Any advice on tree root invasion

laraine47July 7, 2010

I have a flower bed along a portion of our deck that is 6 ft 9 in. in length and 30 in. wide that is separated by a 3 ft wide interlock pathway with a wider garden on the other side that is home to an Ivory Silk Tree Lilac. The interlock path and gardens have been down now for 21 years along with the tree. I am having problems with the roots from the tree invading the flower bed on the other side of the path. I had to remove everything from the bed this June for a contractor who was demolishing our old cedar deck and replacing it with Ipe. When I dug up my hostas etc. which were not growing well I noticed the thick mat of tree roots and after I potted up my hostas I dug down 2 feet and filled one third of a leaf waste bag with tree roots. That is a lot of roots for such a small flower bed!I did the same process only 2 years ago and ammended the soil with compost and manure, but it seems that only helped the tree and not the hostas. Other than that, it is the perfect spot for my hostas as it is shaded by the tree and my question is....can I plant my hostas in plastic pots large enough for the hosta roots to expand but at the same time hopefully keeping out the tree roots? Or do I have to totally dig up the bed every year to get them out? I do not know how other people can successfully grow any hostas within the vicinity of a tree, and as far as trees go this one is considered small. HELP!!!!

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I have two very large Silver Maples that have a million and one surface roots that occupy the top 16" of top soil. I started growing hostas here 10 years ago and many times have had to adjust where I plant a new hosta to fit between the larger roots. The thin roots from the tree do absorb a great deal of moisture and make it very difficult to plant or dig anything out. It takes me 10 times the normal amount of time to plant anything and must be done with a hand trowel, pruners and an axe. It is very frustrating to deal with but it hasn't kept my hostas from doing well. I sometimes come across a hosta that does not like the tree roots but not very often. I seem to have a problem with heucheras not liking it here.

I don't bother to put anything in pots to bury as the roots are just a nuisance to me and not to my hostas.

    Bookmark   July 7, 2010 at 12:16PM
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dbowemd(z5 OH)

I have done pots in the ground and I have even done a double pot in the ground, so that the pot can be easily lifted out or spun to cut the tree roots... they do grow into the pots. It works well.
There is a bag made for this too, which you can get from wildrose distributing. It is an inverted tree bag which stops tree roots from penetrating, which were initially made for puting trees in to be sold. They keep tree roots out with the same chemical treatment.


    Bookmark   July 7, 2010 at 12:40PM
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Thank you Dave for the timely advice. Using plastic pots was the only thing I could think of..I did not know of wildrose distributing and their root control bags. They are the perfect answer and are cheaper than buying large plastic pots for my stained glass hosta and fire and ice. Will also be able to use them for the hostas I have on the other side under the drip edge of the tree. They were huge once and are also getting smothered and decreasing in size each year. I expected that to happen there, but not on the other side of the interlock that was excavated quite deep down 21 years ago. The temperatures are in the 90's all this week, we are dying here in eastern Canada and it extends all the way to Washington DC. That is why I am on the computer and not out gardening.

    Bookmark   July 7, 2010 at 2:15PM
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I have been using the bags from Wild Rose for 3 years now with great results. Here are some pics. All of these are growing in the root control bags under numerous maples.

I have had maple roots get in the bag, so make sure and leave a lip about one inch above the soil level. And don't forget to turn the bag inside out.

    Bookmark   July 7, 2010 at 6:51PM
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I just bought some "spin-out" bags made by Texel (Tex-r Agroliner) from Acme-Mackenzie Nursery Supply. I e-mailed Matt Rocky ( for pricing. I found the prices on their bags and the shipping very reasonable after some shopping around. I bought the 7 gallons (13" in diameter x 11 3/4" tall) and the 15 gallons (17" in diameter x 15 1/2" tall) bags. The 15 gallons bags are alitte tall so I cut 2"-3" off and turned down an inch or 2.

This is my first experiance with the bags, so I'll see how they pan out.

I too was having problems roots from a soft maple tree.


    Bookmark   July 7, 2010 at 11:17PM
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I grow hostas in the roots of mature maple and oak trees. My husband dug the holes with a pickaxe and I planted in pure compost. I topdress with compost occasionally and fertilize every spring with 5-10-10. I am careful about watering this bed on a regular basis because of the extra-dry conditions.

This garden bed is about 20 years old and has done beautifully. Companion plants that have done well are variegated Japanese Solomon's seal, carex, epimediums, our native Geranium maculatum, and silveredge pachysandra.

No doubt the plants would be even larger and lusher without the tree root competition but it looks great.

    Bookmark   July 9, 2010 at 10:13AM
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donrawson(Z 5)

Here are my notes from a PowerPoint presentation I gave this spring titled "You Can Have a Tree-mendous Garden!" There's much helpful information here on trees in general as well as twenty tips for dealing with root competition. Sorry, there's probably not enough room on this posting to include all of the pics from the PowerPoint. (If anyone wants a printed copy of the notes, please send me an email.)

You Can Have a Tree-mendous Garden!

Trees are major competitors for nutrients and water. If you're striving to grow huge, luscious hostas, you'll have to control root competition.

Getting to the root of the problem...

Problem: Roots

Large roots are called structural, or support, roots. Their main function is to anchor the tree.

Small roots are called absorbing, or feeder, roots. Their main function is to feed the tree.

Horizontal roots are called lateral roots.

Vertical roots are called sinker roots.

Tap roots- a central, vertical root that grows straight down beneath the trunk.

Root collar- the swelled up area at the base of the trunk.

Key Points

►Roots of trees grown in the open often extend two to three times the radius of the crown. The extent and direction of root growth is more a function of environment than genetics.

►Roots grow where moisture and oxygen are available. Most absorbing roots are found in the upper 12 inches of soil. In fact, 90% of the fine roots that absorb water and minerals are in the upper few inches of soil. Roots require space, air, and water. Roots grow best where these requirements are met, which is usually very near the soil surface.

Problem: Soil

The soil may be nutrient deficient.
The soil may be compacted.
The soil may be impenetrable.
The soil may be shallow.

Trees compete for water and nutrients. Trees are like giant sponges, wicking up an enormous amount of water.

A dry, shady area with low nutrient content and compacted soil is great for a moss garden, but hostas (just like grass) may need to fight hard to survive.

A shallow root system is likely where there is shallow topsoil, or rock or compacted subsoil.

Erosion over a period of time can cause surface roots to become exposed, particularly with trees on a slope or in an area that gets flooded.

Problem: Shade

While all trees provide some shade, certain trees create dense shade.

Hostas are shade tolerant, NOT shade-loving. They need sunlight to grow!

20 Tips for a Tree-mendous Garden

Although there are a variety of techniques to deal with the problem, the method(s) you choose to employ is determined by the amount of effort and money you're willing to expend. But if you choose to ignore it, your hostas will likely continue to decline and may eventually die out.

Tip #1 Choose your enemies.

Tree selection- Choose trees that have deep root systems. This may require tree replacement with varieties that have a deeper root system and a more open canopy.

Note: Shallow roots vs. deep root systems is somewhat of a misnomer, since nearly all trees will have 95% of their roots in the top 12-18" of soil. But some trees are known to have more fibrous root systems than others and make it nearly impossible to garden under.

Shallow and fine/dense roots system:

-all varieties including Japanese maple
-incredibly aggressive root system; will quickly grow into fresh mulch or imported top soil
-form a dense crown

-suck up a lot of water
-fast growing, aggressive root systems
-dirty tree which sheds lots of small branches

Aspen, poplars
-aggressive, fast-growing, spreading root systems; a weak tree

Beech, Birch, Honeylocust, Apple, Pear, Elm, Sweetgum, Magnolia, Mulberry

Deep root systems:

Nut trees- Hickory, Butternut (Black Walnut has tap root to China, but)


Ash- but many fine, dense roots make it unsuitable; also emerald ash borer


Dirty Trees:

Willow, Birch, Elm, flowering trees- limbs, small branches, flower petals, and seed pods that fall onto hostas and flowers

Tip #2 Choose vigorous hostas/plants.

Plant selection- Choose plants that thrive in the conditions where you want to plant them.

Hostas- Choose the most vigorous ones to plant directly under trees. While most are good growers, those with a lot of white are less vigorous and need more light.

Maples are super competitorsand grass is the most invasive weed in the worldit will grow in cracks in the pavement...and if a given tree can defeat it, as we all know it can, then understand that only something as vigorous must be planted under them!

Ferns- Dryopteris, NOT Ostrich ferns
Groundcovers- ivy, myrtle, pachysandra (the big 3)
Lily-of-the-Valley, Virginia creeper, lamium, lamiastrum, ajuga, epimedium
NOT- poison ivy, kudsu, chameleon plant (houttuynia cordata), crown vetch

Tip #3 Improve your soil.

The soil under trees is often nutrient deficient, compacted, and impenetrable for hosta roots. Compaction is also a problem for tree roots, reducing oxygen availability and causing the accumulation of carbon dioxide. Compaction reduces water infiltration and the absorption of minerals. An ideal soil for tree root growth is about 50 percent pore space.

In barren soil, there will be no humus added each year from the previous year, particularly if the leaves are raked up each fall. Improve the existing soil by adding compost, etc.

Tip #4 Add good topsoil around your trees.

Add 6-8" compost or amended soil. Caution: Dont put too much additional soil or mulch around trees that can suffocate roots which need oxygen. Especially important for trees with shallow root systems. Smothering tree roots by adding soil or raising the grade could even kill a sensitive, mature tree. Even if the grade change is not in the immediate vicinity of the root zone, the water table or drainage pattern could be affected, which can adversely impact trees.

Dont do spot dressing- Dont dig a hole for the hosta and then dump in good topsoil. The tree roots will head straight toward the invader. EVERY hole you dig for a plant into which you put improved soil will be infilled with new feeder roots from the tree a lot faster than the plant can get established. Amend the soil over a wide area.

Tip #5 Raised beds can be attractive.

Border the bed with pavers, landscaping timbers, railroad ties, etc.

Tips: Install landscape fabric before adding new soil. Stay 2 or 3 ft. away from trunk to avoid suffocation and collar rot diseases. Also, you dont want water to puddle around a tree trunk. Avoid thick layers of mulch around the base of the tree (often called "volcano mulching"), as far too often seen in landscapes. Two or three inches of mulch is the appropriate amount. Later applications to "refresh" the mulch should not increase the depth. Avoid organic material that can mat down and create a hydrophobic layer. Add soil gradually over a period of a few years.

Tip #6 Fertilize properly.

Fertilize the hostas under or near (large) trees more frequently. Dont spot fertilize. Always broadcast fertilizer under a forest canopy.

Tip # 7 Water, water, water!!!

Water requirements- the tree needs water and your hostas need water (competition)

How much water does a large tree use per day??? A large oak tree can draw up to 50 or more gallons of water per day. Some trees use 15 gallons of water per hour on a hot day, and some can draw as much as 150-200 gallons of water on a hot day. Times that by how many trees you have!

The amount of water needed by trees varies with the species, the size of the plant, the air temperature, humidity, light levels, soil type, and wind movement over the leaves. The same is true with flowers and perennials.

►High Demand- Elm, Oak, Poplar, Willow, Silver Maple, Manitoba Maple

►Moderate Demand- Cherry, Ash, Hawthorn, Hornbeam, other Maples (Sugar, Red), Mountain Ash

►Low Demand- Beech, Birch, Cedar, Fir, Mulberry, Pine, Spruce

What happens when trees and other plants become water deficient??? Over an extended period (a drought), plants respond by wilting, yellowing of leaves, developing modified leaves, dropping leaves, increasing the production of absorbing roots, slowing growth,...and eventually, death!

Water hostas which are under or near (large) trees more frequently. An underground sprinkler system will prove helpful in growing luscious hostas under trees, or at least irrigating during dry times. Tips: Dont spot irrigate, except for new plants. Always broadcast water under a forest canopy. Mulch around your hostas to conserve water.

Soil types- clay vs. sand. Because clay soils have a much slower infiltration rate than sandy soils, water needs to be applied slowly over long periods of time. At the same time, clay soils have a greater water-holding capacity than sandy soils.

Trees, plants and hostas in "heat islands", such as along driveways and parking lots, are particularly prone to water stress.

Tip #8 Get more light.

Thin the crown to allow more sunlight and increase light penetration. Shade increases significantly as a forest canopy matures, and sometimes we are unaware of how shady our gardens have become. Some trees have very dense crowns- maples, etc.

Thin out and prune off lower branches. Deadwooding- the removal of dead and dying limbs from a tree. Pruning- follow guidelines. The time and method of pruning is different for different trees. For example, prune maples and birches in the fall. Pruning can improve a trees structure or health. Flowering and new growth can be prevented or enhanced.

Tip #9 Dont plant babies.

Plant mature hostas, not small plants which have not yet developed enough foliage to survive and without extensive root systems. It is NOT going to be a plant and forget situationat least until the intruder achieves some level of establishment. In other words, you cant just slap a young plant in here and there, as compared to inserting a mature plant which can fend for itself, because the tree might win. Getting the invader ESTABLISHED is imperative, for it to try to compete on a successful basis.

Tip #10 Spade around your hostas.

Use a sharp spade to go around your hostas, shearing off any encroaching tree roots.

Can you identify the proper garden spade for the job? Tips: Use a square-bottom spade that has been sharpened to a razor edge using a file. Its easier to do with a pair of hard-soled work boots on, and after a long drenching rain. Do it a few times throughout the summer. Dont allow the tree roots to get too big.

Tip # 11 Root prune around the tree.

Go around the tree (2 or 3 ft. away from trunk) with a sharp spade to cut off surface roots. Do a couple times every year before roots have a chance to get too large. Or use a trencher. Caution: It may slow the growth of the tree.

Tip #12 Selective root pruning.

Cut off large roots which are directed toward your flower bed. Use Round-Up to prevent suckers from shooting up.

Tip #13 Dont neglect fall clean-up.

Vacuum or rake up leaves in the fall, especially with oaks (acidic). Broadleaf trees with large leaves will add a thick layer to the ground (voles, slugs).

Tip #14 Rotational farming.

Lift out the hostas, rotor till, add compost to improve the soil, open up the canopy above, and deploy soaker/drip hoses and replant. Tip: Do a different flower bed each year.

Tip #15 Plant your hostas in containers above the ground.

Plant hostas in flower pots, half whiskey barrels, etc. Advantages: You can move hostas around for variation and as size matures. Tips: pots should have drainage holes or tip on side for winter.

Tip #16 Plant hostas in containers in the ground.

Tips: Wrap landscape fabric on outside, or rotate the pot 90% two or three times throughout the summer. It may be very difficult digging a hole big and deep enough to bury a bucket in a root bound area. Water the area well the day before, and use a very sharp spade.

Tip #17 Buckets, barrels, and bathtubs.

Nursery pots and other containers such as large waste baskets, plastic drums cut in half, or even an old bathtub to plant large hostas. 5 gal. buckets which can be obtained from a fast food restaurant are suitable. You may also get them from painters and dry wallers.

Spray the top couple of inches if you dont want white rings scattered throughout your garden. Drill four small holes, about 3 or 4 inches up from the bottom, to make a constant water reservoir.

You can use two buckets to prevent tree roots from growing through the holes. Put one inside the other, but so the holes dont line up. Bury them in the ground and put your plant in.

Tip #18 Spin-out bags and fabric.

Tex-R Agroliner Spin Out® bags, available from Rose Distributing,

(10) 5 gal. $20.95, (5) 10 gal. $18.95

Tip #19 Install a root barrier around the tree.

Trench in a root barrier around the tree to restrict the roots from entering your flower bed. May limit/restrict the growth of the tree or cause girdling.

Tip #20 Install a root-proof liner under your flower bed.

A root-proof liner acts as a continuous barrier to prevent trees roots from encroaching.

-more work for flower beds that are already in place
-additional benefits: restricts ground moles; constant water reservoir
-a variety of materials may be suitable as a liner, depending on affordability: an old swimming pool liner; heavy plastic; landscape fabric (available in various sizes and thicknesses); poly tarps (last much longer in the ground because no UV rays); black rubber pond liner, or roofing material.

Dig out the topsoil where your new flower bed will be, to the desired depth. Rake the bottom of the hole flat and smooth. Install the liner.

The best material for a root-proof liner is black synthetic rubber which can be purchased from a water garden supplier or from a roofing supplier because the same material is used on flat roofs. It will last a very long time and the seams can be glued so there's no chance for roots to get through.

Regardless of the material you choose, proper installation of the liner is essential. Any breech- the slightest tear or hole- will seriously compromise its integrity. Seams must be impervious. The liner must come all the way up out of the ground, and can be fastened to a strip of lawn edging or landscape timber if desired. Be careful not to puncture the liner with a shovel or garden stake once it's installed.

Besides preventing root competition, a liner has additional benefits. A liner keeps out ground moles which otherwise would be tunneling through your flowers. And if the liner is leak proof, it can serve as a constant water reservoir, reducing the frequency and expense of regular irrigation.

If all else fails, eliminate your trees.

Trees make great firewood! Plant your hostas under a pergola or shade cloth.

    Bookmark   July 9, 2010 at 9:32PM
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Steve Massachusetts Zone 5b

I have a good sized Norway Maple in front of my house that I don't want to cut down. It provides good shade on the south facing side of my house and it would take too long and be too expensive to replace it.
Here's the maple in question. I took off some lower branches to allow for more sun.

I decided to plant some Hostas beneath it in Spin Out bags. These fabric containers can be purchased from Wild Rose Distributing. Their advert is on the Hosta Library main page. When you get these bags you turn them inside out. The black side is supposed to prevent competing roots from invading the space of your plant. The size I bought was 12"x12" square and about 16" deep. Here's a bag in the hole. It's supposed to remain an inch above the soil surface.

The planting area not only has root competition from the Maple, there previously was a Tree of Heaven (ailanthus altisima) in this area. This is an invasive, non-native devil plant that I have been digging out spraying with roundup for the last two years. Here's a pic of the root competition in the plant hole.

I chose a mature hosta for this planting. It's a plant I haven't IDed yet. Last year it was scorched badly in the summer and I couldn't recognize it. But it's a huge plant. I had to divide it in half to fit it in the bag and it probably still has 30-40 eyes.
Here it is planted in the bag.

I added a bag of composted cow manure to the soil I used to fill the bag. You can see that when you fill it with soil the bag tends to assume a round shape more conducive to planting. This is a good spot for this Hosta as it will get morning sun, but protection from mid day and afternoon sun. I'm hopeful that the spin out bag will give it the root protection that it needs to thrive. I'll update it in the later spring when I can better identify the plant.


    Bookmark   April 21, 2011 at 4:12PM
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Quite honestly, I have been reluctant to admit that I am growing hostas under maples. I worried that Hosta Welfare people would take them away from me and put them in foster care. I am ordering some bags ASAP.

Does anyone have an idea what size bag would work for a large hosta like Royal Standard?


    Bookmark   April 21, 2011 at 8:39PM
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squirejohn zone4 VT


It will be interesting to see how your experiment with Spin Out Bags goes. I was thinking of trying them last year but didn't think they were large enough. The largest size advertised was 11 X 11 X 16" and Grenfell states"...hosta roots spread out below ground to the edge of the leaf mound or beyond..." and large hostas such as 'sieboldiana' can be 6-8' across and the planting hole should also be 6-8'. Since most hostas have a leaf spread of greater than 11" I assumed the Spin Out bags were too small and wound up cutting down a bunch of trees. I have another small area loaded with American beech roots that I might try Spin Out Bags based on your results.

    Bookmark   April 22, 2011 at 6:41AM
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Steve Massachusetts Zone 5b


That's a good point. Hosta root systems seem much wider than they are deep. You can see from the pic above that this division takes up most of this bag, and that was after I divided it in half. This is a medium to large sized hosta and based on what I saw last year it should be about 30 inches in diameter at full maturity. It may be that it outgrows this bag, but if that happens then I feel good about its chances of fighting off the maple roots on its own. I don't know about you, but I don't dig planting holes 6-8'! Next I will try a less mature hosta under this same tree.

BTW, you can buy the spin out fabric on its own. Theoretically you could make a bag as large as you like.


    Bookmark   April 22, 2011 at 8:09AM
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ken_adrian Adrian MI cold Z5

boy steve... wish you would have started your own thread ...

anyway.. that nubbin you left on the maple ... how far does it project from the trunk .. looks a bit long to me...

otherwise .. God's work ... keep it up


    Bookmark   April 22, 2011 at 8:15AM
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Steve Massachusetts Zone 5b

Thanks, Ken. That nub is about 2 inches long. Should I cut it closer to the trunk? I didn't want to get too close.

As I think about this more, it occurs to me that I have a little more than a cubic foot to deal with, and I can make the bag fit the shape of the plant hole. So if I dig a hole 10 inches deep, I can get a planting hole more than 15 inches in diameter. I think I'll give that a shot next time.


    Bookmark   April 22, 2011 at 9:18AM
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I wrote what I did at:

Tree roots in vegetable garden


This post was edited by jyn510 on Sun, May 11, 14 at 2:46

    Bookmark   May 11, 2014 at 2:43AM
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