How large of a hole for fruit tree and lilacs?

[Aaron in MT]

I am in Montana in a 4a zone. We live in a *very* rocky area. The winters are long. It is a rough place for plants.

We had a small maple tree in our yard that died. We replaced it with an apple tree. The apple tree partially died the next year (some of the branches turned dark and hard and no longer produced leaves). This year it is completely dead. We are going to replace it with another fruit tree. We will also be planting additional fruit trees and several lilac plants (https://www.provenwinners.com/plants/syringa/bloomerang-dark-purple-reblooming-lilac-syringa-x).

We will dig the holes larger and use better soil this year. However, I am not sure how large of a hole to dig for these plants. What size would you recommend for the fruit trees? They will be small, but I want to make sure they have some room for the roots as they grow. And how large for the lilacs? They are coming in a gallon size.

Also, any tips on keeping them alive?

Thanks!

 

[Mr_Yan]

Well take this with a grain of salt, I've never lived colder than zone 5.

I never bought into the idea of greatly improving the soil for a tree you're planting. As I see it the roots will tend to stay where the nutrients are so they'll tend to that small area you improved. I want trees with strong large root systems. That said I've only ever dug holes just large enough for the root ball to fill. In the last three years my track record is 14 and 1 (lived / dead) when buying trees from the good nursery locally and 1 for 5 when buying from the big box hardware store nursery.

Are you going with a good nursery and local-ish to your climate?
Are you planting at the right depth?
Are you planting the tree and walking away for the year?

I do baby my trees for the first summer. Make sure they're getting deeply watered each week through the hot part of the summer. I take a 5 gallon bucket and drill a 1/4" hole at the edge of the bottom. Place the bucket next to the tree and fill it with water each weekend - cheap lazy way to trickle water a tree.

You said rocky soil. Are you a few inches of soil over solid rock ledge? Do you need a pick-ax to dig the hole. If so you may not get much of a tree planted.

 

[Aaron in MT]

I do use a pick axe to dig a hole. I dug our garden with a pick axe. 10x60', 1-1.5' deep. Took me a year. But they do have trees here. So it must be possible. The trees they plant in the park nearby often die as well. However, the aspen trees invading our yard from our neighbor thrive.

The apple tree was from a local nursery. I didn't give it any special soil. I dug a hole large enough for the root ball. I buried it to the recommended depth of a few inches below the splice. It did so well the first year and first winter. The trouble started when we received a massive snowstorm in May, after it had its leaves. Following the snow storm, the central branch died and it never recovered. I was hoping there was something I could do differently to protect the next trees.

The lilacs we are getting are supposed to do well even in 3 zones. I want to give them the best chance possible as well. Do you think I should dig a larger hole for roots to grow wider?

 

[Mr_Yan]

What about flipping this on it's head and get smaller trees. Let the tiny seedling grow into the area as the local forest does. This also increases the root to top ratio of the plant that is going in the ground.

Then look at the micro climate of where you're planting. Can you place these where, say, they're protected on the north and west with good southern exposure. Is there an area where snow tends to drift in the property but leave another area bare?

Aspens are a weirdish one as they're all connected in one root system as one large organism. This is why you see a whole hillside of aspen turn yellow and drop leafs at the same time in the fall - it's really one tree.

The lilacs I remember planting here were bareroot and about the size of a pencil. They thrived.

 

[cpp gardener]

Choose varieties that are hardy in your area. If they can’t take the cold it doesn’t matter how you make the hole.

Dig the hole twice as WIDE as the rootball but only as deep as the rootball. You don’t need to add anything to the soil. When it’s i, give it a good soak ( I flaunt current thoughts and use liquid fertilizers ).