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Ask Dayle

10/31/2013 - West Side Leader
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By Dayle Davis

Shown is the area under a reader’s spruce tree where plants have not thrived.
Photo courtesy of Karen Calabrese
Q: This very old Spruce tree had been limbed up a few years ago and now weeds want to grow under it, and any hosta I put in does not thrive, and eventually dies. Supposedly it is not a good thing to add topsoil at the base of any tree that changes its planting depth. There is so much detritus under this tree from many years of its annual cycle, and nothing will grow in it. Can I rake this debris away and add new soil without damaging the tree? It is in my front yard and I want it to look nicer for me and my neighbors.

A: Three conditions need to be addressed when planting beneath established evergreen trees: acidic soil, dryness and shade.

  • Acidic soil: There is no need to rake away the organic detritus that has built up under the boughs of your lovely old evergreen tree. Decomposing fallen needles under any spruce tree will eventually acidify the soil under it, and there are many acid-loving perennial plants and groundcovers that would thrive in your soil. Thrive is a relative term, however, based upon the amount of attention you are prepared to devote to meeting the basic needs of the plants growing under the tree.
  • Dryness: Any mature spruce tree is a thirsty animal with roots that will soak up all available moisture, including the water that small plants underneath its canopy are trying to absorb. Thirsty roots make for very dry soil.
  • Shade: A mature evergreen has large needle-laden boughs that block the sunlight and create a very shaded atmosphere at the base of its trunk.

My guess is that the weeds growing under your tree are those that thrive in acidic dry soil.

Another guess is that your hosta (which prefer a soil more on the acidic side) failed to thrive and eventually died because of not enough moisture in the soil.

What to do? Well, weeds happen whether desirable plants are present or not, so you could simply clean up the space. Edge the tree bed nicely, pull the weeds, then scatter a weed seed sprout preventative. Add a nice layer of bark mulch and quickly pull new weeds as soon as they appear throughout the growing season.

If you prefer to plant, below is a partial list of acid-loving perennials that will tolerate life beneath your tree as long as their requirements for moisture are met.

Keep in mind that pine needles will always fall and can overwhelm small plants, so some raking and/or blowing of needles is required, especially while new plants become established. Try to choose plants with larger leaves that have a bit of strength to them, or ferns which tolerate needle litter well or shade-loving ornamental grasses with blade-like leaves that easily slip between the tines of a rake. Otherwise, a rake will make short work of any plant with delicate foliage.

If you plant the area, I suggest concentrating on the outer edge of the tree’s drip line, where the plants may find it easier to find a drink of water.

When planting perennials, first topdress the area with a thin, 1- to 2-inch layer of well-rotted compost. The compost will help your new plants by providing a few loamy areas to put down roots and become established. Plant the perennials and then add wood chip mulch to help keep moisture in.

To maintain any plant beneath your tree, a steady supply of moisture is essential. Check the moisture level of the soil frequently. Consider drip irrigation, which applies water exactly where your new plants will need it.

• Perennial plants for acidic soil include:

√ Hosta

√ Dryopteris erythrosora, aka autumn fern

√ Polystichum polyblepharum, aka tassel fern

√ Rhododendron

√ Hakonechloa macra ‘Aureola,’ aka Japanese forest grass

√ Ophiopogon planiscapus ‘Nigrescens,’ aka black mondo grass

√ Asarum caudatum, aka wild ginger

√ Dicentra Formosa, aka bleeding heart

√ Polystichum munitum, aka sword fern

√ Blechnum spicant, aka deer fern

√ Adiantum aleuticum, aka five finger fern

• Perennial groundcovers for acidic soil include:

√ Viola: Violets spread prolifically and will need to be thinned each year

 √ Convallaria majalis: Lily of the Valley, spreads well, needs to be thinned

√ Galium odoratum: Sweet woodruff spreads readily

√ Liriope spicata: Liriope can spread quickly

√ Vinca Major and Vinca Minor: These two species of vinca vine are often called periwinkle. They are a flat vine-like ground cover that can spread quickly. Each plant grows no more than a few inches tall but can reach as much as 3 to 4 feet wide, which makes for a great ground cover. Vinca major has larger leaves and flowers; it is faster growing and is a bit more aggressive. However, it is not as hardy or drought tolerant as vinca minor and may not survive a very cold winter.

For more horticultural information, call The Ohio State University Summit County Extension hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3, and request Fact Sheet HYG-1002-96, “Fertilizing Landscape Plants.”

Please note fact sheets are sent out free; there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at the public library.


Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and coursework in botany, geology and wildflowers. Davis is certified as a Master Gardener under The Ohio State University’s Horticultural Extension.

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