites feeding on their tasty roots ... fig roots seem to be rather sweet as well !) - see what I mean ?
(*) Try 'caldo verde' our popular and low calories broth made with collard thick leaves very rich in calcium, iron, magn, P, K, etc.. collards have twice the calcium content of cow milk!
Francisco
Portugal