Sandy soil is great for good drainage

Determining your soil type with a Jar test

TL;DR : Well you’ve done your Jar Test, now all that’s left to do is to find out what your soil is trying to tell you! Is your soil sandy, silty, loamy? And what does this tell you about its qualities and its flaws?

So you’ve done the Jar Test with some soil from your garden and you are now ready to interpret the results. Here we go!

What difference does it make if you have sandy soil or silty soil?

Water absorption

One of the most significant dissimilarities between soil types is the way in which they absorb and hold water. And we all know this is a matter of capital importance in plant well-being. Capillary action is the primary force in spreading water horizontally and in a homogeneous manner through the soil.

Just in case we lost you there capillary action (sometimes also called capillarity, capillary motion, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. So basically this is a part of what makes water seep into your soil or just make puddles when it rains. 

Here is an example with a brick I took from the Wikipedia page on Capillary action:

Capillary flow in a brick works the same wayCapillary flow in bricks with different levels of sorptivity (capacity of the medium to absorb or desorb liquid by capillarity) and porosity. You can see how they each absorb different quantities of water.

Both gravity and capillary action influence vertical movement of water. In heavier and less refined soils, water is more likely to be absorbed vertically (which is good if you have an old orchard or large trees for example, basically any plants with deep root systems), but will not spread very far horizontally (which will make it harder for plants with shallow roots to fend for themselves). The opposite is true for soils made of thinner particles.

Water intake rate, water retention and drainage

Below you’ll find a table of the important elements for each type of soil. For each type of soil we will help you determine water intake rate, retention and drainage. The soil’s intake rate (basically how quickly it absorbs water) will help you discover things like how often you should water your plants.

Coarse, sandy soils absorb water much faster than silt or clay soils which have a very low intake rate. Soils made of thin particles retain moisture longer than coarser grained soils do. If you supply water too often to a soil with low intake rate and a bad drainage power your actions will cause runoff, erosion or soil puddling, all of which waste the precious resource that is water and can cause damage. They may leave your plants roots exposed to the sun and this is not something you want.

Then comes retention. Soils that have bad water retention will need watering much more frequently. On the upside you will have less chances of root rot in the wet seasons or in winter. Most plants require a pretty good drainage because their roots don’t like to be left sitting in water.

Before that lets take a look at the results you got from your Jar test. Once you have counted the approximate proportions of each type of soil : clay, sand and silt (in percentage of course), here is a chart that will help determine your soil type.

How much sand, clay and silt do you have in your soil?Well now you have it, here is your soil type!

One last thing, watering your soil too often may lead to plants getting “lazy”. I mean, if you had a constant supply of water at your desk or your bedside table would you ever go to the kitchen to fill up? Well plants behave the same way. If the top soil is constantly moist the plant’s roots will not dig in as deep as they would if the have dry spells once in a while.

This may lead to your plants suffering damaged if you ever forget to water them. Watering plants abundantly every so often and then leaving them to dig deeper for water will make them more resistant to drought. Of course your soil needs to be aerated enough for the roots to form easily so try not to compact it too much.

Adding a bit of mulch, dead leaves or straw will help the soil to keep most of its moisture. This is something we often see recommended in permaculture.

Mulch : dead leaves, wood chips, straw, ... anything will do. These will not only keep the moisture in, the will also protect your soil, encourage soil life and feed your plants as they decompose.

Soil types

Here is a general table of the strong points and the weak points of of general soil type.

Sand offers great water intake but a very low water retention, which is why it is a good idea to mix it in with silt and clay! Each of these has their advantages and disadvantages, learn how to make use of them for the best gardening experience.

Soil type Soil texture Soil components Intake rate Water retention Drainage / erosion
Sandy soil Coarse texture Sand Very high Very low Low erosion
Loamy sand High Low Good drainage
Loamy soil Moderately coarse Sandy loam Moderately high Moderately low Low erosion
Fine loam Moderately high Moderately low Good drainage
Medium texture Very fine loam Medium Moderately high Moderate drainage
Loam Medium Moderately high Moderate drainage
Silty loam Medium Moderately high Moderate drainage
Silt Medium Moderately high Moderate drainage
Moderately fine Clay loam Moderately low High Moderate to low drainage
Sandy clay loam Moderately low High Moderate to low drainage
Silty clay loam Moderately low High Moderate to low drainage
Clay soil Fine texture Sandy clay Low High Drainage
Silty clay Low High Severe erosion
Clay Low High Very slow drainage

So which soil should you favor?

Some soils like loam or silt loam, are great for growing most types of plants. This is the kind of soil you should be looking for to grow the largest majority of your plants. But if you’re looking to dig a pond in your garden you should be looking for clay soil to keep the water in!

Thanks to this chart and your Jar Test, you should now be able to identify the base type of your soil. Yet there is much more to know about soil. In your garden you are very likely to have soil mixed in with rocks, gravel, chalk or even organic material. These materials are an integral part of what makes up your soil! So in your garden there may be many more elements including rocks and gravel (you know the things you took out before performing this test), but also organic material (cumulose) or peat, chalk, muck, … You may even have added part of this material yourself. Once you take your base soil and add all these different components to it your soil transforms into what is called a soil aggregate.

Soil aggregates

The addition of organic matter, water, gases and time causes the soil of a certain texture to develop into a larger soil structure called an aggregate. This is what you get in your garden. At this point it can be said to be developed soil. Knowing what elements you have in your soil allows you to know it better.

There are other elements that make it possible to rank soil these include color or consistency for example. We will talk about these later, you already have a lot of information to take in!

The best type of soil for traditional gardening : Loam

Loam is usually considered hands-down the best all-around soil for gardening. Almost any type of plant can be grown in loam without any making major modifications or additions to the soil.

Loam is great for several reasons. It holds its shape when squeezed or compressed and crumbles only slightly under pressure, which means that loam isn’t overly dense or loose.

Most loam is made from fairly equal parts of silt, sand and clay, giving it all the best qualities of each of these materials with few of the drawbacks.

  • The sand keeps the loam aerated so air, moisture and sunlight can reach the plants and the roots can develop without requiring too much effort from the plant.
  • On the other hand the clay and silt in the soil limit drainage and evaporation, keeping water and nutrients in place and making them easily available to plants.

Loam is great for a few other reasons. For example it warms up early in the spring, won’t be as likely to dry out in the summer (especially if you add mulch) and still drains well in heavy rain (you’ll end up with much less puddles), making it the perfect soil for year-round planting.

Different types of soils for other uses

Of course you may need soils for different purposes (filling a pond, fertilizing a plant, …) so just because people usually say that loam is the best soil, does not necessarily apply to your case. Different plants need different types of soils. Some plants love to have their roots in very humid clay soil whilst others will rot in these conditions.

Here are some of the things that your type of soil will influence in your garden. This table will help you decide where you want each soil type!

Generalized influence of soil texture separates on some properties / behaviors of soil
Property / behavior Sand Silt Clay
Water-holding capacity Low Medium to high High
Aeration Good Medium Poor
Drainage rate High Slow to medium Very slow
Soil organic matter level Low Medium to high Medium to high
Decomposition of organic matter Quick Moderate Slow
Warm-up in spring Quick Moderate Slow
Compactability Low Medium High
Susceptibility to wind erosion Moderate to high (if the particles are very thin) High Low
Susceptibility to water erosion Low (unless the particles are very thin) High Low if aggregated (if not high)
Shrink / swell potential Very low Low Moderate to very high
Sealing of ponds, dams, and landfills Poor Poor Good
Suitability for tillage after rain Good Medium Poor
Pollutant leaching potential High Medium Low (unless cracked)
Ability to store plant nutrients Poor Medium to high High
Resistance to pH alterations Low Medium High

If you want to know more about soil aggregates, you should read our next article on soil that will definitely be about this subject!

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