A newly planted tree that droops, yellows or drops leaves could have too much water or too little. From a distance the two look almost the same, so the leaves alone won't tell you which. The soil around the root ball will, and checking it takes two minutes and a trowel.
Why the first weeks are tricky
An advanced tree or hedge plant arrives with its roots packed into a ball of potting mix, which behaves very differently from your garden soil. For the first few months the roots stay mostly inside that ball, so what matters is how wet the root ball is, not the bed around it. This catches people out in two ways:
- In clay soil, the planting hole can fill with water like a bath and hold it for days. The root ball sits in it and the roots run short of air.
- In sandy soil, water drains straight past. A light sprinkle wets the top few centimetres and the root ball underneath stays dry. Sandy soils can also turn water repellent in summer, so water beads and runs off instead of soaking in.
Either way, the surface tells you very little.
Signs of underwatering
- Leaves wilt in the morning, not just in the afternoon heat
- Leaf edges turn brown and crisp, starting with the newest growth
- Leaves curl or fold inward to save water
- The root ball has shrunk away from the surrounding soil, leaving a gap or crack
Some afternoon wilting on a hot day is normal for a new plant. If it has perked up by evening, it's coping. If it's still limp the next morning, it's thirsty.
Signs of overwatering
- Older, lower leaves turn yellow and drop, often while still soft
- Leaves wilt and stay limp even though the soil is wet
- New growth is pale, small or blackened at the tips
- Water is still sitting in the watering basin hours after you've watered
- The soil smells sour, or green algae or moss grows on the surface
- The bark at the base of the trunk is dark or soft
Wilting with wet soil is the key sign: waterlogged roots stop taking up water, so watering more makes it worse. Our guide to overwatered plant symptoms explains what is going on at the roots in more detail.
The finger and trowel check
- Pull the mulch back on one side of the plant, at the edge of the original root ball.
- Push a finger in 5 to 10 cm. For a small hedge plant this is often enough.
- For an advanced tree, dig a narrow hole with a trowel 15 to 20 cm deep at the edge of the root ball, and take a handful of soil from the bottom.
- Squeeze it in your fist.
- Push the soil back and replace the mulch.
What the squeeze tells you:
- Dust or loose crumbs that won't hold together: too dry. Water deeply today.
- Holds its shape, then breaks apart when you poke it: about right. Leave it and check again in a few days.
- Sticky, shiny, leaves your hand muddy or drips water: too wet. Stop watering and check again in three or four days.
Do this check every few days for the first month, and always before you water. It's the same idea as these soil checks for potted plants, just dug deeper. Cheap moisture meters often read wrong in sandy or salty soil, so trust your hand.
How to water when it does need it
- Water deeply, then wait. A slow soak that reaches the bottom of the root ball beats a daily sprinkle. As a rough guide, a hedge plant from a 200 mm pot might take 5 to 10 litres at a time, and an advanced tree from a 45 litre bag 20 to 40 litres. Let the check tell you when to water again.
- Build a watering basin. A low ring of soil around the root ball holds water where the roots are. In clay soil keep the ring shallow, so you aren't building a pond.
- Water slowly. A hose on a trickle for 15 to 20 minutes, or a bucket with a few small holes in the bottom, soaks in instead of running off.
- Water early in the morning in summer, so less is lost to evaporation.
- Mulch 5 to 7 cm deep, but keep it a hand's width away from the trunk.
- Use a soil wetting agent if water beads on sandy soil.
- Check your local water restrictions before setting a routine.
When to back off
Cut back watering when the check says the soil is still moist, after good rain, and through cooler months, when new plants use far less water. A dry, windy northerly or a heatwave is the time to check more often, not to water by the calendar.
Over the first one or two summers the roots grow out into the surrounding soil. As that happens, water less often but just as deeply, so the roots follow the water down rather than staying near the surface.
When it isn't the water
Some leaf drop in the first fortnight is normal transplant shock. Leaves browning on one side only usually point to wind or sun. If the soil check is right and the plant keeps going backwards, look for pests, stake rubbing or a trunk planted too deep, and ask your nursery. Photos of the leaves, the trunk base and a handful of root ball soil will tell them more than a description.
Alexander Novak writes for Leaftell (leaftell.com), a plant care site that helps you work out what's wrong with a plant from a photo.
