It seems that your rootstocks are more vigorous than the scions and will
continue to send out suckers. The graft should always be at about nine
inches clear of the ground. Any growths from below the graft must be removed
on sight or they will quickly become dominant. Keeping them removed might
stop more forming after a couple of years.
By "Crab apples" I assume you mean apples grown for their flowers and
eventual decorative fruit? [Rather than being grown for Cider] These tend
to prosper better on the MM106 and can show your symptoms if on one similar
to M25.[for Cider/Crab apples]
Your supplier should be able to advise.
Best Wishes.

"XDeus" wrote in message
m...
I just purchased 6 crabapples and was wondering if there is a problem
with planting them with the graft underground. A couple of them have
big, ugly rootstock stumps with what looks like a lot of pruned
suckers. Is there a problem with putting that section underground?
They range in length by 2 to 4 inches.