Planting Under Evergreens

OK, technically this is a designing and planting UNDER evergreens (not WITH evergreens) but let’s roll with it. “Why won’t anything grow under this spruce!” Try planting under a pine, fir, or any other large needled evergreen, and you get a universal refrain echoed by professionals and garden enthusiasts all over the country. This blog explores the reasons plants won’t grow under your conifers, and what you can do to create a beautiful landscape when planting under and around mature evergreens.

First we’ll explore the most popular assumption as to why nothing will grow: “The soil is too acidic (or toxic?)!”

Let’s put toxic to bed right now. It is flat out not true. A myth. Now many others believe conifers acidify the soil around them through needle drop to the point where no other plants will thrive. It is true that the soil around conifers is often acidic. As a general rule, conifers prefer more acidic soils, and if you see a large, healthy needled evergreen you can usually assume some level of soil acidity. It is also true that, over long periods of time, some species of conifers acidify the soil around them through needle drop especially if the pine needle duff is allowed to decompose and is not cleared out each spring.

Planting under evergreens bares all

A natural pine duff layer

But let’s take a moment to review the pH requirement of many evergreens in comparison to the pH requirements of most ornamental landscape plants. Although they can often withstand more acidic soil, the ideal pH for Norway spruce, Fraser fir, Canaan fir, Scotch pine, White pine, Douglas fir, Blue spruce, and Concolor fir is between 5.5 to 6.5. This jives fairly well with the average range of 5.8 to 7.0 for most ornamental landscape plants!

Here, just as in the rest of life, it is important to never assume. Always test your soil before pinning the blame on low pH! You can make some amendments to the soil to bring the pH up a little while still maintaining it in the acidic range that your evergreens will love.

Regardless of soil pH, there are likely three other tricky factors at play under your tree: Shade (possibly very deep shade), dry conditions, and nutrients. The dry conditions are due to two factors. First, the dense canopy creating the shade also prevents much water from reaching the ground directly under the tree. Second, up to 75% of feeder roots for the tree are in the top 12” of soil. These roots are competing intensely with any other plants for available moisture and nutrients.

So to counter these challenges, you must create the dreaded DRY SHADE GARDEN! Any internet search will reveal that dry shade garden plants are about as easy to find as the holy grail.

So before you charge ahead, ask yourself one more time: do you REALLY need to plant under that evergreen, or can you plant around it and neatly mulch the area directly under the tree? If you decide you really must plant, get ready to tackle the last hurdle: extensive surface roots!

The surface roots from your tree can make it very difficult to dig in new plants. Adding planting soil on top of tree roots can kill a tree, so the best bet is to buy the smallest plants available and dig them in individually around the roots. Apply 2” or so of mulch (never more than 4”, as deeper mulch could be detrimental to the tree), and water your new plants very well at least for the first growing season, or until it looks like they are holding their own. In drier climates of the country you can probably count on ALWAYS having to maintain irrigation under the evergreen tree to make sure even the dry shade plants thrive. It is a delicate balance, however, as overwatering in the shade and developing fungus and root rot issues is a common misstep.

Finally, this still does not tackle your final challenge of nutrient competition. A large, healthy evergreen is sucking up a significant amount of the nutrients in the soil. By committing to planting directly under the tree you are committing to a constant refresh of the plants every few years as they run low on nutrients and cannot compete with the large tree OR you are committing to a CONSISTENT regimen of soil amendments. Either way, these gardens will require serious nurturing.

The Plantium is a great resource to quickly spec dry shade plants for your project. Another way is to just head out to the woods and check out the natural understory in your area! Lastly, botanic gardens and the agricultural extension for your area are great sources for dry shade plant recommendations.

Conquering planting under evergreens

What success looks like!

Do you have something to add to the conversation?

Your email address will not be published. Required fields are marked *