Whether you’re a newbie gardener who’s just starting out, or a professional gardener who’s won a mountain of awards for their produce, your garden needs the best soil to grow the healthiest plants.
And whatever type of soil you have, its condition can always be improved. Once you understand a little bit more about your earth, this can easily be done. I’m also going to cover:
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What’s the difference between soil, mulch and compost?
There are so many different natural and organic garden matters it can be nerve-wracking knowing where to begin. I’m going to start by explaining the main differences between soil and various garden matters, and how to use them:
Soil
The definition of soil, also known as humus, is the uppermost layer of the earth’s crust, which is full of life. It plays a vital role in sustaining life, from its complex blend of nutrients, organisms, minerals, bacteria, dead or decaying matter, air and water. The three main soil categories are clay, silt and sand – and each retains different amounts of water and nutrients, making them better suited to certain plants. It’s worth noting, there is no such thing as the ideal soil (or perfect texture) for all plants.
Compost
Compost, sometimes referred to as natural or organic matter, can be bought in bags from a garden centre or made in a compost bin at home. It’s a combination of unwanted food waste, like vegetable trimmings and fruit, with garden waste like grass clippings, branches and leaf mold that’s been left to rot. It’s highly nutritious and can be used all around your garden – for potting young plants, amending topsoil and reinvigorating houseplants. Compost is ready to be used when it’s brown, crumbly and smells like earth – not rotted vegetables.
Topsoil
Top soil is the top two to seven inches of good quality, healthy ground that’s teaming with life, bacteria and nutrients. It differs from ordinary earth by being more enriched with organic matter, making it better suited to growing crops, plants or grass seed. It can be used throughout your garden and be added to beds and borders. You may wish to combine it with native earth that naturally occurs in your garden.
Fertiliser
A fertiliser is any matter that boost a plant or earth’s diet. The three most important macronutrients your plants need to grow are nitrogen, potassium and phosphorus. There are thousands of super soil fertilisers available; organic fertilisers can be made from kitchen waste including coffee grounds, ash, biochar or egg shells, which can be worked straight into the earth. While synthetic fertilisers like Miracle Gro or Powerfeed can be diluted then watered into your chosen area.
Cover crops
Cover crops are plants specifically grown to enhance soil, they: stop weeds from growing, fix nitrogen in the ground, prevent erosion, aid ground and water conservation, help to store nutrients and keep pests and diseases at bay. They are commonly grown in vegetable gardens during the winter, and can usually be chopped directly into a bed and worked into the earth. Some of the best cover crops include Black Oats, Forage Rye, Mustard, Clover and Green Manure.
Peat
Peat is decomposed vegetation or plant matter that has formed in a wet environment without oxygen. It is available in two forms: a golden brown, fibrous material also known as sphagnum moss, and a dark sticky substance. While it’s highly nutritious and readily available, excavating peat from native peatlands, bogs or moors destroys local wildlife habitats and releases large amounts of carbon into the atmosphere. For this reason, the UK is currently trying to ban the use of peat.
Coconut coir
Coconut coir, also known as coir or coconut fibre is a soil conditioner. As well as adding a high level of nutrients into the earth, it retains up to nine times its weight in water while allowing water to pass.
Mulch
Mulch is any matter that can be added to the surface of soil to enhance its visual appearance, while supressing weeds, preserving moisture and enhancing ground health and fertility. There are lots of organic mulches ready to use, including hay, straw, wood chips, grass clippings, manure, cardboard, wool and newspaper.
Manure
Manure is animal waste that’s used to fertilise the ground. There are two types of manure; hot and cold. Cold manure comes from cows, rabbits and sheep, and can be used immediately. Hot manure comes from chickens, pigs and horses and must be composted (left to rot) for three or more months, to avoid burning plants. Once rotted, hot manure is dry and crumbly like earth and doesn’t smell.
When to use the different types of manure
There are several types of manure and some plants have a preference. This greatly depends on a plant’s type and preferred earth pH. Take a look at the charts below to work out what your garden needs and the best time of year to apply.
So, what are the different soil types?
Once you understand your garden, it’s very easy to make amendments. The three main gardening soil types are:
Clay
Clay soil is thick and heavy. It gets waterlogged in winter and cracks from excessive heat in the summer months. To amend clay soil, add compost, coarse sand (not beach sand) or peat moss .
Silt
Silty soil contains a healthy balance of clay and sand, making it the ideal earth for most plants. To amend silt soil, add gravel, compost, horse manure with fresh straw or coarse sand (not beach sand) .
Sand
Sandy soil is light, dry and cannot retain moisture. To amend sandy soil, add sawdust, aged manure, peat moss or humus.
What is soil health?
Describing ground as ‘healthy’ might sound a bit weird – surely it’s just dirt, right? Well, not exactly. Healthy soil supports its local environment and helps plants to grow big and strong. While the definition of healthy ground differs depending on an area’s biodiversity (e.g. woodland earth will be very different to city earth), it contains a cocktail of minerals, nutrients, dead plant matter, fungi and bacteria. But first, you must understand its three basic needs – water, air and food:
Water
Water is very important for plant life, but too much can wash away naturally occurring nutrients and minerals, and leave it waterlogged. From time to time, allow your ground to dry. You may wish to monitor the water level with a soil moisture meter – also known as a soil moisture sensor or a soil probe.
Air
Air is incredibly important for soil. The lighter and less compact your earth is, the easier your plant’s roots will grow. Moles are great for aerating the ground, as are burrowing insects like earthworms; you can easily encourage worms into a space with a warm layer of sheet mulching. You may wish to monitor your ground temperature with a soil meter, or dig and till the soil to lighten it.
Food
Food refers to healthy organic matter or fertiliser, which can be added to the surface of a bed as top dressing – or watered into the surface. Food is incredibly important to your ground; after all, healthy soil means healthy plants.
How to address a nutritional deficiency in soil
There are plenty of homemade or shop bought products designed to target specific nutritional deficiencies. Fruit, vegetables and plants grown in containers are at the most at risk of deficiencies, and are most likely to display signs of ill health.
Phosphorus deficiency
If the leaves on a plant grow slowly then turn a dull yellow, your soil may have a phosphorous deficiency. The simplest way to fix a phosphorus deficiency is to add manure, bone meal or rock phosphate.
Potassium deficiency
If the leaves on your plant turn yellow with a purple or brown tint around the edge, then deliver poor fruit or flowers, your soil may have a potassium deficiency. To fix a potassium deficiency, add a high-potassium fertiliser, like tomato feed or sulphate of potash.
Nitrogen deficiency
If the leaves on your plants become frail and yellow, then develop a pink tinge, your soil may have a nitrogen deficiency. There are two ways to fix a nitrogen deficiency. In the short-term, top-dress ground with poultry manure or a high-nitrogen fertiliser; in the long-term, top-dress with well-rotted, organic manure or compost.
Magnesium deficiency
If the leaves on your plant display a yellow tint between the veins, which sometimes tints red or brown then triggers early leaf fall, your soil may have a magnesium deficiency. To address a magnesium deficiency, combine 20g of Epsom salt with one litre of water, then water your ground three times over six weeks – where possible, avoid contact with leaves.
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How to test soil pH
It’s very easy to learn what kind of earth you have in your garden. You can either experiment with a do it yourself method, or pay for a service.
DIY garden soil testing
You will need:
- 1 empty jar (ideally with straight sides
- 1/3 of a jar of earth
- Water
- 1 marker pen
- 24 hours
- Begin by digging a six-inch hole in your garden. Fill 1/3 of your jar with earth, then add water almost to the top.
- Shake the jar for 5 minutes, or until the earth has fully dissolved in the water.
- Leave the jar for one minute, then use a marker pen to draw a line on the jar where the first layer of sediment has settled – this is sand.
- Leave for a further five minutes then make another line where the next layer of sediments has settled – this is silt.
- Leave for 24 hours then mark another line where the sediments have settled – this is clay.
- Measure the distance between these lines to learn the different layers of sediment, then calculate what percentage of your earth is clay, sand or silt – this part is easier with a jar that has straight sides. The best soil is approximately: 40% sand, 40% silt and 20% clay.
To find out if your garden is acidic or alkaline, you can:
- Combine 2 tablespoons of earth with ½ cup vinegar in a bowl. If it fizzes, it’s alkaline.
- Place 2 tablespoons of earth in a bowl that has been moistened with cooled kettle water. Then, pour ½ cup of baking soda over the top. If it fizzes, it’s acidic.
- If your soil doesn’t react to either test, it has a neutral pH7 which is ideal for growing most plants.
Paid soil test
In exchange for a sample, some companies will tell you what soil type, or soil profile, your garden contains – plus any nutritional deficiencies. Popular UK tests include:
Readymade soil tester kits
Specialist soil test
Bridgewater garden supplies will give a detailed breakdown of your earth for £30
How to improve the pH of your soil
If you have highly acidic or alkaline earth and wish to diversify your garden with new plant species, you may wish to raise or lower its pH. As a general rule, a neutral pH7 earth is ideal for most plants, insects and earthworms. Remember, once your ground has been amended, it will not stay that way forever. Ideally, retest it every two months to fully understand its natural cycle and learn when to amend with your preferred substance.
Acidic soil
If your soil is too acidic and you wish to raise its pH add powdered limestone, also known as lime for soil. The best time of year to do this, is three months before your growing season. And, depending how large your garden is, you may choose to apply lime by hand and then rake it into the surface, or use a spreader before watering it in. Wood ashes will also increase the pH.
Alkaline soil
If your soil is too alkaline and you wish to lower the pH, add aluminium sulphate. Again, add it to the surface, then rake into the ground. Try to avoid doing this while plants are in the ground as sulphur can burn the leaves. If this does happen, wash the leaves with your hosepipe.
The best plant soil for…
The best soil for indoor plants and outdoor container gardens
Potting soil is best for indoor and outdoor plant pots or container gardens. You can buy a readymade promix like Miracle-Gro Potting Soil, Happy Frog Organic Potting Soil or Lowes Potting Soil, or you can make your own by combining two parts garden earth or topsoil with one part compost. If you wish, you can also add a handful of coir or leaf mold.
The best soil for raised garden beds
The best raised bed soil is a mix of 5% perlite, 35% compost and 60% topsoil. This guarantees nutrients, good drainage and long-lasting water retention.
The best soil for in-ground plots and vegetable gardens
Top-dress vegetable garden soil or in-ground plots with two inches of well-rotted compost and a healthy mix of manure each year. You can also add nutrients back into the ground by growing crops on rotation – for example, peas fix nitrogen into the ground.
Top tips
Recycle your weeds
They’re annoying, they’re everywhere and they steal nutrients from your favourite plants – but did you know, you can recycle their goodness into a green health tonic for plants? Just drop the leaves of weeds into a bucket of water, leave for three days then pour onto your plants.
Smother weeds
If you don’t have the time to dig up thousands of weeds, or you plan to make a new bed where lots of weeds are, just smother them. You can use mulch, plastic sheeting, newspaper or cardboard – anything that prevents light from getting through to the ground below and stops plants from growing.
Check your plants before you buy
Before you buy a new plant, check to see what ground they prefer so you can prepare your garden correctly. And, if isn’t right, you can either amend it or place your plant it in a pot
Feed the ground, not your plants
The nutrients, bacteria and minerals in your soil feed plants, so don’t just spot-feed random areas of earth; feed your entire bed to encourage more life.
Frequently asked questions
What wood is safe to border a garden?
The best woods to use are sweet chestnut or fir. Where possible, try to avoid pallet wood as most gets treated with toxic chemicals – this is most dangerous when growing edible plants or vegetables.
What is loam and why is it so good for growing plants?
Loam is a neutral, rich soil with a healthy balance of silt, sand and clay – approximately 40:40:20 ratio. It is ideal for growing plants and flowers because it’s not too heavy, won’t get waterlogged and retains vital minerals.
What is the best succulent soil and cactus potting soil?
Succulents and cacti need quick-draining sandy earth. You can amend compost with coarse builder’s sand (not beach sand) or gravel.
What is alluvial soil?
Alluvial soil is highly fertile tilth deposited by overflowing waters like riverbeds, over floodplains.
How to start a garden or prepare a garden plot?
Decide where your plot will be, monitor how much sun it receives throughout the day (most plants require six hours of sun per day), and then learn what soil type you have. Next, plan your bed by pushing sticks into the earth and wrapping string around each stick. Then, decide if you will have a HugelKultur garden, also known as a no-dig garden, or a dig garden. With a HugelKulture garden, begin by smothering weeds with layers of mulch, like cardboard or newspaper, then adding compost and well-rotted manure. And with a dig-garden, remove any weeds or grass, then work compost or manure into the ground with a garden fork. Once you have your soil-test results, amend accordingly then add plants. Our free garden planner will also help you to plan your garden.
Where can I learn more about earth?
There are plenty of places to learn more about earth, the study of soil and review soil maps. Check out the British Geological Survey (BGS), the UK Soil Observatory and Soilscapes.
What is sustainable soil?
Sustainable soil ensures a long term yield without damaging the environment or your bank balance. To learn how to naturally enhance your earth, reread this article.
Rebecca is the face behind Urban Undergrowth. She became addicted to gardening before it became popular and started writing this blog as a way to share her learnings. After all, sharing is caring. When she’s not digging potatoes, carrying caterpillars or sprinkling cinnamon, she’s a copywriter, painter, vegan chef and Muay Thai fighter.
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