My first best tip for naturally improving soil quality is going to be compost. I tend to recommend compost both as a way to naturally dispose of and "recycle" kitchen scraps, cardboard, and more from your home, and it's also a great and rewarding way to amend your soil naturally. Compost is a great source of organic nutrients like nitrogen, potassium, and more for your garden, and I've had great success using it over the years. I've noticed more growth in my established garden plants, and more bountiful harvests from whatever produce I'm growing that year. Compost is especially great for produce because you don't need to worry about any chemicals you might be introducing into your soil through commercial fertilizers. Another tip I have is to use plants to improve your soil quality! This could mean using plants with especially vigorous roots to break up compacted or clay soil to allow other plants to thrive, or selecting your plants carefully and companion planting to ensure all of the plants in your garden are prioritizing certain nutrients. This will mean your soil doesn't get depleted in just one nutrient, and can instead maintain a much more balanced profile throughout the year.
Hands down, the most effective natural method I've used is adding well-rotted chicken manure mixed with wood shavings and/or straw. When I started using it in a no-dig setup a few years ago, I'd layer composted manure mixed with straw over the beds in late autumn, cover with black plastic sheeting and let the worms do their thing over winter. By spring it was like chocolate cake down there. Crumbly, dark, rich, and full of life and worms. I noticed the colour of the leaves was deeper green, the yield was higher, and the soil held moisture better between waterings--especially noticeable during hot, dry spells. Another big plus? Fewer weeds. A combination of the warmth from the rotting process starting the unwanted seeds off germinating and the thick mulch from the bedding smothered most of the opportunists. Less work for me.
One of the most effective natural methods I've used to improve the soil quality in my garden is the incorporation of compost. Compost is a rich resource for adding nutrients back into the earth; it enhances the soil structure, thereby promoting better root growth and water retention. Over time, I noticed that after mixing compost into my garden beds, the soil became more friable and darkened—a clear indicator of increased organic matter. The impact on plant growth was equally remarkable. Plants seemed more vigorous and healthy, with an evident increase in both foliage and blooms. For instance, my tomato plants yielded more fruit, which was not only larger but also richer in flavor compared to previous seasons before I started composting. This natural approach not only boosts plant health but also helps the environment by recycling kitchen and garden waste, making it a sustainable choice for garden upkeep.