En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
Not Yet Rated

Wednesday - June 12, 2013

From: Lakeville, MN
Region: Midwest
Topic: Drought Tolerant, Shade Tolerant, Herbs/Forbs, Shrubs, Trees
Title: Perennial Suggestions for Under Ash Trees in Minnesota
Answered by: Anne Van Nest


With our house we have inherited 2 ash trees in our front yard with a large amount landscaping underneath. I'm replacing the landscaping but there are tree roots at the surface preventing me from being able to dig and plant new perennials. Our ground is very compacted and clay-like. Is it safe to cut the roots out or will this damage the trees? Is it a safe option to mound above the roots with black dirt and plant new landscaping? The trees are approximately 11 years old and I believe they were planted too close together - about 10-15 feet apart. Is it best to remove the trees and start over?


Your issues with growing plants under trees and dealing with the tree roots are a big challenge for many gardeners. Colorado State University Extension have put a very good article online about tree roots. It is by J.M. Sillick and W.R. Jacobi and is entitled “Healthy Roots and Healthy Trees.” Some of the key points are:
• Most tree roots are located in the top 6 to 24 inches of the soil and occupy an area two to four times the diameter of the tree crown. Roots grow where water, minerals and oxygen are found in the soil. Because the greatest supplies of these materials are usually located in the surface layer of soil, the largest concentration of feeder roots exists in this zone.
• Large roots and small feeder roots occupy a large area under ground. Typically, the root system of a tree extends outward past the dripline, two to four times the diameter of the average tree's crown.
• Roots obtain water, oxygen and minerals from soil. They do not grow toward anything or in any particular direction.
• Soil compaction, change in soil depth and improper watering can injure roots, increasing stress and susceptibility to disease and insects.
The Extension people say that changes in soil depth around trees can cause injury to root systems. The addition of only 4 to 6 inches of soil over a root zone drastically reduces the amount of oxygen and water available to the roots.  So cutting the roots out or adding additional soil on top of the roots is not a recommended solution.

Even though your trees are 10-15 feet apart, once they grow together they will focus their growth to the outward facing areas where the branches have the most sun exposure. More than likely they will fare just fine. If you are concerned, an arborist can give you a more detailed recommendation.

The best suggestion is to plant a low, native groundcover that tolerates dry shade and compacted soil under the trees or replace the old landscape plants with a mulch layer and create some new planting beds away from the ash trees where the roots will not interfere and there is more sunlight.  You should put your new planting beds two to four times the diameter of the mature ash crown.
The Ladybird Johnson Wildflower Center has a list of recommended native plants for your state in our plant database page. There are 173 plants to consider in the Minnesota Recommended list.

If you do decide to plant under the ash trees, Theresa Rooney of the University of Minnesota Master Gardeners has put together an information sheet with suggestions for planting in dry soil for shade or under trees. She gardens under a 100-year old elm tree and says that locations in dry shade are some of the most difficult to grow plants because of the competition for water, light and nutrients.

To compile a list of native plants for planting under the ash trees, go to our Native Plant Database. Under Combination Search, select the following categories: State – Minnesota, Habit – shrubs, and then search again for herbs (for herbaceous), Duration – perennial, Light Requirement – shade, and Soil Moisture - dry. You can further narrow down the list of potential plants by indicating whether you prefer a deciduous or evergreen plants, specific blooming times or blooming colors.

Some dry shade shrubs that grow in Minnesota that are in our native plant database include:
Amelanchier alnifolia (Saskatoon serviceberry)
Arctostaphylos uva-ursi (kinnikinnick)
Ceanothus americanus (New Jersey tea)
Diervilla lonicera (northern bush honeysuckle)
Elaeagnus commutata (silverberry)
Rhus aromatica (fragrant sumac)
Shepherdia canadensis (russet buffaloberry)
Symphoricarpos orbiculatus (coralberry)
Viburnum rafinesquianum (downy arrowwood)
And some native perennials for dry shade in Minnesota include:
Astragalus crassicarpus (groundplum milkvetch)
Geum canadense (white avens)
Lobelia spicata (palespike lobelia)
Maianthemum stellatum (starry false lily of the valley)
Mitchella repens (partridgeberry)
Polygonatum biflorum (smooth Solomon’s seal)
Pteridium aquilinum (western bracken fern)


From the Image Gallery

Saskatoon serviceberry
Amelanchier alnifolia

Arctostaphylos uva-ursi

New jersey tea
Ceanothus americanus

Northern bush honeysuckle
Diervilla lonicera

Elaeagnus commutata

Fragrant sumac
Rhus aromatica

Symphoricarpos orbiculatus

White avens
Geum canadense

Starry false lily of the valley
Maianthemum stellatum

Mitchella repens

Smooth solomon's seal
Polygonatum biflorum

Western bracken fern
Pteridium aquilinum

More Herbs/Forbs Questions

Correction of tree name from Bay Point CA
October 16, 2013 - The tree should of been Mulberry don't know how it was changed!! Tuesday - October 15, 2013 From: Bay Point, CA Region: California Topic: Non-Natives, Cacti and Succulents, Trees Title: Non-...
view the full question and answer

Deer resistant plants for Trinity, TX
March 23, 2013 - I need a list of deer resistant flowers, herbs and plants that would could be planted in Trinity, Texas.
view the full question and answer

Fragrant foundation plants for sunny, dry area in Illinois
August 26, 2009 - We need suggestions of what to plant on the south side of our house heave sun and rather dry soil. We just took out old dead bushes. Would prefer something that flowers and smells nice that would gr...
view the full question and answer

Insect infestation, identification and treatment
April 21, 2008 - help! I have an infestation of small flies in my flower/vegetable beds. They seem to be eating the leaves of just about everything. I've tried to find out exactly what they are, but haven't had any ...
view the full question and answer

Plants for pergola in Lubbock TX
May 29, 2013 - I need suggestions of plants, vines, bushes to plant in my backyard near my wooden pergola that will work well in full sun in Lubbock, TX. Ideally, I'd like some that attract hummingbirds and provide...
view the full question and answer

Smarty Plants's Facebook profile Support the Wildflower Center by Donating Online or Becoming a Member today.

Mr. Smarty Plants wants you to be his Facebook friend. Click the Facebook icon to add yourself to Mr. Smarty Plants list of friends.
© 2015 Lady Bird Johnson Wildflower Center