A long, wet winter leaves its mark on trees in ways that are not always obvious until the weather warms up. Waterlogged soil, weeks of low light and the odd storm can weaken roots, invite fungal problems and loosen anchorage. Then September and October arrive with their gusty westerlies and equinoctial gales, just as trees put on a heavy load of new leaves. That combination is why spring is one of the most useful times of year to walk the section and take a careful look at every tree of any size.
None of the checks below need special equipment. A notebook, a phone camera, a pair of binoculars for the upper canopy and an hour on a fine day are enough.
Start at the ground
Problems usually show first at the base of the tree. Waterlogged soil starves roots of oxygen, and fine roots die back after several weeks of saturation. Trees on heavy clay, in hollows or downslope of hard surfaces are the most exposed.
- Look for soil cracking or mounding around the base, particularly on the side opposite any lean. This can mean the root plate has shifted.
- Check for mushrooms or bracket fungi at the root flare or on surface roots. Some are harmless, but certain species indicate root or butt rot.
- Note any areas where water still lies a week after rain. Persistent ponding near a tree suggests drainage problems that will recur.
- Look for soft, sunken or weeping bark near ground level, which may point to collar rot.
A tree that has developed a new lean since autumn deserves prompt attention from a qualified arborist, especially if it could reach a house, driveway or road.
Work up the trunk and into the crown
Next, walk slowly around the trunk. Vertical cracks, cavities, oozing sap and loose bark are all worth noting. Where two main stems meet in a tight V with bark trapped between them, the union is weaker than one with a wide, ridged joint, and wet-season storms often expose this weakness.
In the crown, binoculars help pick out:
- Hung-up branches broken by winter winds and caught in the canopy.
- Dead limbs with no buds swelling while the rest of the tree is breaking into leaf.
- Splits where branches join the trunk.
- Thin or patchy new growth compared with previous springs.
On deciduous trees, the timing of bud break is a useful health signal. A tree that leafs out weeks behind others of the same species nearby, or only on some branches, may be under stress.
Watch the weather as well as the tree
Spring in New Zealand is famously changeable. Strong winds are common through September and October, and a tree with a weakened root system is most likely to fail when saturated soil coincides with a gale. Keeping an eye on forecasts from MetService helps with timing: it makes sense to clear the area under a doubtful tree, move a car or delay outdoor work when severe wind warnings are issued.
Late frosts also cause damage in inland areas. Fresh growth on citrus, avocado and tender ornamentals can be burnt overnight, leaving blackened tips that look alarming. Most trees recover, but repeated frost damage on young trees is worth noting for future planting decisions.
What to do with what you find
Most of what turns up on a spring walk is minor: a few small dead twigs, a little moss, some storm-damaged leaves. These need no action, or a light tidy with secateurs. Larger findings need more thought.
Dead or broken limbs larger than about wrist thickness, especially over paths or play areas, are worth having removed by an arborist. Fungal fruiting bodies at the base, new leans and splitting unions call for a proper assessment, which typically costs a few hundred dollars and can save much more. Ongoing drainage issues may need a soakhole, a drain or a change in how stormwater from the roof and driveway is directed.
If planting new trees this spring, choose positions that avoid the problems seen over winter. Low spots that held water are poor choices for most species, and soils that stayed sodden may need improving first. The challenges are particularly sharp on heavy soils near new paving, a topic covered in this guide to planting beside a driveway in clay soils.
Keep the notes and photos. Comparing them with next spring’s walk shows whether a crack is widening or a lean is increasing, which is exactly the sort of information an arborist will ask for.
Frequently asked questions
Can a wet winter kill a mature tree? Prolonged waterlogging can kill fine roots and lead to root rot, which weakens or eventually kills some species. Trees on poorly drained sites are most at risk.
Are mushrooms at the base of a tree always a bad sign? No. Many are harmless decomposers feeding on mulch or dead roots, but bracket fungi on the trunk or root flare should be identified by an arborist.
When is the best time to have a tree assessed after winter? Early to mid-spring, once the soil has drained a little and before the windiest weeks, gives time to deal with problems before they become urgent.