The Complete Guide to Selecting and Calculating Soil for Your Wooden Planters

Written By Tiliwood .

A practical guide for New Zealand gardeners on choosing the right soil, calculating quantities, and getting the most from your Tiltwood planters

Getting Started with the Right Soil

Congratulations on your new wooden planter! Whether you've purchased one or built your own, selecting the right soil is crucial for thriving plants and long-lasting results. Here in New Zealand, our unique climate and growing conditions require specific consideration when preparing your planter box.

Which Soil Should You Choose?

Not all potting mixes are created equal, and what works in your garden beds won't necessarily work in a planter. Here's what you need to know:

Premium Potting Mix vs. Garden Soil

For wooden planters, a high-quality potting mix is almost always better than garden soil for several reasons:

  • Better drainage – Prevents water-logging, which can rot wooden planters from the inside

  • Lighter weight – Easier on your planter's structure and more manageable if you need to move it

  • Fewer weeds and pathogens – Quality mixes are typically sterilised

  • Consistent texture – Garden soil can become compacted over time

What to Look For in NZ

When shopping at your local garden center, look for potting mixes that:

  • Are labeled for container gardening

  • Contain a mix of compost, bark, pumice or perlite for drainage

  • Include slow-release fertilisers (saves you time later)

  • Are pH balanced for the plants you intend to grow

For vegetable planters, choose organic mixes when possible. For ornamentals and shrubs, standard premium potting mixes work well.

Regional Considerations

Different regions in New Zealand may require slight adjustments:

  • Auckland and Northland: In these warmer, more humid areas, ensure excellent drainage to prevent root rot

  • Wellington and coastal areas: Choose mixes with good moisture retention but that won't become waterlogged in windy, rainy conditions

  • South Island: For cooler regions, darker soil mixes that absorb more heat can help extend your growing season

Remember that local garden centers often create mixes specifically formulated for your region's conditions - these can be worth the investment.

How Much Soil Do You Need?

This is where many gardeners go wrong - either buying too much (wasting money) or too little (making a second trip necessary).

Use Our Soil Calculator

To determine exactly how much soil you'll need for your planter, use our Soil Calculator Tool to get precise measurements. Simply enter your planter's dimensions, and we'll calculate the volume in litres.

Quick Estimation Method

If you prefer a quick estimate:

  1. Measure your planter's length, width, and depth in centimeters

  2. Multiply these three numbers together

  3. Divide by 1000 to convert to litres

For example, a planter that's 100cm long × 30cm wide × 40cm deep: 100 × 30 × 40 = 120,000 cubic centimeters = 120 litres of soil

Remember to leave about 2-3cm from the top edge to prevent overflow when watering.

Where to Source Quality Soil in New Zealand

Local Options

Quality potting soil is available from:

  • Garden centers – Palmers, Kings Plant Barn, and local nurseries often have their own premium mixes

  • Hardware stores – Mitre 10 and Bunnings carry several good options

  • Landscape suppliers – Can deliver larger quantities if you have multiple planters to fill

  • Specialised organic suppliers – For vegetable and herb planters

Cost Considerations

Expect to pay between $12-25 for a 40L bag of quality potting mix. While it might be tempting to go with the cheapest option, investing in quality soil pays dividends in plant health and reduced maintenance.

Preparing Your Tiltwood Planter

Before adding soil to your wooden planter:

  1. Add drainage – While our Tiltwood planters are designed with drainage in mind, adding a 2-3cm layer of small stones or pumice at the bottom can improve drainage further

  2. Consider lining – We do recommend lining your planter if growing edibles. For extremely moisture-loving plants, consider lining your planter with plastic (punctured for drainage). 

  3. Positioning – Place your planter in its final position before filling, as it will become significantly heavier

Maintaining Soil Health Throughout the Seasons

Spring Refresh

As spring arrives in New Zealand (September-November), your planter soil will need:

  • Top-up of fresh potting mix (soil settles over time)

  • Addition of slow-release fertiliser

  • Mulching to retain moisture as temperatures rise

Summer Care

During our hot NZ summers (December-February):

  • Water more frequently as wooden planters can dry out faster than in-ground gardens

  • Add moisture-retaining products like water crystals or coconut coir

  • Apply mulch to reduce evaporation

Autumn/Winter Preparation

As temperatures cool (March-August):

  • Reduce watering frequency

  • Consider adding gypsum to break up compacted soil

  • For winter vegetables, add compost to improve soil structure

When to Replace Your Soil

Unlike garden beds, planter soil doesn't rejuvenate naturally and will need complete replacement every 1-2 years. Signs it's time to replace include:

  • Water running straight through without being absorbed

  • Plants showing nutrient deficiencies despite fertilising

  • Soil becoming compacted and hard

  • Persistent fungal issues or pests

Final Tips for Planter Success

  • Companion planting works well in larger planters – mix flowers with vegetables or herbs

  • Avoid over watering – the number one cause of issues in wooden planters

  • Consider your planter position – most vegetables need 6+ hours of sunlight

  • Match plant needs to soil depth – shallow-rooted plants for shallow planters

Ready to calculate exactly how much soil you need? Use our Soil Calculator Tool for precise measurements tailored to your Tiltwood planter dimensions.

Tiliwood .