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:

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

Willows
-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)

Oak

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

Cypress


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, http://www.wrdist.com/root_control_product.html

(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.