Should you test your soil before growing vegetables?

Most people who grow vegetables in their garden never test the soil, and for most gardens that is probably fine. But if your plot has an uncertain history, if it was previously industrial land, or if it is on a street where lead paint and leaded petrol have been accumulating in the topsoil for decades, a basic screen is a reasonable precaution before you start growing food.

Which contaminants are most relevant for residential gardens ¶

Lead is the most commonly elevated contaminant in urban residential soils. It accumulates from decades of leaded petrol, lead paint on older buildings, and in some areas from historical industrial activity. It does not break down. A garden that has been a garden for fifty years in an urban area may have lead levels that are worth knowing about, particularly if children play there or if you are growing root vegetables.

Arsenic occurs naturally in some Japanese soils, particularly in areas with certain geological backgrounds, but it can also be elevated near former orchards where arsenical pesticides were used historically. Cadmium is relevant near former smelting or mining areas. Total petroleum hydrocarbons are the parameter to check if the land was ever used for vehicle storage, fuel storage, or light industrial purposes.

What the soil guideline values mean ¶

Japan's Soil Contamination Countermeasures Act sets soil environmental standards, which serve the same role as soil guideline values (SGVs), for a range of contaminants. These are not absolute safe/unsafe thresholds; they are risk-based screening values calculated for specific land uses. The SGV for lead under a residential garden with plant uptake is lower than the SGV for the same land used as a car park, because the exposure pathways are different.

When Lank CoreLab reports soil results, we compare them against the SGV for the land use you have described. A result above the SGV does not mean the land is unusable; it means the exposure pathway needs to be considered. Raised beds with imported topsoil, for example, are a practical and widely used response to moderately elevated metals in urban garden soils.

How to collect a representative sample ¶

A single core from one corner of the garden is rarely representative. For a residential garden screen, we recommend a composite sample made up of five to ten sub-samples taken from across the plot at the depth you are growing in, typically the top 30 cm. Mix the sub-samples together, take approximately 200g from the mixture, and seal it in a clean bag. Avoid sampling immediately after heavy rain or fertiliser application.

The residential garden soil screen costs ¥15,500 and covers the parameters most relevant to vegetable growing and children's play areas. If your garden has a more complex history, get in touch with us and we can advise on a more targeted panel.