If you take a look at Perth’s soil composition, it’s hard to ignore the massive impact soil pH levels have on the types of plants that grow in our region. You may have noticed the soil in your garden is more like sand than anything else, and perhaps your plants aren’t growing as well as you’d like – to fix these issues, you’ll need to look at your pH levels. Any good landscape architect worth their salt knows Perth’s soils are generally more alkaline, which makes gardening difficult even for the experts. So what does this mean and how can it be fixed?
Whether you’re looking at planting something new, redesigning your garden, renovating, or getting set up in a new property, here’s how to navigate alkaline soils and get your garden looking lush and green again.
All soils will have a certain amount of acidity or sourness, as well as a certain level of alkalinity or sweetness. This is what’s known as pH levels. Different soils can be categorised based on their pH level. The soil pH scale of 1-14 makes it easy to understand different soils and their pH levels. Soils below 7 are considered acidic, and soils above 7 are considered alkaline.
But why is that important?
Essentially, different plants are accustomed to different soil conditions, and soil pH levels affect a couple of critical plant growing features including:
- Soil bacteria – different pH levels affect how effectively bacterial activity releases nitrogen from organic matter.
- Nutrient leaching – pH levels below 5 can accelerate how quickly plant nutrients leach out of soils
- Toxic reactions – aluminium can become toxic to plants in pH levels below 5
- Soil structure – in dense soil structures like clay, extreme pH levels can dramatically impact the workability and cultivation of these soils as well as plant growth.
It’s easy to find out your soil pH levels by doing a home test with a soil pH detection device which will be available at any well-meaning garden centre. For a more detailed analysis of your soil quality, you could also submit a soil sample with your local laboratory for testing. Either way, finding out what soil you’re working with is a good starting point.
Alkaline soils (above 7 on the pH scale) can be particularly difficult to work with, and add a whole new element to the landscaping mission. That’s because alkaline soils typically lack important nutrients and minerals such as iron, manganese, zinc, copper, and boron. Here are a few ways you can balance out these deficiencies:
- Decrease pH levels by adding iron sulphate into your fertiliser, or watering routine.
- Add more compost, organic materials like leaf litter, manure, and mulch – these will work to raise the acidity (lower your pH levels) and create a more hospitable growing environment for your plants.
- Monitor and adjust your pH levels over time to ensure they stay within your desired range.
- Be gradual, not sudden in changing pH levels – going for a quick fix rarely works as overcorrecting your soil pH can negatively impact plant growth.
- Consider using store-bought natural garden soil – especially for raised garden beds and vegetable patches – make sure the pH levels are better than your original soil before buying.
- Choose plants that enjoy a bit of alkalinity. Some plants like alkaline soils better than others, so picking out plants that prefer higher pH levels is a smart way to tackle the issue.
Choosing your plants carefully is a great strategy in designing your garden in alkaline soil conditions. Generally, choosing native species is a foolproof way of making sure soil conditions are well matched to the plant’s needs. Natives are well adapted to thrive in local conditions. Here’s a mixture of plants that like alkaline soil to include in your garden:
- Rottnest island cypress
- Western Australian peppermint
- Tipuana tipu
- Candle nanksia
- Butterfly bush
- Guichenotia ledifolia
- Spider net grevillea
- Correa pulchella
- Coastal melaleuca
- Seaside Daisy
- Linnaea × grandiflora
- Grey Cottonhead
- Running postman
- Native wisteria
Here at Luke’s Landscaping, we’ve done our fair share of alkaline soil gardening and know a thing or two about working with low-quality soils. Designing a garden in alkaline soil can be challenging, especially in Perth’s typical sandy backyard, but with years of experience in the business of healthy gardens, you can trust we’ll get your garden green and flourishing in no time.