As one of the most popular perennials around, hostas are a landscaping staple. They are hardy and shade-tolerant, a combination that makes them perfect for filling in practically any outdoor area in need of colorful foliage. As forgiving as they are to care for, does the type of soil matter? Specifically, do hostas like alkaline soil?
The ideal pH range for hostas is slightly acidic (6.5) to neutral (7.0) or even slightly alkaline. Too much alkalinity in the soil, however, can lead to a lot of problems for hostas, such as poor extraction of nutrients which can lead to chlorosis (yellowing of the leaves) and other conditions.
When it comes to establishing and maintaining a thriving community of plants in your garden or backyard, the importance of having not just good quality, but the right type of soil, cannot be overstated. This is true for hostas, which do better in soil with a pH that is slightly acidic to neutral. Keep reading to learn why this is and what to do if your soil is too alkaline.
Do hostas grow in alkaline soil?
Like many plants, hostas prefer soil that is slightly acidic to neutral, which translates to pH levels ranging from 6.5 to 7.0.
While hostas can tolerate slightly alkaline soil, possibly even up to a pH of 7.5, going beyond that would push the outer limit of their ideal soil pH and could open the door to a host of harmful conditions, some with potentially deadly results (more on this later).
In addition to proper soil pH, hostas do best in partial shade with limited sun and soil that provides good drainage and plentiful nutrients. As those who are familiar with hostas can surely attest, once they are established, these perennials can thrive in less-than-ideal conditions (including drought) and spread their brilliantly-colored foliage over surprisingly large areas. They can also live for a number of years.
Why isn’t alkaline soil good for hostas?
Although hostas are a fairly rugged plant that can tolerate a variety of growing conditions (depending on the type, hostas can grow in USDA hardiness zones 3 through 9, which pretty much covers the entire continental US), when it comes to soil pH, they are quite particular and do not like soil that is too alkaline, meaning a pH level exceeding 7.5.
Soil that is too alkaline can be harmful to hostas in a number of ways.
Alkaline soil is deficient in certain vital plant nutrients, namely:
The roots of hostas cannot properly absorb nutrients from the soil largely because they have been rendered insoluble (i.e., the nutrients cannot be dissolved in water) by the high alkalinity.
Alkalinity in the soil can cause new leaves to wilt and stunt their growth. Hostas leaves will exhibit brown spots and areas of dead cells (including the tips of new leaves).
A particularly noteworthy consequence of alkaline soil is the unavailability of iron to hostas, either due to this vital nutrient being rendered insoluble or because the alkalinity has made it non-existent by being precipitated out of the soil.
Either way, iron deficiency is a leading cause of a condition known as iron chlorosis which is marked by a dramatic yellowing of the leaves of a hosta plant with dark green veining throughout. When a hosta is afflicted by iron chlorosis, its foliage has a severe deficiency of chlorophyll, the pigment that not only gives its leaves their familiar green color but more importantly, allows photosynthesis to occur.
Hostas that are affected by iron chlorosis will be less hardy and disease-resistant due to their diminished capacity to produce sugar, they will have stunted growth with poor fruiting, and in severe cases, whole sections or even the entire plant can die off.
How do I test the alkalinity of my soil?
While there are certain telltale signs that your soil is alkaline for your hostas and other plants, the best way to know for sure is to test the pH of your soil.
There are two approaches for testing your soil for alkalinity, using a more technical, laboratory-type setup or going the simpler DIY route:
The technical method involves testing equipment like a pH meter, a pH electrode (to measure the presence of hydrogen), a temperature probe, test beakers, and buffer solutions;
The DIY method is a simpler process requiring a pH tester (with a built-in temperature probe) and buffer solutions for calibration;
For recreational gardening needs, there are also pH test kits which typically involve the use of test strips that indicate an approximate pH value by turning a certain color.
How can I make the soil less alkaline?
If you have verified that your soil is too alkaline for hostas (or many other plants for that matter), fear not, for all is not lost. There are actions you can take to amend your soil to reduce the pH and reverse the alkalinity enough for hostas to thrive in your garden.
Here are a few options to consider if you need to decrease the alkalinity of your soil:
Adding elemental sulfur to alkaline soil can reduce the pH (it is recommended not to add more than 8 pounds of this additive per 1,000 square feet of soil to avoid harming established plants);
Another strategy for reducing alkalinity in your soil is to add organic material to the soil such as peat moss;
For soil that is sodic (having excessive amounts of exchangeable sodium), it may be necessary to amend the soil with gypsum or calcium sulfate in order to reduce the alkalinity (but it may be necessary to repeat this process for several years).
By reducing the alkalinity of your soil to a neutral or slightly acidic level, you can create a growing environment that is more hospitable for your hostas to thrive.
There are dozens of varieties of hostas and with their brilliant foliage, they are among the most popular types of plants for landscaping and gardens everywhere. While they are among the hardiest perennials and generally easy to maintain, hostas do require quality soil that drains well and perhaps most importantly, is slightly acidic or neutral.