Acid soil in your garden: how to test and adjust pH

TL;DR

Acid soil (low pH) can be an asset (rhododendrons, azaleas, heathers thrive) or a problem (most vegetables want neutral). Test your pH with a simple kit (pH 4-6 = acid, 6-7 = neutral, 7+ = alkaline). Solutions: if pH is acid, use acid-loving plants; if you want neutral, add lime.

What is pH and why does it matter?

pH is the scale from acid to alkaline (basic). The scale runs 0 to 14:

• pH 0-7: Acidic
• pH 7: Neutral (pure water)
• pH 7-14: Alkaline (basic)

Most garden soils fall around pH 5-8. Plants have preferences. Some love acid, some love neutral, some love alkaline.

Why does it matter? Because nutrient availability depends on pH. In very acid soil, nutrients may be present but plant roots cannot uptake them (bound up). In alkaline soil, iron becomes unavailable even if it is in the ground.

How to test pH

Method 1: pH test kit (cheap, home test)

Buy a soil pH kit from a garden centre (5-10 euros). Usually works like this:

1. Dig a soil sample from 10 cm depth (away from paths, not right near plants).
2. Let it dry (1-2 hours on a table).
3. Mix soil sample with the testing liquid in the kit (usually distilled water).
4. Shake, wait 5-10 minutes.
5. Compare color to color chart in kit.

Warning: Kits are rough (inaccurate +-0.5). Good enough for gardeners. For precise tests, see method 2.

Method 2: Digital pH meter

Cheap digital pH meters cost 20-50 euros. Tips:

• Test when moist (moisture content matters, not bone dry).
• Insert probe into soil.
• Read value (usually digital display).

More reliable than kits.

Method 3: Lab test (precise, but slow)

A soil testing laboratory (university, agricultural service) tests your soil. Mail in a sample. Get pH, nutrients, texture, more.

Cost: 30-100 euros. Wait 1-2 weeks. Benefit: precise data.

What pH does your garden want?

Vegetables (nearly all): pH 6-7 (slightly acid to neutral)

• Tomatoes, beans, lettuce, garlic, carrot all want this.

Fruit:

• Apple, berry: pH 6-7
• Blueberry: pH 4.5-5.5 (acidic!)

Ornamental:

• Acid-loving (pH 5-6): Rhododendron, Azalea, Heather (Calluna), Pieris, Kalmia
• Neutral (pH 6-7): Roses, Hydrangea (blue in acid, pink in alkaline), Lavender, Hardy Fuchsia
• Alkaline (pH 7+): Lilac, Viburnum, Privet

Your soil is acid (pH 5-5.5): what now?

Option 1: Use acid-loving plants

If your pH is around 4.5-5.5, use this as an advantage. Plant:

• Rhododendron (Rhododendron simsii / R. ponticum) - wide range, beautiful blooms
• Azalea (Azalea indica/mollis) - colorful dwarf shrubs
• Heather (Calluna vulgaris, Erica carnea) - low growers, hardy
• Pieris (Pieris japonica) - evergreen, flowering
• Kalmia (Kalmia latifolia) - small tree, pink flowers
• Woodland shrubs: Wild honeysuckle, Holly, Daphne

This requires no adjustments. You already have what they want.

Option 2: Gently neutralise with lime

Want neutral for vegetables/roses? Add agricultural lime (CaCO3). This raises pH slowly.

Dosing (rough):

• pH 5.0 to 6.5: roughly 1-2 kg lime per 10 m2
• pH 5.5 to 6.5: roughly 0.5-1 kg per 10 m2

Timing: Autumn (October-November) or early spring (March). Work in top 10 cm. Rain helps.

Note: Lime works slowly. See results after several months.

Your soil is neutral to slightly acid (pH 6-6.5): ideal

This is perfect for most gardens. Vegetables, roses, many plants grow well. Change nothing.

Your soil is alkaline (pH 7+): consider it

This is unusual in the Netherlands (usually more acid), but possible in certain regions (chalky).

Consequences:

• Iron (Fe) becomes unavailable, plants yellow (chlorosis).
• Rhododendron, azalea dislike it.
• Lilac, viburnum, privet thrive.

Adjustments: Alkaline soil is hard to lower. Adding acid (sulfur) costs effort. Better: plant alkaline-tolerant species:

• Lilac (Syringa vulgaris)
• Viburnum (Viburnum opulus)
• Privet (Ligustrum vulgare)
• Mock-orange (Philadelphus coronarius)
• Roses (they like this)
• Lavender, Rosemary (prefer chalky)

How often to test pH

First: test now (baseline). Yearly: retest in spring. If you added lime: retest after 2 months.

Most gardens change slowly. Acid regions stay acid, alkaline stay alkaline.

Frequently asked questions

My soil is acid, but I want vegetables. What now?

Add lime. Incorporate 1-1.5 kg lime per 10 m2 in October/March. Retest after 2 months. Goal: pH 6-6.5 for vegetables.

Can I control hydrangea color with pH?

Yes! Hydrangea:

• Acid soil (pH 5-5.5): Flowers turn blue to purple
• Neutral (pH 6.5-7): Flowers turn pink to purple
• Alkaline soil (pH 7.5+): Flowers turn pink to red

This works because aluminum ion availability depends on pH. Acid soil = more aluminum = blue hydrangea. You can tune color by adding lime (alkalinize) or sulfur (acidify).

My rhododendron does not grow in "acid" pH 6.5. Why?

pH 6.5 is actually not acid enough for rhododendron. It wants pH 4.5-5.5. Are you missing something else:

• Water: Rhododendrons need good drainage, but also regular water.
• Air: Compacted soil? Loosen it.
• Shade: Rhododendrons in full sun can burn, prefer dappled shade.
• Drainage: Standing water? Install drains.

Check all four first before adjusting pH.

pH stays the same for years. Why?

Soil structure (clay, sand, silt) determines pH buffer. Clay holds acid/alkaline long. Sand changes fast. Dutch gardens usually clay-sand mix, so pH drifts slowly.

Which plants tolerate both acid and alkaline?

Many:

• Roses (prefer neutral/slightly acid, but tolerate broad)
• Lavender (tolerate broad)
• Hydrangea (tolerate broad, color changes)
• Forsythia (tolerate broad)
• Wild honeysuckle (tolerate broad)

Step-by-step

Step 1: Test your pH now

Buy a pH kit (5 euros) or digital meter (20 euros). Dig 3 soil samples (corners + centre) from 10 cm deep. Let dry. Test each. Average is your pH.

Step 2: Decide your target plants

What do you want to grow? Vegetables, roses, rhododendrons? Look up their pH preference.

Step 3: Adjust if needed

• Too acid (pH under 5): Plant acid-lovers (rhododendron, azalea).
• Just right (pH 5-6.5): Check your target plants. Adjust only if needed.
• Alkaline (pH over 7): Plant alkaline-tolerant (lilac, privet).

Step 4: Add lime (if needed)

Want to raise pH? Add lime in October/March, work into top 10 cm.

Step 5: Retest after 3-4 months

Is pH moving toward your goal? Yes = done. No = repeat step 4.

Frequently asked questions

Are there "quick" ways to change pH?

Not really. Lime works over months. Sulfur (acidify) works slowly too. Expect 2-3 months for visible change. This is not a "quick" operation.

Can I have acid-lovers and alkaline-tolerant plants in the same garden?

Yes, but harder. You can use raised beds for acid-lovers (own acid soil mix) and sunken beds for alkaline-tolerant. Or: plant acid-lovers in one corner (let pH stay naturally acid), alkaline-tolerant in another corner.

My rhododendron is dying. Could it be pH?

Possibly, but more likely drainage. Rhododendron needs:

• Loose, draining soil
• Regular water (not waterlogged)
• Dappled shade
• Low pH (4.5-5.5)

Check all four. If pH is right, it is something else.

Discover your own garden design

At [gardenworld.app](https://gardenworld.app) you can upload your front yard and see which plants suit your soil pH best - with realistic growth and bloom for acid, neutral, and alkaline species. Design your garden for your soil, not against it.