How to encourage roots from callus tissue

[gray]

In doing some apple hardwood cuttings this year with bottom heat. Thay produce callousing but do not generate roots

Any advice please. What am I do ing wrong or am I too eager

[blackcurrantNV]

When did you stick them? I’ve heard that fruit trees can take a couple months before they have good root formation, especially if it’s a harder to root variety.