Mulch that has stopped letting water through, and how to fix it before spring
Mulch laid a year ago is usually not doing the job it was laid for. The layer has settled and broken down to something like half the depth it started at, the surface has knitted into a felted crust, and water that lands on it runs sideways to the edge of the ring rather than going down. From the driveway the tree still looks mulched. At the root zone it is close to bare.
Sort it out before the warm months rather than during them. A layer that sheds water turns every watering into a partial one, and you will not notice, because wet mulch goes dark on top and looks exactly like mulch that is working.
Find out how deep the layer actually is
Push a trowel straight down through the mulch at four or five points around the ring, near the edge as well as close to the trunk. You are looking for 75 mm of loose material sitting on soil. What you usually find on a ring a year old is a thin skin of coarse chip over a dark band of rotted material that has become part of the soil surface. That band is soil now, and it does not count towards your depth.
Check the width while you are down there. A ring that was generous when the tree went in has usually been mown into, edged back, or outgrown by the canopy. The ground worth covering is the ground the canopy shades, and mulch that stops short of that leaves the outer roots, the young absorbing ones, working in bare warm soil.
A bucket of water will tell you whether it still lets water through
Pour half a bucket slowly onto one spot and watch. Mulch in good order takes it straight down and the wet patch barely spreads sideways. Mulch that has turned water repellent beads for a second, then flattens out and runs. Wait a minute, then dig into the wet patch with the trowel. If the top is damp and the material below it is dust dry, the layer is shedding.
The better test costs no effort. Go out the morning after decent rain, lift a section of mulch near the trunk and another near the edge, and put your hand flat on the soil. Wet mulch over dry soil is the whole diagnosis. It happens most with fine textured products, with anything carrying a lot of sawdust and fines, and with any layer that has dried hard and then bound together with fungal threads.
Break the crust before you add anything
Tipping fresh chip onto a sealed layer buys you nothing. The new material soaks up the first watering for itself and the crust underneath goes on shedding whatever gets past it. Take a fork or a hard rake and work the existing layer over, breaking the felted skin and turning the material loosely. Where the rotted band has set into a sheet you can lift in pieces, take it off and put it on a garden bed.
Work the mulch, not the soil. Forking through a root zone is not the same as turning a vegetable patch, and the fine roots just under the surface are the ones the tree relies on. If the material is badly repellent, a soil wetting agent watered in after you have opened the layer up will help it accept water again. That is a short term measure. The lasting fix is coarser mulch at proper depth, because a layer deep enough not to dry right out does not turn repellent in the first place.
Top up to depth, then water the mulch itself
Bring it back to 75 mm of loose material, measured with the trowel rather than judged by eye, and take the ring out as wide as the site allows. Coarse chip with some structure stays permeable far longer than a fine dark product that looks tidy on the day it goes down.
On what to buy when you top up, Nursery Direct's mulching guide compares the common materials and how much of each a tree ring needs.
Then reset the gap at the trunk. Over a year the ring creeps inward: material washes in, mowers throw clippings, and the trunk ends up standing in damp mulch. Pull it back until you can see clean bark and the root flare sitting above the mulch line, and keep the doughnut shape rather than building a mound. The shape and the reasoning are set out in our guide on mulching, doughnut not volcano.
The last step is the one that gets skipped. Dry mulch is thirsty. Fresh chip will take most of the first watering for itself, so if you top up and then water as normal, very little reaches the soil. Water the ring heavily once the new material is spread, enough to wet the full depth, then check underneath with the trowel.
What this changes for a tree still establishing
A tree in its first year is watered on a set pattern: 150 to 200 litres, weekly for the first month, then fortnightly for around six weeks, then only in prolonged dry spells. All of that assumes the water arrives at the root ball. A repellent layer turns a full watering into a partial one, and the tree that then sulks gets blamed on transplant shock when the cause was a crust you could have lifted in one piece.
If you are running drippers, lift the mulch and check the emitters sit over the ball itself rather than out on the backfill. Site soil and root ball soil are different textures and water follows the easier path, so you can have moist backfill around a dry ball. There is more on that in watering and establishment.
None of this takes long. An hour with a fork, a trowel and a bucket will tell you what state a ring is in and put it right. If you are not certain what you are looking at, the planting library covers the rest of the establishment work, and we are happy to talk a job through.