When can I plant a tree?

Roots run deep when talking about timing

Dear Donna,
"I appreciate all of your gardening work, and thought you might be able to help me with a general question I have (or perhaps guide me to someone who can; so far a web search has not been successful)? When, roughly speaking, is the best time to plant trees in Calgary? Spring or fall? If spring, are we talking early spring – i.e. beginning of April, or more like the end of May?
- Joe K

Dear Joe,
With exceptions, I would plant trees in Calgary when the soil is thawed fully in spring from May into June. This gives the tree a chance to root more efficiently and benefit from our normal spring rains.

Of course, there are reasons to plant at other times. Some experts even argue that any tree planted six weeks before the soil freezes in the fall has time to establish and grow. But who knows, for certain, when we will get a soil-freezing frost in Calgary? Soil can freeze solid here any time from early October to late December.

Unless you want to take advantage of seasonal sales or need to get the landscape planted now for winter resale of your home, wait to plant trees until spring. By the way, there is a better chance of evergreens surviving fall planting than deciduous trees, so that may also be a consideration.

Once you buy the tree and bring it home, take it out of the pot and look for the natural tree flare above the roots.

This is where a tree should be placed in the soil. If it is planted lower than this root-trunk junction, the roots might suffocate. The deeper the soil is over the roots, the lower the oxygen levels. If the tree is planted higher, the tree roots will be exposed, dry out and die.

In new subdivisions there is often only 10 centimetres of good soil above really bad, high-pH, compacted clay soil. If you simply dig a hole and amend that hole with soft soil for the new tree, you will get what I call the bathtub-planting crisis. Inside the hole, the soil will be soft and improved, allowing the water to move into the "bathtub" easily. But outside the hole, the existing hard clay soil will be super resistant to water movement. And after the hole with good soil fills up with water, the moisture can't drain away and the roots, left sitting in the bathtub of water, will drown.

So amend the entire site before you plant trees. First, contact a bulk landscape supplier and order enough amended loam for the entire planting area. Because most tree roots will be in the top 30 centimetres of soil, it is ideal to add this depth of topsoil. After planting and before watering, pile a five-centimetre donut of extra soil about 60 centimetres away from the tree trunk so the water doesn't flow away too quickly once rain or watering begins.

Newly amended soil has all the nutrients the tree needs, but I like to water in with a root-starter solution just to be sure of success. I use Wurzel-dip, available in Calgary at Professional Gardener, to boost plant growth. I have also seen various organic root stimulators containing kelp and extra B vitamins at various garden centres. I find these solutions can, and do, lead to faster rooting come spring.

The final step is to add 15 centimetres of bark or ground wood chip mulch to the entire planting area. Be sure to carefully pull back mulch away from the tree trunk so it doesn't start to decay living material.

Donna Balzer is a garden writer and entertaining speaker. Sign up for her blog feeds at www.gardenguru.net or follow her on twitter @NoGuffGardener.

Tagged: Donna Balzer | Gardening | Guest Column | planting