Growing Things: Conquering clay problem to help ornamental trees thrive

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Q: I planted two two-meter junipers three years ago and they haven’t grown at all. There are only a few branches that have brown needles, but for the most part, they seem healthy. I also planted six spruce trees almost seven years ago, that range in height from 60 cm to 2 m and they also seem healthy but have not grown.

We had very little topsoil and the ground is very, very hard clay. I planted them according to the directions they came with. Dug a big hole, mixed some clay with good soil, fertilizer and compost. All of the trees get lots of sun. The junipers, since they are in the lawn, get lots of water, whereas the spruce only get rain. Do you have any suggestions to help get these trees to grow?

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A: The problem is very likely the clay you have described. It sounds like you planted them correctly except for perhaps one thing. I would not have mixed the clay with the topsoil you were adding. It might have been best to remove the clay completely from the planting hole and replace it with only topsoil and compost. This would have given the trees a good start before they encountered the surrounding clay.

In a situation such as yours where the clay is present in large quantities and is also very compacted getting ornamental plants to grow is very difficult. The best thing you could have done from the beginning was to remove all of the clay to a depth of 20 – 35 cm and replaced it with topsoil. Since this is likely not possible to do now adding compost each and every year to the base of the trees and the surrounding area will help somewhat. Dig the compost in as much as you can.

Since the junipers are in a lawn setting this makes the addition of organic matter to the areas surrounding the trees more difficult. Having said all this if you are patient and diligent with adding organic matter you can improve the soil structure.

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The next problem that may present itself is that the trees may show signs of distress if we get a wet summer or spring because the water is not able to drain away from the roots due to the clay problem. I wish I had a more positive solution for you but because the landscape was constructed on clay this makes for very difficult growing conditions. All you can do is hope for the best unless you are willing to remove the clay and start over. As for the spruce, I would be supplementing their water and not relying only on the rain. They need all the help they can get.

Every week, Growing Things Outdoors runs online at edmontonjournal.com or, if you prefer an epaper format, epaper.edmontonjournal.com

Learn more by emailing your questions to [email protected], reading past columns online or my book Just Ask Jerry. You can also follow me on Twitter @justaskjerry01.

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