Compost Heaps in the Backyard Forest

What should we do with all of those invasive plants after we’ve pulled them out of the ground? My preference is to compost them on site to help maintain local soil fertility, and I’ve developed a few preferences that I thought might be worth sharing.

Keep Them Smallish

Many small heaps (3-5’ diameter) are better than a few large heaps (6-10’ diameter), less visible, less fuel for potential fires, and shorter carry distances. Stack them too high and they can easily topple.

Build a Base

A base of dead wood prevents the roots or stems of the removed invasive plants from touching soil and continuing to grow.

Contain Them

Trim the sticks and branches in the base so they don’t stick out beyond the perimeter. It’s preferable to be able to walk completely around the compost heap.

Maintain Them

Check them regularly for invasives that have survived and are still growing. Similar to stirring a fire to keep it burning, turn over the plant debris to mix it up, keep the air circulating, and the decomposition process going.

Dismantle and Spread When Possible

Over time, as the volume of invasive plant debris shrinks, dries up, and/or becomes compost, the heaps can be dismantled. I like to spread the remaining large sticks and limbs around the immediate vicinity. If they are lying directly on the ground, they will decompose more quickly. One study (here) found that for unknown reasons, the presence of abundant deadwood on sites increased the germination and survival of conifer saplings.

Worst-Case Scenarios

No Base — I’ve seen numerous Holly and Laurel thickets that resulted from the practice of cutting off limbs and branches and leaving them lying directly on the ground where they re-rooted over the winter. Ivy left on the ground can re-root as well.

Too Much soil — Too much soil left in the invasive debris increases the odds that invasive plants keep growing on the heap.

Fire Hazards — Any large compost heap, especially one beneath a conifer with low hanging branches, can become a fire hazard. I once built a haystack-sized pile of Ivy that spontaneously combusted on a hot summer day. Luckily it didn’t ignite a forest fire.

Tightly Packed or Piled Loosely?

I don’t think it matters too much whether the invasive debris on the heap is tightly packed or piled loosely. If it’s tightly packed, it is more likely to decompose quickly but also more likely that invasive plants will keep growing. If piled loosely, it’s more likely to dry out, but will take longer to decompose. Finding the happy medium is part skill and part luck, dependent on a host of variables —  kind of like building the perfect campfire.