Gardening, for many folks, is a relaxing way to enjoy the outdoors and add beauty to their world with flowers or to benefit from freshly picked vegetables and fruit. A successful garden involves several important factors, including soil quality and its pH level. If you have high-alkaline soil, you may be wondering which plants can successfully grow in it.
Plants that grow in high alkaline soil must be able to tolerate and grow at a pH of 7.1 or greater. A variety of perennials, shrubs, trees, and vines – such as lilac, daphnes, and elms – have adapted to tolerate higher alkaline levels, but very few will thrive when the alkaline level is 8.5 pH or more.
Soil quality and pH vary in different parts of the country. What grows in one locale with acidic soil may not fare so well in alkaline soil. If you’ve got alkaline soil and want a successful garden, put down your trowel and keep reading to see what grows best in your dirt.
Plants that Grow in Alkaline Soil
If you’ve got alkaline soil, even high alkaline, you may despair that plant choices are limited. That is somewhat true but, take heart, there are options. You can also consider amending the soil to lower its alkalinity, which we’ll discuss later in this article.
For now, let’s talk about plants that will grow in alkaline soil. There are not too many that thrive in very high alkaline soil because it’s difficult for them to get enough iron. Most prefer the lower end of the alkaline range to reach their full potential.
What you can plant in your yard depends a lot on which Plant Hardiness Zone you’re in. For each category, we’ve provided you with a sampling of possibilities.
The list of annuals that tolerate alkaline soil is not as lengthy as the perennial list. Since annuals are short-lived, they really need ideal soil conditions to maximize their single growing season.
|Lantana||Buddleia (Butterfly Bush)||Bachelor Buttons|
|Shasta Daisy||Easter Lilies||Sweet Alyssum|
|Lenten Rose||Black-eyed Susans||Geranium|
Shrubs provide the backdrop to the rest of your garden. Alkaline soil is best suited for deciduous shrubs, which lose their leaves annually. Many of these are flowering plants, helping to add color to the garden.
|Red-tip Photina||Lilac||Oakleaf hydrangea|
Trees are not usually too happy in alkaline soil, particularly evergreen trees which need the iron found in more acidic soil. However, these varieties tend to fare well in alkaline soil:
- Common Beech
- Japanese Maple
- Little Gem Magnolia
- Horse Chestnut
- Ornamental Cherry
- English Dogwood
A few vines will grow in alkaline soil, but be aware that some grow aggressively and will need routine maintenance to stay under control:
- Boston Ivy
- Virginia Creeper
- Vinca Minor
The ideal pH for a vegetable garden is in the 6.0-7.0 range, with 6.5 being ideal. However, these vegetable plants usually can manage in alkaline soil:
- Pole Beans
Understanding Soil pH and its Effects on Plants
Soil is one of the key components of a successful garden. Think about it: Soil is the foundation of your garden. It holds your plants in place and provides them the nutrients needed to grow. Knowing and understanding your soil is the first step to a green and productive garden.
Remember back to high school biology when you learned about acidic or basic solutions? Alkaline is another name for the term “base.” And you probably learned that pH is a measure of the acidity or baseness of a solution.
Soil pH is a measure of the acidity or alkalinity of the soil. The pH measurement is on a 14-point scale, with the sweet spot being between 6.0 and 7.5.
|Soil Type||Soil pH||Nutrient Availability Issues (Less)||Nutrient Availability Issues (More)|
|Acidic||0.0 – 6.9||LESS nitrogen, phosphorus, potassium, calcium||MORE aluminum and manganese|
|Alkaline||7.1 – 14.0||LESS iron, manganese, copper, zinc||MORE potassium, sulfur, magnesium, phosphorus|
The pH is important because it determines which essential nutrients are available to your plants and how they will be exchanged from the soil to the roots.
Different plants prefer, and even require, a certain pH to thrive. Having extreme measurements on either end of the scale won’t kill your plants, but it will affect what you can grow successfully.
What is High Alkaline Soil?
According to the Oregon State Extension Office, areas with lots of rainfall (east of the Mississippi River and in the Pacific Northwest) typically have acidic soil. Rain leaches out nutrients like calcium and magnesium and leaves behind aluminum and iron.
In areas where there is less rainfall, such as west of the Mississippi River, the soil is more alkaline. The lack of rainfall keeps the soil more arid, allowing some nutrients to stay in place. But there is also less decomposing matter to add acidity to the soil.
In addition to moisture content, soil pH can be affected by its location and original materials. Soil that is formed from more basic (or alkaline) rocks will have a higher pH. Soil near a road or area covered by concrete contains more lime and has a higher pH, making it alkaline.
Soil is considered to be alkaline if its pH is greater than 7.1. Very high-alkaline soil occurs when the pH is 8.5 or greater.
Determining the pH of Your Soil
The only way to find out the pH of your garden soil is to test it. Soil testing kits (link to Amazon) are available online or from a local gardening store.
Each state also has a Cooperative Extension Service that often provides soil testing free of charge or for a nominal fee.
One thing to remember is that you will need to test your soil every 3-5 years as its composition and pH levels will change over time.
Amending Alkaline Soil
While you can find plants that will tolerate alkaline soil, most prefer to grow in the “sweet spot” of 6.0 to 7.0 pH, slightly acidic soil. Plants struggling to make it in alkaline soil will often show evidence of lacking the nutrients they need:
- Iron: Iron chlorosis is an iron deficiency that causes a yellowing of the leaves
- Zinc and copper: Plant growth will appear stunted and burnt as dying begins
- Manganese: Plants will show signs of gray stripes or spots on their leaves.
If you need to amend your soil to lower the pH level, there are several materials you can choose to do this:
- Add Elemental Sulphur: Lowers pH over time when mixed in with garden soil
- Add Aluminum Sulphate: Acts quickly as the aluminum produces acid immediately upon contact with the soil
- Add Organic Matter: This includes peat moss, composted wood chips, or sawdust
Amending the soil is not a “one and done” gardening task. Lowering the pH to a more neutral or slightly acidic level will last for a while, possibly several years, depending on other factors such as annual rainfall.
Spring comes around every year, and then it’s time to get some flowers and vegetables in the ground to enjoy later on. A good first step is to test your soil to know what you’re working with and amend it if necessary.
If you’ve got alkaline soil in your garden, hopefully, you’ve gleaned some great ideas for plants that will grow and produce in your outdoor space.