Some property owners are growing a new kind of crop on P.E.I. — black walnut trees.  Jesse Argent owns Havenloft Tree Nursery in Charlottetown, which specializes in growing black walnut trees. His company grows the saplings and sells them to property owners as long-term investments.  “The timber value is incredibly high, as well as the crop that can come down from the tree. The nuts themselves are actually highly valuable per the pound as well,” said Argent. …”There’s a huge amount of land that’s just not being used or [is] underutilized on P.E.I. and it’s just a great way to increase land value,” he said.  But the investment isn’t without its risks and challenges — Argent said it takes years before growers can harvest the trees for nuts or wood. The trees also produce a toxin known as juglone, that can make it difficult to grow some types of plants nearby.