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In unheated greenhouses, plants need to be protected from frost.
Wouldn’t it be easier to wait for stable warmth?
There is no clear answer: it all depends on what your priority goals are. To get a decent harvest, you will have to think through a protection strategy, choose an acceptable option and plant seedlings on time.
Plant seedlings at the optimal time
If you want to wait for stable warmth, that’s your choice, but keep in mind two nuances. Firstly, frosts can come even in June, and what to do with overgrown seedlings until then is a question. Secondly, the optimal planting age for each crop is not an empty phrase. Overgrown plants get sick longer, take root worse, and yield a harvest later. For example, our expert Vasily has repeatedly talked about an important feature of cucumber development: in the 6-leaf phase, their root system begins to actively grow, and by this time they should already be sitting in the garden bed. Otherwise, at best, the development of the plants will stop, at worst, they will die.
Ways to protect
Well, now let’s move on directly to the methods. I tried to collect as many as possible, but if I missed any accessible, labor-saving method or you have an interesting solution, be sure to tell us about them in the comments, okay?
Greenhouse
I like this method: it is not difficult to set up and take down the greenhouse, it does not take up much space in the shed when disassembled, and most importantly, it reliably protects the seedlings. Under a cover made of spunbond (60 g/m²) in a polycarbonate greenhouse, tomatoes and peppers survived frosts down to -5°C without losses.
Individual “fur coats”
There are many varieties, but the essence is the same – a personal shelter for each plant. Since we grow seedlings not individually, but in tens and hundreds of roots, we usually use budget materials at hand.
Plastic bottles: despite all my dislike for this material, I must admit that light, durable containers cope with the task perfectly. Under such a shelter, even in open ground, my cucumber seedlings withstood night frosts of up to -3°C, which lasted for a week!
Plastic bottles do a great job of this task.
Yes, I don’t like beds filled with plastic bottles, but if I had to choose between the aesthetic appearance of the shelter and preserving the seedlings, I would choose the latter without hesitation. In my opinion, this method has only one drawback: it will require a lot of space to store the alternative cloches.
glass jars: suitable for covering seedlings, since plants with real leaves are difficult to squeeze into a narrow neck. However, when there is nothing else at hand, and a drop in temperature is expected at night, the seedlings will have to endure. It is better to break a few leaves or even plants than to lose the entire batch.
It is problematic to cover grown seedlings with a jar
Tents made of newspapers and cardboard: paper is a good heat insulator, so it will definitely come in handy for protecting heat-loving crops. In terms of saving time, cardboard boxes are very convenient: you don’t have to make anything, just put them on the bed, and that’s it. Just in case, deepen them a little or sprinkle the bottom edge with earth, leaving no chance for cold air to get under the shelter.
Newspaper tents require a bit of fiddling, but nothing complicated. The author of the method recommends making them multi-layered, and to further enhance the insulating effect, crumple the newspapers well. The essence of impolite treatment of periodicals is clear: increasing the air gap between the sheets of paper. The tent itself is easy to make: roll a cone of the desired height and volume, fasten the edges with a stapler or tape (you can use both), place it over the plant and sprinkle the edges. In theory, I like the method and it seems promising, but how it will work in practice is unknown.
Hay and straw
I doubt the effectiveness of this method, but the author assures of its absolute efficiency. The idea is this: plants need to be covered “head to toe” with hay or straw, and not in a dense layer, but loosely. For specimens growing near walls and doors, the covering layer can be a little thicker. That’s all, actually. If anyone has tried to protect seedlings this way, tell me what happened in the end – it’s very interesting.
Such shelter will clearly not be enough.
Hot water
There are several options for use, depending on the degree of temperature drop. If the temperature drops slightly, it is enough to put several buckets of boiling water in the greenhouse in the evening. If the forecast promises a serious minus, you can additionally pour hot water on the path between the beds. Some advise additionally sprinkling the wet soil with dry soil so that the earth cools more slowly. Despite all the simplicity, the method is reliable, tested in practice, so use it with confidence!
Water in containers
Perhaps, this method in my personal rating claims the first place. Several tanks (canisters, bottles) with water are placed in the greenhouse. During the day, the sun heats the water, and at night the containers work as heating batteries. According to a reader who has been protecting her plants this way for several years, the bottles of water stand in her greenhouse for years, so there is no need to worry about sudden return frosts – they will not take you by surprise.
Fire will help us
The most common way to protect against the cold is fire. I would like to use it to my advantage, but how? It is dangerous to make a fire: strong fire can harm plants, and if the greenhouse is film or polycarbonate, then it will not take long to lose it. But should summer residents get used to overcoming difficulties? A solution was found, and not just one!
Candles
Even such a small fire source can resist freezing. For safety reasons, the candle must be placed in a container made of non-flammable material (a saucepan, a metal bucket, a ceramic pot).
If the candle burns too quickly, replace it with a kerosene lamp.
Additionally, you can place a heat accumulator on the container – a brick, a cobblestone, a miraculously preserved cast-iron grate, etc. In the evening, light a candle and calmly go to bed; by morning it will go out, but the heat accumulators will not have time to cool down. A small nuance: try to install the candle strictly vertically, then it will burn for as long as possible.
If the topic is relevant to you, be sure to read the comments to this question: in them, readers share their practical experience of heating greenhouses in this way. By the way, take note: a worthy alternative to quickly burning candles is homemade oil lamps or good old kerosene lamps.
Brazier
The method seemed labor-intensive to me, but I must give credit to the author of the idea – he tried to foresee all the important nuances.
Don’t skimp on firewood to make more coals!
The essence of the method: a large fire is made in the open air in a barbecue to make a lot of coals. As soon as the flames die down, they are sprinkled with sand or ash – this way they will smolder longer. The red-hot brazier is carefully transferred to the greenhouse and placed approximately in the middle; on the sides (from the side of the beds) and on top they are covered with sheets of slate or asbestos. Then a high greenhouse made of film is placed over the beds and the barbecue. According to the author, these measures are more than enough to protect seedlings in a polycarbonate greenhouse even at -15 ° C outside.
Heaters
I will mention them briefly, since this method of temporary heating of greenhouses is probably known to everyone.
A household heater can be moved to a greenhouse during periods of frost
A friend saved seedlings in a small film greenhouse with a small household fan heater; many summer residents speak approvingly of infrared heaters. Since we are not talking about a permanent type of heating, you can temporarily move an electric fireplace and a wall convector into the greenhouse, as long as the precious seedlings survive!
With the result that
To conclude the review of methods, I would like to warn readers against possible mistakes. Remember that there is no universal method that suits absolutely everyone! What worked in a film greenhouse may not be effective in a glass one. Volume, tightness and even air humidity are all important, everything needs to be taken into account. The only safe way I see is to first test the method in specific conditions, and only then plant the seedlings.
Browse other materials on the topic that may be useful, and be sure to check out the comments – in them, summer residents share their experience of protecting greenhouse plants from the cold: