Best maintenance practices

 

Competitive plant management

“native does not designate a condition that is original and authentic. Rather … the native is the creation of the colonial state: colonized, the native is pinned down, localized, thrown out of civilization as an outcast, confined to custom, and then defined as its product” (Mahmood Mamdani in Botanical decolonization: rethinking native plants¹)

Across literature, terminology around what is typically referred to as “invasive, non-native” plant species differs. In general, these competitive plants can be categorized as having a negative impact on ecological systems through rapid spread, resulting in economic cost of management and a decline in the health of localized biodiversity. The legacy of naming has been linked to anti-immigrant ‘nativism’ as suggested by social scientists and scholars since the 1990s and as such, we wish to challenge the use of the term ‘native’ and ‘non-native’ to ‘competitive plants’ for the purpose of the blog¹. We encourage you to read the book Dispersals by environmental historian Jessica Lee, who discusses with nuance the language and stories of plants and their entanglement with our human world.

Common terminology you’ll see includes:

Weed | Subjective terminology for a plant that is a perceived nuisance to the person or people managing/sharing space with the plant.

Alien species | Species that have become established in areas outside their natural range².

Invasive species | Alien species are capable of causing significant harm to our environment, the economy or to society².

Non-native plant | Species that have not existed historically in one area but have been introduced due to human activities³.

Native species |  “indigenous terrestrial and aquatic species that have evolved and occur naturally in a particular region, ecosystem, and habitat⁴.”

The Invasive Species Council of British Columbia is the governing body for competitive plants for our region. In the Lower Mainland, the Invasive Species Council of Metro Vancouver (ISCMV) further details the plants of particular importance to manage through manual or chemical intervention including:

  • Buddleja davidii – butterfly bush
  • Cirsium arvense – Canada thistle
  • Vinca minor – common periwinkle
  • Daphne laureola – daphne
  • Ilex aquifolium – English holly
  • Hedera helix – English ivy
  • Myriophyllum spicatum – Eurasian watermilfoil
  • garlic mustard
  • Heracleum mantegazzianum – giant hogweed
  • Ulex europaeus – gorse
  • Impatiens glandulifera – himalayan balsam
  • Rubus armeniacus – Himalayan blackberry
  • Polygonum spp – knotweed
  • Hieracium spp. – orange hawkweed
  • Myriophyllum aquaticum – parrot’s feather
  • police-man’s helmet
  • Lythrum salicaria – purple loosestrife
  • Cytisus scoparius) – wild chevril
  • Lamiastrum galeobdolon – lamium
  • Iris pseudacorus – yellow flag iris

Pest management

IPM | Integrated Pest Management is a decision making process to manage pests in an effective, ecological and environmental way⁵.

Local Pests

 This is just a select list of some of the introduced and natives pests that are affecting the plants and trees surrounding Vancouver. 

Emerald ash borer – An invasive beetle that has spread across North America through the movement of wood, such as firewood, woodchips and pallets. The Emerald ash borer causes damage to trees in the genus Fraxinus (Ash) by impeding the trees ability to receive nutrients⁶.

Western Hemlock Looper Moth –  A moth native to North America, that feeds heavily on the foliage of conifers trees causing defoliation. Outbreaks usually last one to three years⁷ . 

European chafer beetle – An invasive beetle which was introduced to British Columbia in 2011. The European chafer beetle feeds on the roots of turf grass, causing damage to many green spaces⁸. 

Mountain pine beetle – An insect native to Western North America. The range and population of the Mountain pine beetle is growing due to milder winters and warmer summers. Mountain pine beetle affect a wide range of pine trees, including lodgepole (Pinus contorta), ponderosa (Pinus ponderosa) and western white (Pinus monticola)⁹. 

Japanese beetle – An invasive beetle that has spread throughout North America, and was first found in British Columbia in 2017. Japanese beetles feed on over 300 species of plants, and pose a threat to the ecosystems and the agricultural industry¹⁰. 

Mulch

Mulching has well-researched benefits of conserving soil moisture, rebuilding soil nutrients, conserving moisture, controlling the temperature of soils, minimizing erosion loss, reducing the effects of pesticides, fertilizers, and heavy metals, reducing the growth of competitive weeds, and improvement of the microbial community by promoting the conditions to sustain symbiotic interactions¹¹.

Best practice is to provide newly planted trees and plants with mulch in the late spring after the ground has warmed up enough to support plant growth, in a 1-4 inch spread, with careful attention not to pack mulch directly at the base of the plant or tree¹². DO use mulch that is organic, in the form of leaves, compost, straw, or seasoned wood chips and AVOID limestone crushed rock or shells as they can alter the pH of the soil, as well as fresh wood chips in perennial gardens which can deplete the nitrogen content¹². Also stay away from plastic synthetic fabric, dyed mulch, and fine-textured mulch which can compact when wet.

Avoid mulch volcano's around trees shown in the photo above, where excess mulch was piled around the base of the tree stem which can lead to bark rot and decay, compromising the structural integrity of a tree¹³.

Watering

The most efficient method of watering will depend on the type of plants and location. As a general guideline, watering plants at the roots, deeply and less frequently will encourage deeper, more drought tolerant root growth¹⁴. Watering either in the early morning or evening will help avoid water evaporation from the sun and wind.

Pruning

These are just general guidelines for pruning, there are many different techniques for pruning depending on species, desired appearance, and health of the plant. 

Trees

Common terminology for pruning trees¹⁵

Primary leader | A dominant terminal bud on the central branch. If the primary leader is viable, they will suppress growth on terminal buds of lateral branches. 

Co-dominant leaders | If the dominant and lateral branch are roughly the same diameter, two leaders can emerge after the terminal leader is removed. Birch is a common tree sold with many multiple codominant leaders 

Branch collar | Trees add layers of wood covering the trunk of dominant branches, forming a small bulge. This makes the branch have a stronger attachment on the bottom of the branch, rather than on top.

Epicormic branches | Activated dormant buds that can form below the stress point. 

Suckers | Surface roots of some species have latent buds embedded that develop into branches. Suckers require constant pruning.

For pruning trees, a general rule, it’s best to prune before spring flush to increase growth and wound closure (ISA). 

Its important to avoid cutting a branch flush with the trunk of the tree, which would cut the branch collar. It's best to find the branch collar and cut a few inches above it¹².
Image credit: University of Florida

Reasons and techniques for pruning trees (ISA)

Cleaning

  • Removal of dead, dying, diseased and weakly attached branches

Raising

  • Removal of the lower branches to provide clearance for buildings, vehicles, pedestrians, and views

Reduction

  • Reducing the size of a tree, often for utility line clearance.
  • Best done by pruning back the leaders and branch terminals to secondary branches that are large enough to assume the terminal roles (at least one-third the diameter of the cut stem).
  • Helps maintain the form and structural integrity rather then topping the tree.

Reducing density

  • Thinning can increase wind or light penetration and to promote interior foliage development



1. Mastanak, Tomaz and Elyachar, Julia. Botanical decolonization: rethinking native plants. Environment and Planning D: Society and Space, volume 32, pages 363-380, 2014.
2. Environment and Climate Change Canada (ECCC). Alien and invasive alien species. Government of Canada, 2017.
3. Sotello, Gabriella. What is the Difference Between Native, Non-native, and Invasive Plants? National Auduban Society, 2022.
4. United States Forest Services. What Are Native Plant Materials? n.d.
5. Government of British Columbia. Integrated Pest Management. 2016.
6. Invasive Species Council of BC. Emerald ash borer. 2023.
7. Government of British Columbia. Western hemlock looper. 2024.
8. Invasive Species Council of BC. European chafer beetle. 2023.
9. Government of Canada. Mountain pine beetle. 2024.
10. Invasive Species Council of BC. Japanese beetle. 2023.
11. Iqbal, Rashid, et al. Potential agricultural and environmental benefits of mulches—a review. Bulletin of the National Research Centre volume 44, Article number: 75, 2022.
12. Reed, Sue. Energy-wise Landscape Design – A New Approach for your Home and Garden. pp. 305. 2010.
13. Cue, Kathleen. Mulch Volcanoes – A Harmful Practice for Trees. Nebraska Extension in Dodge County, 2024.
14. Capital Regional District. A Homeowner’s Guide to Outdoor Water Use. CRD Environmental Sustainability, n.d.
15. Urban, James. Up by Roots: Healthy Soil and Trees in the Built Environment. International Society for Arboriculture, 2008.