Tree Health Essentials: Soil, Watering & Disease Prevention

Trees are some of the longest-living organisms on earth, but they can only thrive if their foundations are solid. In the Western Cape, where weather swings from long, dry summers to sudden winter rains, soil, water, and disease management are the holy trinity of tree care.

This guide is your one-stop resource to keep your trees strong. It pulls together the essentials from our most popular blogs, plus expert tips from our arborist.

And if you want to go deeper on any single topic, you’ll find links to the full posts along the way.

Why does healthy soil matter more than you think?

Soil isn’t just “the stuff your tree stands in.” It’s a living, breathing ecosystem.

Beneath your feet are billions of fungi, microbes, and invertebrates working together to cycle nutrients, balance moisture, and keep your tree alive.

When soil is compacted, depleted, or has the wrong pH, your tree starts running on empty. Leaves yellow, growth slows, and suddenly, pests and diseases move in.

Healthy soil gives you:

• Better nutrient uptake → greener leaves, stronger growth.

• Resilience against drought → soil with organic matter holds water like a sponge.

• Natural disease resistance → beneficial microbes outcompete pathogens.

Want to learn how to test and improve your soil? Read our full guide: 5 Ways to Improve Your Soil.

How do I know if my soil is “good” or “bad”?

The fastest way? Test your pH.

• Most garden and fruit trees love a range of 5.8 – 7.0.

• Too acidic = roots can’t absorb calcium, magnesium, or phosphorus.

• Too alkaline = iron and manganese lock up, causing yellow leaves.

DIY test: Pick up a kit at your local nursery. Dig 10–15cm down, mix soil with water, and check the probe or strip.

Pro test: Send a sample to a lab, this gives you a full breakdown of nutrients and organic matter.

💡 Fun fact: Blueberries, azaleas, and conifers thrive in acidic soils (pH 5.0–5.5), while veggies, ornamentals, and lawns prefer slightly acidic (pH 6.0–6.5).

For a deep dive, see Understanding Soil Quality.

Can fungi really make my trees healthier?

Yes, and not the kind you fry with garlic butter!

We’re talking about mycorrhizal fungi: threadlike networks called mycelium that live in soil and connect trees to each other.

Think of it as the internet of the underground:

• It ferries nutrients and water between roots.

• It boosts trees’ immunity against certain diseases.

• It even lets older trees “feed” younger ones nearby.

Without fungi, trees are like WiFi devices without a router - isolated and weak. Mulching, avoiding chemicals, and adding compost all encourage these beneficial fungal allies.

More tips here: How to Increase Microorganisms in Your Soil.

Am I watering my trees wrong?

Most people are. The two biggest mistakes we see?

1. Watering too shallow → roots stay near the surface, trees stress easily.

2. Overwatering → suffocates roots and encourages rot.

Golden rule: Water slowly, deeply, and less often. Aim for the drip line (the circle where rain would naturally fall from the canopy).

Signs you’re doing it wrong:

• Wilted leaves despite daily watering → water is evaporating before it sinks.

• Fungal growth at the base → soil is staying too soggy.

• Stunted growth in summer → roots never got deep enough.

💡 Pro tip: Mulching with woodchips keeps soil cool and moist while feeding fungi and worms.

Get the full breakdown in The Do’s and Don’ts of Tree Watering

Why are my tree leaves sticky, black, or curling?

Nine times out of ten, that’s insects talking.

In the Western Cape, the biggest culprits are:

• Aphids & ants → Yellow spots, curled new leaves, sticky honeydew. Ants “farm” aphids, protecting them from predators.

• Red spider mites → Tiny, almost invisible pests that thrive in hot, dry summers. Look for fine webs and faded leaves.

• Sooty mould → The black, powdery coating that grows on honeydew. Not the real problem, just a symptom of insects feeding.

Treatment isn’t just about spraying. It’s about breaking the cycle:

• Encourage predators like ladybirds and lacewings.

• Control ants to expose aphids to predators.

• Wash leaves with water or mild soap.

• In serious outbreaks, use organic insecticidal soaps or horticultural oils.

We unpack it all in The Basics of Common Tree Diseases in the Western Cape and Understanding Sooty Mould.

What’s the biggest tree killer in South Africa right now?

Without a doubt: the Polyphagous Shot Hole Borer (PSHB). This tiny beetle has made its way into almost every province, carrying a fungus that blocks trees’ water transport system.

It attacks over 100 species locally - from avocados and oaks to iconic wild figs. Once infested, most trees cannot be saved.

Look for:

• 2mm “shot” holes in the bark.

• Sawdust (frass) collecting at the base.

• Oozing sap or sugary exudates.

• Sudden dieback of branches.

What to do:

• Don’t move firewood unless you know it’s clean.

• Report infestations early.

• Infected trees must often be cut and destroyed.

Essential reading: Understanding the Polyphagous Shot Hole Borer.

How can I protect my trees year-round?

Here’s your quick checklist for prevention:

• Test soil pH annually and add compost or organic matter.

  
  

• Mulch to lock in water and feed soil life.

  
  

• Water deeply, not daily sprinkles.

  
  

• Monitor leaves for sticky residue, spots, or webbing.

  
  

• Prune for airflow; pests love damp, crowded canopies.

• Plant pest-resistant species when possible.

• Call an arborist at the first sign of trouble.

Final word: Healthy soil = happy trees

Most tree problems we see in the Western Cape can be traced back to soil, water, or pests.

Get those three right, and your trees will reward you with decades of shade, fruit, and beauty.

If you’re unsure, don’t wait for things to get worse. A quick soil test or tree health consultation now can save you from losing a mature tree later.

Reach out to Overberg Arborists - we’re here to help you keep your trees thriving.

1. Book a FREE online consultation

2. Reach out to us directly on 0724558345