Assessing Your Soil
From: DK Books - Herbs
Your yard and gardens will contain a variety of soil types at differing depths. These types fall into a number of textures, which very broadly are silt, sand, and clay. The proportional mixture of soil types, when combined with coarser material and organic matter, tell you how fertile and easy to work your garden soil is going to be. These combinations will also determine how well drained your soil is, which will help you decide when to cultivate your herbs. Soggy soil, for example, is not only much harder to work, but also results in compacted puddles.
As you dig deeper, the soil is likely to gradually change from the top humus or organic-rich layer through a heavier (or perhaps more sandy), compact layer, until you reach a layer in which it would be impossible to grow a herb. It is important not to bring any of this poorer subsoil to the surface as it may impair the fertility and texture of the topsoil, which can vary considerably in thickness, even within the confines of a small garden.
This important test measures the alkalinity or acidity of your soil on a scale from 1 (acid) to 14 (alkaline) and so helps indicate what types of plant can or can’t thrive in your garden. Cheap testing kits are reasonably reliable and readily available with almost instant results if the instructions are closely followed. Try to take a number of samples, as many gardens vary from one end to the other. Remember, too, that most herbs happily grow in the range 5.5 to 7.5 and if your test results are consistently outside this range, it would be well worth seeking a second opinion or engaging some professional advice before attempting to remedy the situation.
Test Your Soil
If you are planning a new herb bed or taking on a new patch for the first time, it is important to find out more than just the soil pH. Dig a hole about 8 in (20 cm) square and to a shovel's depth — it is well worth digging at least one hole every 15–30 ft (5–10 m). Pause to inspect the soil you are excavating. If it is dry and dusty, it is likely that you will need to add moisture-retentive organic matter, or if it is sticky or slimy, extra drainage will be a priority. Small stones and gravel shouldn’t be a problem as long as there is an equal amount of soil, but large rocks will need to be removed. On new-build or recently renovated sites there may be a thick layer of rubble or clay not far below the surface, which would need to be dug out and removed.
When you have finished digging, leave the holes for 24 hours (cover them with a board to protect from rain or trapping wildlife) and then check for any water in the bottom. If there is only a little water or the hole is mostly dry, nothing needs to be done; but if it is half full or more, the site drainage may need improving. This can be quite an extensive project as it may entail installing pipes or gravel-lined drainage channels to a deep water sump or pond. Your sample hole may fill up with water as you are digging it, which could indicate a high water table and poor drainage. This may just be a temporary or seasonal result, but it does mean the site is not ideal for most herbs, although raised beds may work.
Fill Up With Water
For more information about your soil, fill the hole with water, using either a hose or bucket (pour gently as the sides of the hole can collapse). The speed at which the water drains away will give further indications of the suitability of your ground for herbs and the additives that could be included when cultivating to improve the structure and texture of the soil. More radical drainage solutions may be needed if the water is still sitting there the next day, but this could just be a localized problem — try digging another inspection hole 3 ft (1 m) away and testing again. On very well-drained sites it can be difficult to fill the hole as the water may dissipate as quickly as it is poured in. This need not be a problem, however, as many herbs like this type of soil.
Scrape Soil Away From Sides
Once the water has substantially drained away, carefully scrape the sides of the hole with a trowel. The layer most recently in contact with the water will be damp and dark and the extent to which the water has seeped sideways should be clear.
If this horizontal seepage is small, it is possible that the soil is over compacted and simple cultivation may relieve the problem. Additional sand and organic matter added together with rotted compost or manure will also help your soil absorb and store moisture without becoming waterlogged.