Why you should know the temperature of your soil

By | 11/05/2016
A Soil Thermometer

As spring gradually eases its way in, the days slowly become longer and the sun rises higher, how do you know when to start repairing or re-seeding your lawn? The easiest way by far is through knowing the temperature of the soil.

A simple soil thermometer can be purchased in any reputable garden centre. It is a reliable way to improve the success of sowing grass seed.

The reason for this is simple. In the grand scale of gardening, grass is not a fussy plant. It only requires three things to successfully germinate from seed. These are temperature, moisture and contact with the soil.

The contact with the soil we can control by sowing the seed correctly and preparing the lawn thoroughly. The moisture we also have some control over by sowing the seed during a traditionally wet time of year (autumn or early spring) or watering the seed if it hasn’t rained for a while. However nature is certainly in control when it comes to the temperature of the soil.

Most grass seed requires a temperature of at least 8 degrees Celsius in the soil for it to “activate” and begin to grow. Below this temperature it will just lay dormant and wait until the temperature rises. However, it then runs the risk of becoming food for birds, mice or any other small creatures looking for an easy meal. If they sit for too long the seeds may rot and die altogether.

If you are planning on seeding in the autumn, knowing the temperature of your soil will help you to know whether or not it is too late to start your lawn regeneration.

Some specialist grass seed will germinate at slightly lower temperatures. It will be slow and can be a little more expensive than the usual lawn seed varieties. Generally it’s worth just waiting until the soil has warmed.

Additional benefits of measuring the soil temperature

Using an infra red soil thermometer to check soil temperature
Using an infra red thermometer to check soil temperature

Over half of a grass plant is in the form of roots buried in the soil. The speed in which the grass grows (called the metabolic rate of the plant) is directly related to the temperature. A cooler soil, will slow the rate of growth of your grass, or even cause it to stop growing altogether which is why it doesn’t need cutting in winter. Warmer soil contains more energy so the grass will be able to use nutrients more readily and grow faster. This is a great way to judge when to start your mowing regime, as the soil temperature will be different from one year to the next.

Soil is a fantastic insulator and takes a long time to warm up or cool down. It “lags” behind the actual temperature of the air so it is just because it is a nice warm spring day, does not mean that the soil is warming enough to start seeding!

So grab yourself a simple soil thermometer to improve your success rate at sowing seeds all round the garden!

Kris Lord

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