Plants for Under a Douglas Fir

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Q: Could you please give me advice on what to plant that is low maintenance and not invasive under a large, well-established fir tree that has a spread of over five feet. There is a fence corner under the tree so I am looking for plants from four feet tall starting at fence and decreasing in size to the drip edge of the tree at approximately 25 feet from the butt of tree. This area does not receive a lot of water as we’re trying to conserve water. I live in Nanaimo, B.C.

This is a pretty difficult situation for a plant as the roots of the big Douglas fir will take all of the moisture and nutrients out of the ground.

Where I used to work (at the Miller Garden), we planted under large conifers, but we added about 2 centimetres (5 in.) of mulch each February, which built the soil up. In addition, we watered regularly.

Your first step could be to determine what you might have in the way of planting space. In the fall, dig a bit under the fir to determine where you might be able to create a planting hole. You’ll find large support roots and probably some gaps between them where you can excavate a planting hole to amend with good soil and compost. Don’t use peat as it tends not to re-wet once it gets dry.

Draw the shapes and placement of these holes on a piece of graph paper to determine the sizes of the plants you will need to fill in under the fir.

I would stick with evergreen shrubs for this area, as many have thick waxy leaves that make them very drought tolerant. All do well in dry shade as long as you keep them watered regularly for the first two seasons so they have a chance to develop deep, extensive root systems.

In addition, try native sword ferns (Polystichum munitum), spurge (Euphorbia amygdaloides var. robbiae) and hellebores for a change in texture. Here are some suggested shrubs:

  • Fatshedera lizei and ‘Variegata’ (fatshedera) this sprawling shrub can be left to its own devices, reaching 2 feet high and 10 feet wide, or it can be trained on a trellis or fence to make a screen
  • Ilex crenata ‘Convexa’ (convex-leaf Japanese holly) grows to 6 ft high and wide, can be pruned to almost any shape
  • Ilex crenata ‘Mariesii’ (columnar Japanese holly) a narrow accent plant to 3 feet high and only 1 foot wide
  • Lonicera pileata (box-leaf honeysuckle) this spreader will get to 3 feet high and 5 feet wide
  • Mahonia nervosa (cascade Oregon grape) native plant that grows to 2 feet high by 4 feet wide
  • Podocarpus nivalis (alpine totara) a conifer that grows to 3 feet high by 6 feet wide
  • Sarcococca confusa and S. hookeriana var. hookeriana (sweet box) both reach 3 feet by 4 feet
  • Sarcococca hookeriana var. humilis (dwarf sweet box) reaches 1 foot tall by 3 feet wide
  • Taxus baccata ‘Repandens’ (spreading English yew) conifer that grows to 3 feet tall and spreads to 6 feet wide

One last tip: I’ve also been experimenting and had good luck with a horticultural wetting agent. Wetting agents break the surface tension on the soil, so that the water can percolate down into the root zone. I’ve used one (easy to spray on with one of those dial-type hose-end sprayers) on a bed with many perennials and shrubs, and it has worked well. It lasts about six weeks and is not expensive. Now the water soaks in rather than running off my beds, which are also under tree roots.