If you say "pumpkins hardly bruise", you mean they don't OFTEN bruise because they have thick skin (or rind).
You could also say "Pumpkins seldom bruise".
When people talk about getting bruises on their skin, they say, "I don't bruise easily" or the opposite "I bruise easily".
It would sound natural to say the same with pumpkins, "they don't bruise easily".
Hope this helps