The start of autumn and spring marks the time to amend soil in the garden and get ready for the next growing season. Here’s how to do it and amend soil for leafy plants, root vegetables, fruiting plants and Australian natives.
When I first started gardening, I had no idea what to do and where to start. I bought cheap soil and used a combination of liquid fertilisers alternating fortnightly with a seaweed tonic. As my growing space expanded along with my knowledge, that job became too onerous particularly with filling watering cans and carrying them around the garden. Now I concentrate on amending the soil before the start of the major growing seasons (autumn and spring), then supplement it mid-season and occasionally use liquid fertilisers and seaweed tonic for a quick boost or when needed. Here are the steps I follow.
How to Amend Soil at the Start of the Growing Season
Before I start amending soil at the start if each season, I check the BOM for the weather forecast to avoid extremes of temperature and periods of rain. Autumn can still be very hot in Sydney and early spring can bring on incessant rain which is better avoided as it can wash out a lot of nutrients in newly-amended soil.
1. Remove Spent Plants
Start by removing plants that have reached the end of their life cycle. While this may be an obvious step, sometimes we hang on too long for a couple of slow-growing beans and tomato plants that have stopped producing. I simply remove the spent plants before pests such as aphids, scale and mealy bugs attack them and spread diseases to the rest of the garden. I then dispose of them in the greens bin as I don’t have a compost in my tiny garden. If you’re a fan of no dig gardening, you could snip them at the very base or soil line leaving the roots intact and undisturbed. But as my garden consists largely of containers that have limited depth and raised beds that rest on soil that’s 5-15cm deep over concrete, I prefer to remove the plants, roots and all. I will address no dig gardening in more detail in another article.
2. Clean Up the Roots
Using a hand fork, break up the soil removing clumps of roots in the process. At this stage of the growing season, the soil may be compacted, dry and depleted of nutrients. Breaking up the soil aerates it and mixes the top and lower layers thoroughly before adding any amendments. In the past, I used to sieve the soil to remove large debris. As for what to do with clumps of fine roots, if they come from a healthy plant, I simply dump it over in an unused and hidden part of the garden and leave it to decompose naturally – a quasi compost system if one stretches the imagination.
3. Add Soil Amendments
When it comes to adding soil amendments, the choice is dependent on what I’ve grown in the past and I’ll be growing next in that container or raised bed. This is an important consideration when growing root vegetables that don’t need high amounts of nitrogen to avoid growing excessive leafy greens at the expense of roots and whether I’m amending soil for Australian native plants.
Keep Crop Rotation in Mind
Crop rotation is recommended if you have the space in your garden. In my tiny courtyard garden, I have very limited space and as such I practice crop rotation if it works with my planting schedule. This is the process I follow:
Heavy feeders such as tomatoes, zucchini and broccoli are followed by light feeders such as carrots, radish, beetroot, parsnip and spring onion. These are in turn followed by heavy “givers” such as beans, peas and broad beans which add nitrogen to the soil. These are followed by heavy feeders and the cycle starts again.
A. How to Amend Soil for Herbs and Leafy Vegetables
As a general rule, for herbs and leafy vegetables, I add organic or mushroom compost, worm castings, blood and bone which includes potash, pelletised chicken manure, mix it well then top it with a premium potting mix.
B. How to Amend Soil for Root Vegetables
For root vegetables, I add organic compost or worm castings, (not mushroom compost), pelletised chicken manure, mix it well then top dress it with a good inch or two of premium potting mix. In the past, I have added a little phosphorus which helps in root development and ended up with dense roots.
C. How to Amend Soil for Fruiting Plants
For fruiting plants such as chillis, tomatoes and eggplant, I add organic or mushroom compost, worm castings, blood and bone which includes potash, pelletised chicken manure and supplement it with a little sulphate of potash at the time of planting. This trace element helps with flowering and fruiting and gives them a boost of potassium. I usually follow up mid-season with another application of sulphate of potash which helps them produce more fruit later in the season.
D. How to Amend Soil for Australian Natives
For Australian natives, whether edible or not, the rule is ‘less is more’. I add very little blood and bone, worm castings, organic compost and a small amount of pelletised chicken manure and top up if needed with quality potting mix.
Mushroom compost tends to be more alkaline than organic compost and a lot of Australian natives struggle with it as it can hinder the plants’ ability to take up nutrients. In the past, I have killed a couple of Australian native plants with mushroom compost kindness so I avoid it altogether on natives.
4. Water and Wait
Water well and deeply then leave the amended soil alone for a week or so, keeping it moist but not too wet. The nutrients will start to meld together then it’s ready for planting seedlings or sowing seeds for the next growing season.
Products I Use
Without naming brands, I use a premium potting mix that has the Australian standard red tick. It contains a wetting agent with a controlled release of nutrients. The blood and bone product I use comes with sulphate of potash. I use pelletised chicken manure as it’s more convenient than other manures and stores well. Naturally, worm castings come from my garden.
When it comes to liquid feeds during the growth cycle, I avoid using them on root vegetables and Australian natives as they tend to be high in nitrogen, opting for a seaweed solution.
Reuse & Amend
In keeping with the sustainability ethos of my garden, I reuse all potting mix if it is not diseased. It may be dry and depleted of nutrients but after amending the soil, it gets a new lease of life.
The biggest joy I get is when I have transformed soil from a planter that was a dried up, hydrophobic clump to healthy, crumbly soil with happy earthworms.
Feed the soil first and it will in turn feed your plants.