What can I plant under an established fir tree?
Common douglas fir, Pseudotsuga menziesii, is a deep-rooting species. However, as in many other tree species, its root structure varies according to the nature of the soil. In deep, well-drained soils, taproots may grow up to 50% of their final depth in 3 to 5 years. Plate-like root systems develop when it grows in shallow soils or with a high water table. Fine roots are concentrated in the upper 20 cm of soil.
As fir trees take up most of the moisture and nutrients where they are situated it can be difficult for other plants to grow beneath them. If you can find gaps between the support roots you can amend the soil and plant native species such as sword fern (Polystichum munitum). The Pacific Northwest Gardenerís Book of Lists is a great resource and suggests the following plants also grow in the shade under trees: Siberian bugloss (Brunnera macrophylla), Lily-of-the-valley (Convallaria majalis), Fringed bleeding heart (Dicentra eximia), Hellebore (Helleborus spp.), Plantain lily (Hosta spp.) and Lungwort (Pulmonaria spp.). Bulbs spring flowering bulbs such as camas, shooting stars, fawn lilies (Erythronium californicum) can also grow well under fir. Mulch in late winter and water regularly.
Sources:
McNeilan, R., McNeilan, J. (1997) The Pacific Northwest Gardenerís Book of Lists, Taylor Trade Publishing
https://www.for.gov.bc.ca/hfd/library/documents/treebook/TreeBook.pdf
