Written by s • Trees and Shrubs for Alkaline Soils – Part 1
The Right Plant in the Right Place is a slogan that you will often hear from professional landscape designers and horticulturists. It’s a simple principle, but one often ignored in the rush to have That Loved Plant in This Important Place – a principle often followed by home gardeners. It can be hard to accept that the plant we want is simply not going to thrive – or even live – in the place we think is ‘the perfect spot’. Plants are alive, and they have needs if they are to thrive. Each one is different, because it evolved to fit perfectly into its home – which in the case of our garden plants could be 12,000 miles away from where we want to grow it. Of course, distance is the least of our worries, because what makes a ‘Place’ is mostly about seasonal temperatures, light, water and most importantly, soil. It is difficult and often impossible to change the conditions in the places that make up our gardens, especially when it comes to soil. That’s why it makes a lot more sense to seek out that ‘Right Plant’ for what you have, rather than trying to crowbar the plant you want into a slot where it will only be unhappy, underperform, and in the end only make you more miserable.
Is Your Garden Soil Acid or Alkaline?
The acid or alkaline balance of your soil – what pros call ‘pH’ (‘pea-eitch’, not ‘f’) – is a complex issue that involved hydrogen ions, but for gardeners it’s a fundamental piece of information about your garden soil that should be the first thing to find out. Luckily there are simple kits or meters you can buy that will tell you almost immediately what your ‘magic number’ is. Pick one up and check out your garden. If you have a larger yard, take readings in several areas, especially if you have a sloping garden. The reading will probably be between 4.5 and 8.5, with values below 7 being ‘acid soil’ and numbers above 7 being ‘alkaline soil’. Now you know what you have, so read on. . . .
The Plant I Love Doesn’t like My Soil pH – What Can I Do?
It’s true that we can make big changes to the nutrients and water-holding of a soil by adding organic materials like compost, and by using mulches, but we can’t change everything. It is one of those quirks of nature that it is easy to make your soil more alkaline, but darned near impossible to make it more acid. If you have acid soil, but need something more alkaline, for a vegetable garden perhaps – then adding garden lime in the correct amount in fall which usually raise it significantly by spring. While you might read lots of advice on making your soil more acid, it almost never works, and certainly not for long, so don’t waste your time – put that lovely acid-loving plant like an azalea or blue hydrangea into a pot with suitable soil. There. Problem solved.
Choosing Trees and Shrubs for Alkaline Soils
Many familiar trees and shrubs are happy in all but the most harsh alkaline soils, but some are especially suited. Let’s look at some trees this time, and in our next blog we will talk about suitable shrubs to fill our the beds in your ‘alkaline garden’.
Trees for Alkaline Soils
If the pH of your soil is 6.5, you are in garden heaven, and you can grow a wide range of plants. Most ordinary plants will be able to cope if it is 7.0 (neutral), but over that you need to seriously take notice, and focus on growing plants that tolerate or enjoy alkaline soil conditions. Forget about planting a red maple, and plant instead a red chestnut tree. There are lots of trees that grow happily in alkaline soils – here are some ideas:
Red Chestnut Tree (Aesculus x carnea): The big rounded leaves, divided into 5 or 7 separate lobes, make this an instantly recognizable tree, and it is one of the most spectacular flowering trees you can grow. May is the time of year it will be covered in 8-inch upright clusters of bright red flowers and this ‘knock your socks off’ display makes up for the lack of brilliant fall coloring. Don’t be tempted by the chestnuts it produces in fall – these are not the edible ones you might know. Hardy in zone 5.
Katsura tree (Cercidiphyllum japonicum): With probably the best fall color of any tree suitable for alkaline soils, this Japanese native tree will reach 40 feet, and its heart-shaped leaves color orange, red and gold in fall. A great lawn specimen hardy even in zone 4.
Linden (Tilia species): All the different species and varieties of linden are excellent choices not just for alkaline soils, but for urban gardens and harsh conditions generally. If you like a neat pyramidal look on your trees, you will love Linden, which is also called basswood, or ‘Lime’ in Europe, because of the citrus scent of the green flowers in early summer. Little-leaf Linden, Tilia cordata, is easily the most fragrant, and hardy even in zone 3. The Basswood, or American Linden, Tilia americana, has fragrant flowers too, and the dried flowers make a delicious late-night tea. Don’t plant Linden over driveways or patios, as they can be messy with leaves and falling flowers. Best to plant at the back of your yard, over beds or grass.
Ironwood (Ostrya virginiana): For a native tree on alkaline soil, the beautiful bark and graceful branching of the Ironwood, or Hophornbeam, will quickly win you over. It is reliable on drier soils, and will take some shade from larger trees too. It grows in zone 3, and the clusters of inflated fruits do indeed look like the hops used for beer making.
Elm (Ulmus species): After the devastation by disease of these iconic trees in the middle of the last century, they are having a comeback, thanks to disease-resistant species and varieties. The graceful arching form of elm trees is complimented by their toughness and durability in difficult spots, including alkaline soil.
Junipers (Juniperus): Most pines and fir trees prefer acid soil, but Junipers are perfectly happy in it, as well as being drought resistant. The Eastern Red Cedar, Juniperus virginiana, is a native species big enough to qualify as a tree, and there are some great varieties available, with blue or green foliage, and often big crops of showy berries.
Arborvitae (Thuja): This is another group of conifer evergreens that have no problem growing in all but the harshest alkaline soils. One thing you will be able to have is wonderful hedges!
Next week, in Part 2 of this blog, we will look at some shrubs that are especially suitable for alkaline soils.
***If you want to check the availability of any of the plants mentioned here, go to our Home Page, click on the ‘Search’ button in the upper right, and type in your choice – both common names and botanical ones will work. If, sadly, you find the item sold out, click on the ‘notify me’ box beside the size you want, and you will get an email the moment that plant is available again – it’s easy.
