You are almost certainly keeping them too long in each pot size, if some of them have spent 4-5 years(!) in the same (small) container. Most root growth is in autumn, repot now and you may see more top growth next year than if you had waited until spring.

If you are going to try to really keep on top of it, repot when the roots approach the walls of the pot. Roots coming out of drain holes indicate it is already late. Roots growing into the ground indicate it is WAY too late.

Hi,

Three years is just about pushing it. If the roots are okay the soil probably isn't. Most potting soils are high in organic matter and breaks down over time. The ideal repotting interval for *most* plants is every two years. It's probably a good bet that when you take the trees out of their pots they'll hardly have any soil around the lower roots. It's best to repot during the cooler times of the year; in spring before buds swell or fall after leaves have fallen.

Since it's been awhile you may have to prune off roots that have girdled around the pot and root ball. You can pot up to the next larger pot size, or using a more advanced technique, root prune more of the root ball to keep it in the same container.

Bonsaists do this to keep their trees in the same pots. Any good book on bonsai will show you how to do this as well as state all related precautions in doing so. Trees can be kept in the same pot for decades or even centuries with regular and proper root pruning. Although major root pruning is more advanced it's not difficult.

Layne