What sort of soil do you have?

Soil is made up of three main things:

1. minerals (rocks, sand, clay, chalk etc.)
2. organic matter (this means the remains of plants and animals - but when this post talks about adding organic matter, it mainly means decayed vegetable matter like compost or the manure of herbivorous animals such as horses, rabbits and guinea pigs)
3. living organisms that live in it (worms, insects, micro-organisms and even my mortal enemy, the slug).

What sort of soil you have largely depends on the mineral components in the soil. The main types are: clay, sandy, silt, loamy, chalky or lime-rich and peat soils. This last one isn't actually so much based on a mineral as on the organic matter - peat - but all the rest are characterised by the key minerals in them. Practically no one has peat soil in their garden (and presumably if you do, you live near a peat bog and know all about peat), so I'm mainly going to ignore that one.

If you live in the UK, you can find out what your soil's likely to be using this map: http://www.landis.org.uk/soilscapes/

According to the map, my soil is likely to be loamy. I say "likely to be" because my gardening course said soils could vary even across a single garden.

If you don't live in the UK or want to double check whether what the map says makes sense for what you're seeing, here are two questions to help you easily identify if you have a strongly chalky or clay soil followed by some other questions if the answer turns out not to be obviously one of those:

1. Does it have pieces of chalk in it? They're white and you can easily use them to draw a line on other stones (just like the sticks of chalk you can buy for a blackboard). If so, you have chalky soil.

2. Does your soil act a lot like potters clay? It's dense, sticky or slimy and like moist clay, and hard to dig when it's been raining and very hard, cracked and dry clay-like and hard to dig when there's been no rain for ages, particularly when it's been hot. When it's moist, you can shape it and it stays that way, a bit like you can with pure clay. (You can possibly tell I once had a bad experience trying to help a friend dig his clay soil garden, it was much harder than I was used to).

Once you've got past those simple questions which show if your soil has a lot of obvious chalk or clay, things get a little more complicated. The first thing to do is feel your soil between your fingers.

How does the soil feel?

sticky and heavy (like moist clay)	clay soil
slimy	clay soil
gritty and light (a bit like sand on a beach, but often not sandy in colour)	sandy soil
friable = easily crumbled	loamy soil (or in my experience, can also be sandy, as sandy soil sometimes seems as friable as it does gritty)
slightly soapy, slippery	silt soil (pure silt soils are rare in gardens)

If the answer is obvious, you can stop there, if not, ask:

What does the soil look like in the jam jar test?

Put about a tablespoon or two of soil in the bottom of an empty jam jar (no need to use a tablespoon, that's just a guide to the rough amount you're aiming for). Fill it up with water, give it a good shake, then leave it for an hour. After an hour, the organic parts of the soil should be floating on the surface. The question is what's happened to the rest:

white bits floating in the water	chalky soil
water might look a bit murky, but thin and the soil has sunk to the bottom; if you try and get the wet soil to stick together it either won't stick together at all or has difficulty sticking together, it feels a bit gritty	sandy soil
the water either has bits of clay floating in it or is no longer transparent, but has formed an emulsion with the clay or both, any soil at the bottom doesn't feel gritty and can be clumped together into a ball that stays together quite well	clay soil
like clay, but what's left at the bottom of the jar feels gritty	loamy soil, which is a mixture of clay, sand and silt

Soil from my garden  (loamy according to Soilscape) one hour after I shook the jar. No sign of chalk and not seeing much sign of clay.

Soil from the garden of some friends in Guildford. Soilscape, says it's loamy and clayey, but actually unfortunately it doesn't look very different from mine in the jar test (especially after you factor in different lighting and whether I'd left it as long). Not sure if that's because mine's also a loamy soil and as such also contains some clay or if the slight difference in the water is significant and shows theirs has more clay. Theirs definitely also contains sand or similar particulate matter, I found traces of it when I was cleaning the jar out, so this seems to back up Soilscape's assertion that their soil is loamy as well as clayey.

What happens if you try to roll a sausage out of your soil when it's moist?

rolls into a completely uncracked sausage, shiny when rubbed	high clay content
rolls into a completely uncracked sausage and is a bit sticky, but not shiny when rubbed	clay soil, but lower clay content
won't roll into a sausage at all	no clay content
rolls into a cracked sausage, not sticky	I couldn't find a definitive answer on that. Possibly loamy soil. As far as I can make out, it's not a soil you'd refer to as a clay soil, but it may have some clay content.

Soil from my garden rolled up into the best ball I could manage when wet (I hadn't found the sausage test when I did this). This is probably indicative of the 20% clay content in loam, but it's not a dominant element because it's not in the least sticky.

Me finding particles in my soil - could be sand or silt or both, but definitely not pure clay

This all seems to back up Soilscape's view that I have a loamy soil.

What colour is the soil?

very pale/greyish, chalky coloured soil	chalk (not being this colour doesn't mean no chalk)
a bit orange or reddish	clay soil with a high clay content can look reddish or orangey (not being this colour doesn't mean no clay)
lighter coloured soil	probably contains less organic matter
darker coloured soil	probably contains more organic matter

My soil (not dark brown, but definitely not chalky or greyish either)

Well-rotted organic matter from the bottom of my compost heap

Clay soil

The good news: clay soils are very rich in nutrients. They are usually pH neutral (neither acidic nor alkaline), which means that their pH is 7. Most plants prefer pH 6.5-7, so they're good for most plants.

The bad news: they can get very cloddy and tend to be hard to dig whether they're wet or dry. They also hold a lot of water, which is sort of good because they need watering less often, but bad because they tend to get water-logged, which plants don't like. They also take longer to warm up in spring, which means effectively spring comes later for your plants. Also, they're easily damaged when water-logged, so don't dig them or walk on them till they've dried up a bit (although completely dry won't work either, as they can bake rock hard).

What to do to help: add plenty of organic matter. This will break the clay down into crumbs, which will make its nutrients more available to plants and also make the soil warmer, easier to work and less prone to compaction. Also, dig them in autumn or early winter when they're less wet to avoid damaging them. If you leave them in narrow ridges after digging, this could help drainage and encourage frost to help break them down instead of you digging. Adopting a no-dig regime may be better for the soil (and a lot less work for you) – I'll be talking more about no-dig systems in later posts, as my bad back means no-dig' could be really handy for me.

See here for more information and advice from the RHS.

Sandy soil

The good news: these are easy to dig and cultivate and generally to work. They warm up quickly, which effectively means spring comes earlier for your plants. They also tend not to get water-logged because they're free draining, so plants that like it dry (don't like soggy roots) will thrive. According to this article in the Telegraph, you may well be less troubled by slugs and snails than people with less freely draining soils.

The bad news: because they're so free draining, they lose water easily and need a lot of watering (hard work and/or bad for the environment). They're also naturally low on nutrients unless they contain plenty of organic matter. They can also be very acidic. Acidic soils are pH 6.9 and below, and most plants prefer pH 6.5-7, so lower than 6.5 will not suit quite a lot of plants.

What you can do to help: add plenty of organic matter, this will bind the loose sand into more fertile crumbs, stopping it from draining quite so quickly. It also adds nutrients and makes the nutrients more easily available to plants. Adding fertilisers can help provide the nutrients it's missing. Choose plants that can cope without much water and add a mulch to the top to preserve as much water as you can. Also, it may pay to pH test your soil, and stick to plants that do well in its level of acidity. I'm going to write more about soil pH in another post.

See here for more information and advice from the RHS.

Silt soil

The good news: these are fertile, fairly well drained and hold more moisture than sandy soil.

The bad news: these soils are made up of fine particles (even finer than sand) and can be easily compacted by treading and use of garden machinery. They are prone to washing away and to wind erosion if left exposed to the elements without plant cover.

What to do to help: add plenty of organic matter. This will bind the silt particles into more stable crumbs.

Loams

The good news: lucky you, these are considered to have a perfect balance of all soil particle types, they're 40% sand. 40% silt and 20% clay. This means they're fertile, well drained and easily worked.

The bad news: slugs seem very happy in loamy soil (they're certainly present in large numbers in my garden and this article in the Telegraph seems to imply that slugs are happy in soils that can retain moisture well). You may well have a lot of them.

What you can do to help: even though this soil type is great, the advice is that you should still regularly add organic matter. I assume this is to replenish nutrients your plants are using up. Also, according to the descriptions of different types of loamy soils on Soilscape's map, not all loamy soils are high in nutrients.

Chalky soil

The good news: some of Britain's most productive agricultural soils are chalky. They warm up quickly in spring and brassicas (plants including cabbage, cauliflower and broccoli) are less likely to get clubfoot. Light chalky soils rarely flood because they're free draining.

The bad news: because chalk soils are alkaline (i.e. they have a pH of 7.1 or more – the higher the pH the more alkaline it is) they won't support lime-hating plants or ericaceous plants that need acid soil conditions, and you can't acidify a chalk soil. A lot of chalky soils are shallow, i.e. if you dig down through the soil, you'll get through it and hit the layer of rock below quite quickly. They're also free-draining (i.e. need watering regularly) and low in nutrients, but where clay is present, nutrient levels might be higher and they might be able to retain more water. Organic matter often breaks down quickly in chalky soils.

What to do to help: Choose plants that will thrive in alkaline conditions (also known as calcioles or lime-loving plants). If you want to plant acid-loving plants or lime-hating plants (also known as calcifuges), plant them in a pot or a raised bed that you've filled with a suitable soil you've bought (with a raised bed if you just use acidic compost it will eventually sink away into your soil, so actually buy acidic soil rather than compost. That can't happen with a pot, so acidic compost should be fine). Add organic matter very frequently.

See the RHS's website for more information and tips on chalky soil.

Peat soil

The good news: they've usually very fertile and contain a high proportion of organic matter (peat). It warms up quickly in the spring. It's great for plant growth if fertiliser is added.

The bad news: highly water retentive, so may require drainage if the water table is neat the surface. Fewer nutrients because because the soil’s acidic nature inhibits decomposition or organic matter (which is a reason there's so much of it).

What to do to help: add fertiliser. Unlike the other soils, presumably adding organic matter doesn't help because it's already full of it.