Whether you are an owner of a hobby 6 x 8 ft greenhouse or a commercial polytunnel, good soil is a key to successful growing. Many growers sit a greenhouse on the existing soil. It helps to save on the overall costs of building a greenhouse. At the same time greenhouse foundation supports the whole structure.
Nevertheless if you sit greenhouse on the existing ground or build a foundation, you need to prepare the greenhouse soil for planting. However, the existing soil might not be the best option, especially if it is dry and old. In this case, it can be helpful to decide what are you mainly going to use your greenhouse for.
One option is to have an ornamental greenhouse, meaning that you are not going to grow Tomatoes or other vegetables and fruits. That way you can use the entire space within the structure for pot plants. For example, you can keep flowering plants like Impatiens, Plumbago, Iresine, Hypoestes, Streptocarpus, Begonia.
On the other hand, you can have a productive greenhouse. Use all available space to grow vegetables and fruits in either pots, growing bags and raised beds.
If you want to grow fruits and keep pots with ornamental plants at the same time, you can organize a mixed greenhouse. For example, you can grow grapes with the vines secured along the ridge whilst Pelargonium and Fuchsia pots placed on the benches.
What is the best layout inside greenhouse?
The traditional layout is to have both sides of the greenhouse floor for growing plants and central path made of concrete slabs or covered with gravel. It is important to have that central path in the middle of greenhouse.
First, that is where you are going to walk when watering plants. Second, you can use this area for a work bench. Last but not least, it helps with the drainage. I would not recommend relying on rammed ground and would advise to lay concrete slabs on sand.
Greenhouse Soil Preparation
Step 1 – Identify the type of soil in your garden.
What types of soil are there?
- Sandy soil – this type is mainly made of sand particles which don’t hold nutrients very well.
- Silt soil – this soil is mixed with rock and mineral particles that are larger than clay but smaller than sand.
- Clay soil – clay is comprised of minerals and water so clay soil tends to have more mineral compounds rather than organic matter. You are likely to have clay soil in your garden if it resembles a brick with cracks when dry and looks like putty when its raining.
- Loam soil – this soil is a mix of sand, silt, clay and humus. Humus is dark, organic element of soil that is made of decayed leaves and animal matter. Humus makes the soil to retain moisture and nutrients. That is the best type of soil for growing plants.
So, what is the best soil for a greenhouse?
A mix of loam soil with compost and potting mix is the best soil for plant growth in greenhouse. Prepare the mix using 60% loam soil, 30% compost and 10% potting mix (peat moss, perlite and/or vermiculite). If the quality of your native soil is poor, you can mix half potting mix and half compost. However, make sure that the total amount of peat moss doesn’t go over 20%. It is naturally acidic and can be damaging for growing vegetables.
Step 2 – Prepare the greenhouse soil for planting.
If loam soil covers the majority of the ground in your garden where you plan to sit your greenhouse, you can plant on it. You can use garden fertilizer, just dig it in to produce nutrient rich soil. Also, I would suggest adding a liberal amount of garden compost especially before planting.
Do not plant the same crop in the same spot and in the same soil year after year. Soil can build up diseases and pests, so change the soil annually and replant your crops.
Many gardeners switch from growing in one or both sides of the greenhouse floor soil to planting in growing bags and pots. Alternatively, you can build raised beds inside your greenhouse and fill them with half potting soil mix and half garden soil.
Types of Commercial Bagged soil
There are four types of bagged soil you can buy:
- Topsoil – the primary use of topsoil is to fill in the holes in the lawn. Usually topsoil consists of reed sedge peat moss and sand. It can loosen heavy clay soil and increase moisture retention in light soil. You should not be using topsoil for gardening.
- Garden Soil – it is a premix of organic matter and fertilizer. You can use garden soil to mix with the native soil in your garden to improve soil structure, adjust pH and add nutrients. It is for in-ground use only and is perfect for planting.
- Raised Bed Soil – as raised bed is an enclosed container, the structure of garden soil or native soil on their own is too dense and is not suitable. Raised beds needs proper aeration and drainage. That is why you need to use a mix of half potting mix and half garden soil.
- Potting Mix – there are different variations from compressed coir and plant food or organic matter with earthworm castings and organic bat guano enriched with microbes and fungi. Most of the time you can just fill the pots with the potting mix straight from the bag. It allows adequate drainage, airflow and room for roots to grow.
Please let me know what soil are you using in your greenhouses and what layout works best for you.
Happy Growing!
