In response to my earlier post on Italian Stone Pines, I received the following question from a reader in Allen, Texas, just outside of Dallas:
Just saw your blog re: Pinus pinea. I bought one (small) tree from a nursery over the Christmas season. It is currently outdoors in a medium-size pot. Can I plant it outdoors, but keep it pruned so it doesn't get to full maturity? I’m just not sure we have a good spot for it to reach that size. The width is what I am more concerned about. Is there a way to keep it in a container, or more "dwarf" sized like a spruce? I wouldn't mind some height but it wouldn't be practical for the width to be even 20 ft probably. KarlaGood morning Karla,
For the sake of a clear conscience, I have to repeat the cardinal rule for planting trees: never plant a tree that has the potential to grow too large for the space in which you are planting it. From your question, I'm pretty sure you already knew that, but I had to repeat it.
OK, now on to your question.
If you don't have the space for the mature tree, then I would recommend that you try to keep it in a large pot. If you plant it out into the ground, you will be in a constant battle to reduce its size and limit its growth. In the ground, the roots will grow unfettered, and that will push the top growth. Then you're stuck with a tree that is trying to grow big while you're trying to keep it small; the end result is generally not too attractive.
If you put the tree in a large pot instead, you have a better chance of controlling the growth and ending up with an attractive tree – perhaps even something like a large bonsai. In a pot, it's fairly easy to keep a tree small, because its root space will be restricted and that will have a definite dwarfing effect on the tree. Then you can do some minimal shaping in order to balance the size of the top against the size of the roots.
When you get to the point of pruning the tree – and start early, so it doesn't get away from you – keep in mind that pruning pines is unlike pruning almost any other plant. With most trees, if you cut back a branch it will re-sprout from a bud near the pruning cut. Pines, though, have only one growing tip per branch; if you cut off this growing point, the twig or branch will die back all the way to its point of origin.
With pines, we prune the branches before they even form. Each Spring, you will see the new "candles" forming on the pine tree; that's what we call the expanding buds. When you want to limit growth along a particular branch, you pinch back that candle when the needles first start to expand out of it. You can pinch it a little, half-way, or all the way back; how far you pinch is how far you will limit the growth, and that's where the new growth buds will form.
Now you can see why it's impractical to prune an Italian Stone Pine to limit its width: you'd be up in the sky on a ladder each Spring pinching back 47,000 candles, and I suspect that living in a major metropolitan area you can find better ways to spend your time.
So, plant your tree in a large pot with a good soil-based potting mix, and pinch it back to maintain a decent size and shape, and you'll probably end up with a very nice tree. As with all potted plants, be certain that the irrigation water is going through the soil, and not down the edges of the root ball, and never let it sit in a saucer of standing water.
I hope this helps,