When preparing a vegetable bed, it’s important to know what kind of soil you’re working with. The make-up of your soil can have knock-on effects on what kind of plants you want to grow, as well as how much you’ll have to irrigate or add fertilisers. By testing your soil you can avoid such gardening pitfalls as overwatering and waterlogged soil. It can also help you decide what kind of fertiliser or soil amendment to use.
If your soil test results come back with suboptimal results, you need not get discouraged. With most soil types there are all kinds of weapons at your disposal for rebalancing the make-up of the soil and turning it into a more suitable medium for growing plants in.
Types of Soil
Each type of soil will have its own physical make-up, challenges, strengths and weaknesses. When you know what soil type you’re working with, you can be more mindful of plant and watering requirements.
Clay - Clay soil is pretty dense. It can get very sticky and is prone to compaction when wet. Clay soil has a high nutrient content, but you need to ‘unlock’ the nutrients by adding organic matter or horticultural grit. This type of soil has very good water retention but, alas, it won’t drain very well. In dry weather the soil can also crack, leading to water runoff.
Silty - Silty soils have a lighter and grainier texture. They are good at retaining moisture and are fertile, but can become compacted when walked on.
Sandy - Sandy soil is composed of large particles and has a coarse, lighter texture. It drains very well but tends to have poor moisture retention. This can be mitigated by adding organic matter that will bind the particles together better. It’s an easy soil to work with and cultivate, while another advantage is that it will warm up quicker in spring. However, nutrients tend to wash out of sandy soil faster.
Loamy - This is the one that most gardeners will be hoping for. Loamy soil has a nice mixture of clay, silt and sand, with a healthy balance of nutrients and drainage that’s right in the sweet spot.
Soil Testing
While soil can be sent away for a laboratory for the most accurate and detailed tests, there are a number of DIY soil tests and testing kits available to the home-grower. These can range from simple thermometers or pH strips to more comprehensive kits using test tubes and chemical reagents.
Soil pH Testing
Before getting started on a vegetable bed you should ideally have a fair idea of what the pH level of your soil is. pH is a scale that goes from 14 to 0, and indicates that a soil is either acid or alkaline. A reading of 7 means that the soil is neutral; as you go above 7 the soil is becoming more alkaline and as you go below 7 it is becoming more acidic. Most plants will do very well in a mildly acidic soil (6.0 to 6.5). A pH level of between 6 and 7.5 is also where beneficial microorganisms will be at their most active, spreading nutrients to roots and breaking down organic material.
Acid Soil
If soil is too acidic or is reading below 6, the best thing to do is add alkaline material: ground limestone is commonly used for this purpose. When applied to the soil you should give it time to slowly work its way in before planting. If acid soil drops below 5.0, this can start affecting nutrient availability. Alternatively, it can lead to manganese or aluminium toxicity. Overly acidic soil is not a good environment for microorganisms or beneficial bacteria: at levels below 5.0 this activity can halt altogether; this in turn can lead to a breakdown in soil structure.
Alkaline Soil
With high pH levels in the soil phosphorus availability will decrease, iron chlorosis can strike plants and many nutrients will be less accessible. Alkaline soil does have some advantages: the brassica disease ‘clubroot’ is much less likely to take hold for one. As you may have guessed, adding acidic materials (such as pine needles, shredded leaves and composted kitchen waste) can make it less alkaline and balance it out a bit more. However, very alkaline soils can be problematic and there may not be a whole lot you can do to make it workable. Fortunately, the general climate in Ireland and the UK means that neutral or slightly acid soils are common. Alkaline soil can often be found in areas with open chalk hills.
Soil Moisture Kits can measure moisture levels at the roots. Most commonly the test consists of a simple probe that you can stick into the soil. Knowing the level of moisture in the soil helps the gardener to judge when or how often plants should be watered. It can also cause you to be more prepared for any disease or pests that tend to favour overly wet or dry soils.
Soil Thermometers can measure the temperature of the soil. They can be used when planting out in spring, to make sure that the soil is warm enough for sowing seeds or seedlings. Thermometers can also be used in the polytunnel, greenhouse or with propagators, warning you when temperatures are getting high enough for plants to be susceptible to heat stress and damage.
When To Test
For best accuracy, it’s recommended that you don’t test the soil within 3 months of applying fertilisers, compost or soil amendments. Recent spells of hot or wet weather can also influence the results. It’s best to take a number of samples from different areas of the garden.