Don’t Rake the Duff: Four Reasons We Leave Avocado Leaves Where They Fall

If you have an avocado tree, you have leaves. Lots of them. Avocados shed all year, and the pile underneath builds into a thick, crunchy layer growers call the duff. The tidy instinct is to rake it up. Please do not.

We leave the duff under our trees on purpose, and there are four reasons. One of them is not entirely scientific.

Reason one: the dog loves it

We will get this one out of the way first. Our dog thinks a deep bed of avocado leaves is the best thing on the property, and nobody here is going to take that away. It is not a horticultural argument, but it is a true one.

Reason two: it keeps water in the ground

The duff works like a natural mulch. It shades the soil and slows down evaporation, so more of the water we put on stays where the roots can use it. That means we can water less. Growers use straw and wood-chip mulches for the same reason: to hold moisture and keep the soil cool. The flip side is that mulched ground stays wet longer, and Avocado Production in California: A Cultural Handbook for Growers, Book Two, warns that it is easy to over-water under a thick layer, so check the soil rather than watering on habit.

On a grove that pays for every gallon, that matters a great deal. Our guide to how much water an avocado tree needs explains why mature trees drink as much as they do, and anything that holds moisture in the soil for free is worth keeping.

Read nextCut, Don’t Yank: Picking Avocados With Pruners So They Last Longer

Reason three: it helps against root rot

Root rot is one of the most serious problems an avocado grower can have. The way it was explained to us, the rot tends to go after that duff layer rather than the roots underneath it, so a healthy layer of leaf litter helps protect the tree.

There is research behind that idea. Root rot (caused by Phytophthora cinnamomi) is still the most important disease problem in California avocados, and organic mulch is one of the main tools against it. The UC growers’ handbook explains that decomposing mulch is full of microbes that compete with the pathogen, releases enzymes that break down its cell walls, and can act as a trap where its swimming spores settle. Avocado roots growing in the mulch and at the mulch-soil boundary are relatively free of root rot, although roots deeper in the soil can still be infected. Growers are advised to keep at least 4 to 6 inches of coarse organic mulch under the canopy, pulled several inches back from the trunk, and to top it up now and then with mostly ground wood, which controls root rot better than naturally dropped leaves. So the duff is a good start, not the whole answer. It is not a cure, and a tree that is already declining needs a proper look. We walked through some of the warning signs in diagnosing a dying avocado tree.

Reason four: it feeds the soil

Over time the leaves break down and return nutrients to the soil. The tree effectively feeds itself from what it drops: the handbook notes that avocado feeder roots near the surface are very efficient at recycling nutrients from decomposing leaf mulch, one reason California groves have relatively few mineral deficiencies. Raking the leaves away and hauling them off means taking that out of the ground and, sooner or later, buying it back as fertilizer.

It also protects the feeder roots. Avocado roots sit very close to the surface — 80 to 90 percent of the feeder roots are in the top eight to ten inches of soil — which is exactly why we say you should not grow plants under the canopy. A rake, dragged hard enough, can disturb those same shallow roots.

Adding mulch where the duff is thin

Under a young tree, or anywhere the leaf layer has not built up yet, we add mulch instead of waiting for it. Bare soil in the sun dries out fast and runs hot right where those shallow feeder roots are working.

A mulch layer does three more jobs on top of holding water:

• It buffers temperature. The root zone stays cooler on hot afternoons and holds a little warmth on cold nights.
• It slows erosion. Rain and sprinkler water hit the mulch instead of the soil, so less topsoil moves.
• It stops crusting. Covered soil stays loose, so air and water keep reaching the roots.

How we put it down: coarse material such as aged wood chips or shredded prunings rather than fine compost, which can pack down and shed water; 4 to 6 inches deep under the canopy, tapering at the edges; and pulled several inches back so it never sits against the trunk.

So what do we actually do?

Nothing, mostly. The leaves fall and stay. Paths and walkways get cleared where people need to walk, but the ground under the canopy is left alone to build up.

The fruit that comes off those trees is what goes into our 4lb Hass box and 6lb Hass box, which ship free in season. Between harvests, the waitlist on either page will email you when fruit is back. Until the trees are picking again, the avocado scoop, the Hawaiian shirt and our hats ship year-round.

This post is part of our guide to growing avocado trees.