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Pine bark fines

Also known as Composted pine bark, Bark fines, Soil conditioner

Growing mediumDepends
Composted bark Photo: Nesnad · CC BY 4.0

In short

Pine bark fines are small particles of pine bark, often aged or composted, used as a main ingredient of nursery and potting mixes. They drain well, resist compaction and are a common partial replacement for peat.

How it looks

Brown to dark brown woody particles ranging from fine dust to small chips. For nursery substrates, the University of Kentucky suggests bark ground through a 2–2.5 cm screen, with about 25–33% of particles finer than 0.5 mm.

Signs

Uncomposted bark can cause nitrogen deficiency (yellowing) as it decays. Fresh bark is more water-repellent than aged bark. Too many fines reduce air space; aging shifts particles toward the fine end.

What favours it

Fresh pine bark has a pH of about 4.0–5.0; the target for many woody ornamentals is 5.5–6.2, reached with dolomitic lime. Bark particles can have up to 43% internal porosity, and pine bark holds more plant-available water than peat despite lower total water holding.

Prevention

  • Choose aged or composted bark, which has better particle size and less nitrogen tie-up.
  • Add lime or choose a limed mix for plants that do not like acidic conditions.
  • Feed plants in fresh bark with extra nitrogen.
  • Moisten dry bark before potting.

Treatment

Start with the first step and move down only if the problem persists.

  1. If plants yellow in fresh bark, apply a nitrogen-containing fertiliser; follow the product label.

Pros and cons

Pros

  • A common peat alternative in bagged composts.
  • Stable, porous structure adds air to mixes.
  • Composted bark has higher cation-exchange capacity than raw bark.
  • Holds more available water than peat.

Cons

  • Fresh bark ties up nitrogen as it decays.
  • Acidic, so usually needs lime.
  • Quality and particle size vary between suppliers.
  • Fresh bark repels water at first.

Look-alikes

Orchid bark
Orchid bark is large, uniform chips; fines are much smaller particles and dust.
Compost
Compost is darker, crumbly and has no woody chips.

Typical uses

Nursery shrubs and trees in containers, general potting mixes (for example the Clemson and Cornell epiphytic mixes), aroids and other tropical houseplants.

Sources

  1. Soilless Substrate Management for Nursery Crops — University of Kentucky Nursery Crop Extension
  2. What are the alternatives to using peat-based compost? — RHS
  3. Indoor Plants – Soil Mixes — Clemson Home & Garden Information Center

Written in our own words from these sources. Check a product label before using any treatment.