It’s apple picking season. Like most other people I love fresh apples and nearly everything we make from them. Like many of you I also have a few in my backyard. Mine are semi-dwarf types. We can also purchase standard and dwarf trees.

So, why do some grow 30 feet tall and others reach maturity at only five or six feet? It has nothing to do with the apple cultivar. We can find Granny Smith, Rome, or Pink Lady in any height range.

Apples and most other fruit trees aren’t propagated by seed. They are grafted onto some type of rootstock. The rootstock, or sometimes an interstem, determines tree size. Interstems can be used to dwarf trees with existing non-dwarfing roots.

Essentially, the lower part of the tree controls its height. The upper part controls fruit type. We call the bottom part the stock and the top part the scion. What we are doing is combining the desirable tree size of dwarf trees with the type of fruit we want.

In the case of interstems, we can take an existing standard sized tree and convert it to a dwarfed one by grafting a scion from a dwarfing rootstock onto it. Then we graft the desired fruit cultivar onto the interstem. We could graft several different cultivars on the same tree if we wanted.

The result of grafting a desired scion onto a dwarfing stock produces a combined organism, but it’s not a genetically modified one. I repeat, grafted fruit trees are not GMOs, not that it would necessarily be a problem. The rootstock and scion grow together but the fruit is entirely that of the scion. All the resulting apples are clones.

So what happens if you plant apple seeds? It’s hard telling since they would be a cross between two different types. Some seedlings might be pretty good. That’s how we develop new varieties. We cross two types and evaluate the results. The resulting seedlings would not inherit any dwarfing characteristics though.

Grafting is an extremely old technique. It’s been around for centuries. Horticulturalists have dwarfed apple trees commercially for nearly a hundred years. Dwarfing is not the only reason we use rootstocks. Some rootstocks offer disease resistance, greater drought tolerance and winter hardiness.

Dwarf trees have many advantages over standard sized trees. They are easier to prune, spray and harvest. Simply having everything closer to the ground makes them easier to inspect. It’s also safer to perform any of these chores when you’re not standing on a ladder or climbing a tree.

For the homeowner with limited space, several trees could be planted instead of just a couple. Dwarf fruit trees also begin producing at a younger age. Being smaller, they might also blend into the landscaping more effectively. Additionally, dwarf trees can be planted in containers for patio use.

I know it’s cheaper to buy them at the grocery store or farmer’s market, but growing our own fruit can be rewarding. Sometimes harvesting only a few is worth it.

Ted Manzer teaches agriculture at Northeastern High School.