Cover crops versus weeds: first trial results

Cover crops are often pitched as the clean regenerative alternative to herbicides. Our first trial at Kawa Tamu says: not so fast.

When we cleared bushy indigenous vegetation to establish our coffee plots, weeds came back within weeks: couch grass, blackjack and broadleaf species reclaiming the ground almost as fast as we could slash it. In February 2026, we planted five cover crops alongside the coffee (jack bean, sunn hemp, desmodium, maize and centrosema), spaced two feet apart, to see which could hold that ground for us.

The result: two of the five, desmodium and centrosema, barely germinated and were overtaken by weeds almost immediately. Jack bean (Canavalia) was the standout of a mediocre field. It's covering roughly half the ground, though weeds are still finding their way through the other half.

We're now testing how best to cut back the jack bean, just above the nodes so it resprouts, rather than replanting for a second season. We don't yet know if that will hold weed pressure down long enough to be worth it.

What this trial confirms so far: no cover crop we've tried removes the need for manual work. Hand-weeding around the coffee planting circles and brushcutting between rows are still doing most of the real weed suppression on this farm.