This is why I use a rooting inoculant on my plants.
This is the roots on a 2" tomato sucker
two weeks after inserting it in the rockwool.
I started about 15 of these tiny suckers which grew very quickly and were transplanted into pots. They continued to grow quickly outside. I gave most of them away the first week of June. I kept a few for myself so I could watch them grow. They are huge tomato plants and are putting off their first flowers.
To answer a questions about the picture:
I used net cups to keep the rockwool cubes upright.
I use rockwool only for the tiniest suckers.
I root larger ones in water or soil. I'll share picts soon, if I can. Life is super busy.