planting in clay soil
Hello and thank you for contacting us,
You probably already know that clay soil can be a problem for some plants, and there are a couple of reasons for this. First is that clay soil does not always drain well, and in low areas of a landscape, water may pool for long periods of time, drowning the roots of the plant. The second problem is that clay soils are prone to compaction, and compacted soil may not allow roots to grow properly. This can mean stunted root growth, or in extreme cases, plant failure.
If the soil doesn't drain, and there is standing water in the area, the blue spruce may not survive those conditions. Assuming that the soil drains, these trees have a better chance to establish and thrive. One way to test drainage is to follow the procedure outlined in this publication: https://extension.tennessee.edu/Williamson/Horticulture/Consumer%20Horticulture/DIY%20Soil%20Drainag.... This will help you confirm that the trees will survive at the planting site you have chosen.
When it comes to planting trees, you want to make sure that the root flare (where the trunk widens out into the roots) is not below the soil grade level. This will stress the tree and could lead to failure. For a step-by-step guide, follow this link to more information: http://cru.cahe.wsu.edu/CEPublications/FS047E/FS047E.pdf
The heavy clay soil at your site means that your planting hole should be modified from the instructions in the publication. Instead of 2-3 times as wide as the root ball, you should dig the planting hole five times as wide as the root ball. You will dig a shallow hole, only as deep as the root ball, just as it says in the publication, unless the soil drainage is poor. With poor drainage, you can plant even shallower, so that the root flare is 2-3 inches above grade. If you have to plant it higher because of poor drainage, then it is important to put mulch 2-3 inches deep around the tree, covering the root ball, but keeping it at least 2 inches away from the trunk. Wood chips make a good mulch and are inexpensive.
Young trees need care, especially in the first 2-3 years after planting. You can find more information about this at the following link:http://extension.wsu.edu/spokane/wp-content/uploads/sites/33/2017/07/C118-Tree-Care-15a.pdf
Please let me know if you have any questions, or if I've confused you. I'll do my best to help you get your trees off to a good start! Thank you again for contacting us.