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.

Answer 2

I live in zone 5 in a high mountain desert climate in SE Idaho with lots of wind. Our soil is alkaline, usually ranging in the 7.8 - 8 range. If you pour vinegar on our soil, it will start to fizz. That shows how much calcium is in the soil. Great for potatoes but not so much for conifers - it makes it difficult. I have tried many different kinds to see what I can get to work. All my trees are on a drip line and that has been the key to making sure they survive and some even flourish. I've tried some that I knew from the start would struggle (Fraser Fir) but I wanted to try anyway.

The best has been Colorado Blue Spruce. Most have been from bare-root plantings but I have done a few via pots. The potted trees survive easier but if I don't plan the bare-root Blue Spruce too late in the spring, it does just fine. Note, I can plant bare-root deciduous trees much later and have them do just fine. But the Blue Spruce does not handle transplanting in the heat at all. But once established, they grow well. Early on I only got 6" of growth/year but now I'm getting 12 - 18 inches/year.

Others: Ponderosa Pine - Only got 2 to grow out of 10 seedlings but once established doing OK. Not a fast grower - about 1/2 the rate of the Blue Spruce. White Pine - no luck Concolor Spruce - At first, they all died. I think they have to be potted or planted really early. A few have lasted two years now but growth has been slow. Fraser Fir - lost most about five are growing for the past 8 years. Growth is really slow 4 - 6 inches/year. Austrian Pine - planted 5 from pots. All 5 are doing well. Growth is like the blue spruce. I should plant more of these but they don't fill in as well as the spruce and most of my trees are part of windbreaks. Norway Spruce - tried, failed. May try potted or plant earlier. They are supposed to do OK.

Also tried Canaan fir and Douglas fir without any luck. May have been planted too late in the season.

Tamarack has survived one season. Arborvitae grow well in the area but they are not my favorite but I'm 1/2 on them.