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Portland Nursery

Under-Planting a Large Tree

Mature trees bring beauty and
a sense of history to our outdoor spaces.

under-planting-combo

All too often though, the dense canopies and aggressive root systems of these trees create daunting patches of dry, deep shade that defy even expert gardeners. But don’t despair! With a bit of research and
extra compost these barren areas can be transformed into another lush corner of the garden.

Featured Plants

three-plants

Sword Fern, Polystichum munitum — Commonly seen in redwood forests, this evergreen fern will reach 2-4 feet tall and wide at maturity. It’s leathery dark green leaves provide a sense of height and structure.

Epimedium — A shallow rooted ground cover that looks delicate but is tough as nails and highly adaptable. Heart shaped leaves are suspended by dark wiry stems.

Black Mondo Grass, Ophiopogon japonica “Nigra” — A low growing (6-8 inches tall) evergreen ground cover with striking black grass-like foliage. It’s a slow spreader but it dramatic color makes it a perfect partner for just about any plant.

Special Considerations:

Mature trees are water and nutrient hogs and the soil below them is often dry, depleted and chock-full of roots. These roots are often found in the first foot of soil, making it difficult for new plants to establish themselves. Heavily needled evergreen trees create an additional problem because their dense foliage blocks much needed winter moisture from reaching the ground directly below them. To contend with these trying conditions, look for plants that are shallow rooted and tolerant of drought and shade conditions. Believe it or not, there are plenty of beautiful plants that fit the bill!

Substitutes also exist, including Native Bleeding Heart (Dicentra formosa), Helleborus, Lenten Rose (Helleborus orientalis), Lilyturf (Liriope spicata), Lamium, Ajuga, Saxifraga stolonifera, Pachysandra terminalis, Salal (Gaultheria shallon), Wood Sorrel (Oxalis oregana) and Spring bulbs.

Epimedium

epimedium varieties

Image credits to Xera Plants

New growth on Epimedium may take on a mottled pink color in spring, which will turn to a lush green in summer and some varieties take on a lovely bronze hue in the fall. Fragile pale yellow, pink or red flowers emerge in April-May to hover above the foliage. Some species are evergreen, but even the deciduous species will hold their leaves late into the fall. Most varieties grow between 6-12 inches tall and spread slow-to-moderately fast.

Care & Maintenance

  • In the Pacific Northwest, the rainy season of winter and early spring is the best time to plant in dry shade situations. New starts will appreciate this extra moisture as they get established. But there’s a catch – to avoid soil compaction, wait for a dry spell so that the soil is not soggy when preparing the bed and planting.
  • Before planting, prepare the bed by adding a 3-4 inch layer of organic compost. We recommend reapplying compost or mulch every year to promote healthy soil and water control.
  • Dig your planting holes 1-2 feet away from the tree trunk, try to avoid unnecessary root disturbance by keeping the holes small.

Care & Maintenance

  • Though this option is not ideal, the top 3-4 inches of compost may be planted into directly if tree roots are too dense to plant in.
  • To help your plants establish the strong root systems they’ll need to survive drought conditions, give them 1 to 2 deep watering a week throughout the dryer months for the first two years. After this, the plants should only need occasional watering during the hot months.

Plant Spacing/Repetition
Addition of Plants

  • 11 – 16 square feet
  • Polystichum: 3 feet apart
  • Epimedium: 1-3 feet apart, ranges depending on variety
  • Ophiopogon: 8 inches apart