Best Soil For Greenhouse Beds

how to select best soil for greenhouse beds

A greenhouse can help you grow plants out of season, or even plants that would not ordinarily grow in the weather conditions at the location of the greenhouse. It does this by retaining heat inside it, thus allowing plants that grow in hotter climates or weather conditions to continue thriving. One of the most important components of a greenhouse is the soil. In this article, we will focus on how to select a soil that is appropriate for your greenhouse.

The importance of having the right soil mix

best soil for greenhouse beds

Soil isn’t just dirt when it comes to plants. Not only does it support and anchor the plant as it grows, it also supplies the plant with water, nutrition, and oxygen, and sometimes the right microbes to facilitate the supply of the right nutrients to the roots. You might need to test the soil you currently have for its pH levels and the nutrients available in it. Remember, you need the right amount and the right pH – too much of a nutrient is also detrimental to plants. For example, too much nitrogen will give many more leaves but fewer flowers or fruit.

How to select the best soil for the greenhouse bed

There are many different types of soil, and the right soil for your crop will most probably be a combination of some of them. Let us go through some of them.

Sandy soil

Sand has the largest size of particles of all the soil types, which is also why it does not retain water or nutrients well. Carrots, radishes, potatoes, lettuce, tomatoes, corn, watermelon, and cucumber are some of the plants that grow well in sandy soil.

Silty soil

It has a particle size smaller than that of sandy soil, which is why it retains water and nutrients better. It is usually rich in nutrients, which is why most fruit and vegetable crops will grow well in silty soil. You merely have to make sure the drainage is done well.


Clay is made up less of organic matter and more of minerals and water. Crops whose roots do not grow deep will thrive in clay, thanks to its water retention. These include lettuce and snap beans. Broccoli, cabbage, and brussels sprouts also grow well in clay.


best greenhouse soil

Usually, the best type of soil to grow a crop in a greenhouse. It is a mix of all three types of soil mentioned above, and humus. ‘Humus’ is made of decayed leaves and animal matter, it helps the soil retain moisture and nutrients.

Loam, compost, and potting mix all put together in the ration 6:3:1 will serve you the best. If the original soil is not fertile, you can use equal parts compost and potting mix – but never let the amount of peat moss be more than a fifth of the total mix. It is too acidic for vegetables to grow properly.

How to test the soil you have

There are a few simple tests you can conduct to test the soil you have.

The first one is how to check the pH of the soil – how acidic or alkaline it is. You’ll need two bowls, four tablespoons of soil, some distilled water, and a half cup of vinegar and baking soda each. In each bowl, put two tablespoons of soil. In one, add the vinegar. If it bubbles, your soil is alkaline. In the other bowl, add some distilled water to the two tablespoons of soil, and then add the baking soda. Got bubbles? Your soil is acidic. You can adjust the pH toward neutral by adding ground limestone to acidic soil, or ground sulfur to alkaline soil.

best soil for greenhouse beds

You can also judge how much organic matter the ground has by the earthworms it has. If you have too few, adding organic matter like compost, mulch, and manure will help up the earthworm count as well as microbial activity, which will make more nutrients available to your plants.

If you want to be professional about testing your soil, you can always send it to a lab for testing. The results will help you decide not just what fertilizer to use, but how much to use as well.

How to adjust the properties of the soil you have

If the type of soil you have does not meet the requirements you have for the crop you have planned, there are a few things you can do to make it more suitable for the crop. Ground lime added to the soil will make it alkaline, and sulphur or aluminium sulphate will make it more acidic. If you need sandy soil to retain more water and nutrients, mix in compost and manure.

Mulch will also help, with the happy side effect of contributing more nutrients as the components of mulch (like dead leaves) break down.

Clay has the opposite problem as sandy soil – it retains too much water. So to improve its drainage, add large quantities of organic matter and peat. This will help aerate it as well.

Protecting the soil

Now that you’ve selected the right soil for your crop, you need to protect it. For example, before planting a crop, you need to conduct a nematode analysis of the soil. If there is a high amount of plant-parasitic nematodes, you need to reduce them by planting a crop of brassicas.

Preparing compost and adding it to the soil will offer many benefits as well, as the slow release of nutrients, better water retention (meaning less water used for irrigation), as well as making sure the soil is loose and aerated thanks to the right organic components like worms and insects.

Preparation of the soil is a different topic – common beginner mistakes include levelling the greenhouse by removing the nutrient-rich topsoil rather than levelling the sub-soil, not engineering the correct amount of soil drainage, and not doing a nematode analysis. However, by choosing the right soil and treating it, you can give your plants the best opportunity to grow and bear maximum yield.

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