Myself, I do add a weak mix of fertilizer to them after they are potted up to larger container. Some say not to because it will burn the roots but I never had problems and I know a few others who do the same as I do. I would say go for it just don't use a strong dose and you should be fine.

I do fertilize them. But I use a fertilizer with low nitrogen the first number. Generally low nitrogen fertilizer is my the one I use for all my fig trees. When I can not find low nitrogen fertilizer I use 10-10-10.

Yes I read the article, she said that sandy soil is deficient in phosphate. That what we have sandy soil. Even in pot soil I add some sand to help in drainage. Buttom line I read a lot of articles of those so called experts and every one is say some thing different. To eliminate this confusion I use balanced fertilizer 10-10-10 Too much nitrogen especially in Figs gives you a lot of foilage and leaves and less fruits. If you have the tree as ornament too much green will be fine but I want to eat some figs.

I use slow release fertilizer with ratio 3-1-2 on reported small rooted cuttings and I get great results. I think the slow release is released a little at a time.

Bass

Not sure I agree that nitrogen reduces the number of figs.

Pretty sure Belleclare recommended Miracle-Gro (24-8-16) for figs. Since their site was taken down, if I remember correctly, they said once a month, 2 tbls to a gallon of water (MG recommends 1 tbls to a gallon).

I think Nitrogen increases growth = more nodes = more figs

Nitrogen increases the distance between nodes,so on a 3 foot stem you have less nodes,than if the nitrogen was not given.!
Belleclare advice (24-8-16),is too rich in Nitrogen.
This advice is good for producing large tall plants fast,so they can be sold for a better price,but once the plant is in the gardener possession,the nitrogen should be reduced so the plant grows solid wood,to resist Winter,in special ,in cold climates as northeast.

You may have less nodes per foot but more nodes overall.

I don't fertilize my in ground trees only my potted trees which over winter in the garage.