7 Common Mistakes In A Polytunnel

mistakes in a polytunnel

With so many tasks to plan, tarting gardening and growing in a polytunnel can be a bit scary at first. In this part of the Krosagro guide, we will talk about the 7 most common mistakes for crops under cover and we will present solutions to avoid them.


Mistake 1: Premature planting

Although the foil tunnel protects plants from frost, it is only partially. The cover allows the sun’s rays in, heating up air and soil. It also slows down the loss of heat throughout the day and night, and during sunny but cold days. Moreover, even without additional heating, in the form of a stove, ventilation or heaters for low temperatures, the greenhouse will be warmer. But it might not be sufficient, especially for exotic or oriental plants, while native plants should cope.


It is necessary to closely monitor weather and temperature in the tunnel, as well as respect the sowing dates so that the plants avail of comfortable conditions. This guarantee that seeds sown directly into the ground will survive the emergence, then grow properly. Whether it is a question of time or not having the opportunity to invest in heating, you can set up a mini polytunnel over the crops. It’s a small structure. It works just like a full-sized one, except that it is to be placed under a standard one.

Mistake 2: Planting too dense

It is understandable that every gardener aims to harvest as much as possible. But it must be remembered that every plant needs space for proper growth. Some of the plants, like spinach, rocket and lettuce, have no problems developing alongside others. However, a large part of them prefer more space, and neighboring crops can harm them. Tomatoes, often grown under cover, are one of those. They even require ventilation, otherwise they may fade. Other vegetables like broccoli, cauliflower, eggplant or pepper also need “breathing”space for development.


Before planning your modern garden in a polytunnel, try to draw it beforehand. It is worth getting acquainted with plants that you plan to cultivate, their breeding methods, minimum and maximum spacing, requirements for temperature, soil and fertilizers, and last but not least, their connections with other vegetables. Some of the plants can be planted close to each other, it works advantageously for both species, while others can fight each other. Plant association can help you in this matter.

As for air circulation under cover, the solution is to open the door or lift the openings. The first method is used in single-vegetation tunnels, the second one only in greenhouses with side ventilation.

Mistake 3: Watering too much or too little

Water is one of the most important raw materials needed for plant development. Watering, on the other hand, is the most frequent duty performed in relation with crop care. A hobby greenhouse, as the name suggests, is designed for users with a passion for gardening. Therefore, if not operating with a professional foil tunnel, it is difficult to precisely determine the amounts of water. A lot of people manage this task”by rule of thumb”. It is worth remembering that it is not the amount of water that counts but its distribution per square meter.

Over time, when plants feel excess or lack of water, changes can be noticed in them. Lack of water leads to dried up leafs and sunburns. While too much water can result in the appearance of fungi and mold.


Soil moisture depends on many factors : structure, pH, groundwater content and atmospheric factors outside the facility. And these are just a few reasons affecting water supply. If you want to have optimal growing conditions, you should purchase a moisture meter. The cost is limited. And the benefits coming from this device will save a lot of stress, and in particular avoid production losses.

It is very important not to pour water directly on the plants but at the base. The closer the root, the better. Sometimes tunnels are equipped with automated irrigation systems. Their cost is getting smaller with time and are not associated with professional foil tunnels anymore. The price depends on how efficient the layout has to be, but it is worth checking offers in online stores. DIY enthusiasts come up with great systems, and dozens of solutions are available on the internet.

Mistake 4: Bad positioning

Most vegetables and herbs need at least six hours of direct sunlight. Of course, there is quite a large group that has higher requirements, while others prefer shady positions. Therefore, even at the stage of planning a vegetable garden, you need to take into account the site and the level of sun exposure that is needed for proper growth.


A foil tunnel is not only a solution for heat and photophilous plants. After proper modifications, using a different cover or embedding it so that only the dome protrudes, it can fulfill a different function. A galvanized steel construction is very versatile. It can be used for mushrooms growing or plants requiring high humidity and low access to light. The only thing that will change is the cover on greenhouse frame.

Mistake 5: Poor soil condition

The key to success in growing vegetables and fruit under cover is to obtain a soil is full of nutrients. Food plants take the necessary ingredients from the soil and then transform them into a green mass. It is from these elements that flowers develop, giving later fruits. Spices, although they have a different growth pattern, have similar requirements regarding the ground.

Soil also has a structure, pH and reaction property which deteriorates over time. Sometimes, gardeners must adapt to certain criteria so that the crop avail of favorable conditions. This can be obtained with ecological means of compost or manure, and other agrotechnical measures to fertilize the substrate.


Fertilization is a regular activity with the aim to feed the soil. Any substrate, containing extensive humus, nutrients and proper structure, has a direct impact on the quality of the crop. Which treatments and when to operate them depend on the type of crop. At the end of the season, it is important that the land does not suffer from disease and still contains micro and macro elements.

Mistake 6: Growth of weeds

Even in the foil tunnel, weeds develop, whether they have been left in the ground when digging or have been introduced through clothes, shoe soles, etc. How they made their way in is irrelevant, but it is important to remove them immediately after spotting them. Systematic weeding slows their development. You have to remember that they multiply much faster than the main crop. They constantly “steal” nutrients, to finally spread hundreds of seeds. Therefore, allowing them to develop once is a guarantee of a long struggle with them.


Systematic manual, mechanical or chemical removal (avoid this last method when growing plants for domestic consumption). However, it is best to cover the substrate with agrotextile or mulch mats. Remember, even though the material limits their development, they will still manage to grow in unprotected places. With a limited space, however, you will not have to fly around the greenhouse in search of weeds.

Mistake 7: Big amounts of everything

How much you grow should depend on how much you can eat, process and eventually sell. You have to take into account that the more plants you produce under cover, the more care will be required. At the start of an adventure with gardening, enthusiasm can overcome anyone. You imagine a greenhouse full of vegetables, fruits and herbs. Unfortunately, you still need some practice, and that will come over time. Hobby gardening is not meant to be a long and constant struggle with yourself. Gardening should be enjoyed, entertaining, and give you a lot of satisfaction.


It is easy to lose control over vegetables and herbs. The idea of harvests and baskets full of delicious, fresh products can tempt you to plant crops that your family does not even like. For example, if your children do not eat green beans, use the garden space to grow vegetables that everyone can appreciate. There is no reason to grow the full range of a seed catalog. If you really only need tomatoes, lettuce and peppers, and more importantly, only two or three of those per week, do not overdo it. In addition, having so many vegetables growing at once requires time and energy. This means less focus on weeding, watering and other duties.


As the old adage says, “It’s only those who do nothing that make no mistakes”. Well, you can prevent many mistakes in a polytunnel by knowing what to avoid. A polytunnel, like a garden, is a place where dozens of processes take place, some affecting others, with intricate connections occurring between them. Disturbing one of them can lead to chaos and even interruption of plant growth. Some are easy to correct, and the consequences are minor, while others may lead to the death of plants in extreme cases.

Don’t worry! Even experienced gardeners with many seasons under their belt make mistakes. However, from one year to the next, the yield will increase. The pantry will get filled up to the brim, and you will then reflect with a smile on your first jobs in the greenhouse.

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