What evergreens will tolerate alkaline clay soil in USDA zone 4?

Question

Although the area where I live is famed for it's white pine they grow in sandy soils. My garden has a thin skim of topsoil over six feet of compact alkaline (ph 7) clay.

My dwarf white pine is doing so poorly I think I may have to replace it. Are there any evergreens aside from cedar that will tolerate alkaline clay with full sun?

Climate USDA zone 4 with lows to -30 degree Celsius and highs of +30 deg Celsius, full sun, large greedy cedar hedge close by, southern exposure

2022 Edit: a better phrase for the soil I have is "Marine Clay". The White pine succumbed to a white scale type insect. Deciduous shrubs have done much better. The evergreens that have done well are Taxus (Yew), Thuga (Cedar) and Tsuga canadensis (Hemlock)

Answer 1

Not many conifers apart from junipers/arborvitae that will thrive in alkaline soil. There are some broad-leaved evergreens that will live.

The alkalinity of your subsoil means more maintenance, but doesn't mean you can't successfully grow acid loving plants on top. Acid loving plants have an underdeveloped root system, and obtain nutrients from symbiotic bacteria/fungi that thrive in acid soil, so these plants don't do well in too high pH, and show signs of nutrient deprivation, even when fertilized.

And also of note: most acid-loving evergreens have very shallow root systems, so if you can provide a highly organic, acidic layer in the top 6" of soil, and feed it with compost, and/or fertilizer (organic is more effective in this case), you can grow very nice conifers.

See here for more info.

If you aren't able to do this, I'll make a list of evergreens that will grow in a soil pH of 7.0, in zone 4. There aren't many that come to mind.:

• Boxwood, Buxus sp.

• Spindle, Euonymus sp.

• Juniper, Juniperus sp.

• Arborvitae, Thuja sp.

I've left out the cedars (genus Cedrus) as per your question. However, these do not grow quite as well as Thuja in alkaline conditions anyway.

Your soil are wrong for most coniferous evergreens, and the hardiness zone is wrong for most broadleaved ones. If none of the listed plants will work, and you cannot work on the conditions as described above, you may have to leave evergreens and plant deciduous shrubs/trees instead.