Heating and ventilation of the nursery

 No matter how you set up your nursery, it is important to heat and ventilate it adequately. This is a basic principle to produce the most beautiful transplants possible.

One of the most common mistakes is trying to save money by adjusting the thermostat. of the greenhouse to a lower degree than necessary to optimal plant growth (18 ° C at night). Since heating a greenhouse on a frost night costs expensive, it's an understandable reflex but, at the end of the account, we lose. Indeed, the plants will grow more slowly and production will be delayed. In an already very short season, we must grow the transplants as quickly as possible. To reduce your heating costs, you should rather look on the equipment side (better insulate the greenhouse, provide a more efficient furnace, install a heat shield, etc.) and, above all, always make sure that the greenhouse is hermetically sealed at night and completely sealed against cold winds blowing at outside.

When it comes to heating, there are oil, propane, or gas systems and they are pretty much all equivalent in terms of cost. In my opinion, none of them is more ecological than the others.

You can also heat with wood, but I do not recommend this system. Get up several times per night to power the heating system is a painful task and it is not easy to maintain these systems at a predefined temperature. Through cons, it is imperative to equip yourself with a furnace recent and in very good condition, because it will be more efficient and more reliable. It will also be necessary that the furnace is sized to heat the space required: a small furnace that does not animate to supply will burn more fuel than a large which will heat quickly to the desired temperature.

The reliability and speed of the services offered by fuel suppliers must be taken into account when choosing a type of furnace. Some of them offer agricultural tariffs advantageous and it is good to inquire about it. In addition, to avoid running out of fuel, always make sure that your tank is sufficiently full during a frosty night or cold.

To distribute the heat evenly, we use perforated polythene tubes (which are called balloons) which are connected to the furnace and installed under the tables, to heat before all seedling trays. The perforations in these balloons must be calibrated according to their size and their spacing within the tight. Most of the equipment suppliers of greenhouse offer this service.

To cool the nursery during the days sunny, there are different solutions. We have chosen natural ventilation through the opening sides (roll-up, in English). While several Fan-Jet-type fans do a more precise job, we like the "passive" aspect of this system that allows hot air to be expelled by the simple action of the wind which enters the greenhouse.

To prevent wind and cold air from entering too direct contact with transplants, we have installed "skirts" along our tighten and place our sowing tables lower than the side openings. This kind of installation is very common and greenhouse manufacturers can provide details and recommendations in this regard.

In terms of humidity control, we got into the habit of opening side openings for a few minutes, very early in the morning, to let out the humidity produced by the condensation of the night. I also recommend doing it while the furnace is on. Adopt this good practice allows us to prevent excessive humidity from remaining stagnant and, to this day, our nursery did not suffer from any significant fungal disease.

Finally, one of the essential instruments of the nursery is a thermometer with an alarm to set minimum and maximum temperature limits. In the event of a furnace failure, lack of electricity, or fuel, this alarm will warn us of the danger lurking in our production. This is particularly important on freezing nights, while a few hours without heating can be fatal to seedlings. Such a scenario has happened to us more than once, but luckily we had planned a breakdown plan. If it is a furnace failure, our greenhouse is equipped with an auxiliary furnace that we maintain regularly. This second furnace is much less powerful than the main one (and cheaper!), but it minimally heats the greenhouse while waiting for the services of a repairman. After several seasons of denial, we are resigned to getting a generator emergency, in the event of a power failure. This last represents a significant investment and will probably never be useful, but we have to admit that we would have a lot to lose if the power ran out for several days. Sometimes you have to put on the suspenders and the belt, as my grandfather said ...

In the same vein, the alarm of our thermometer is also essential for warn us of an overheating of the greenhouse during the day. Forget opening the side openings when the sun appears can quickly destroy seedlings. It can happen in less than two hours! Such a mishap would affect seriously the whole season. Therefore, there is no room for error. A thermometer equipped with an alarm is quite simply essential in a nursery.


Good irrigation management is essential in the success of seedlings. A lack of water can quickly cause the death of seedlings, as too wet soil creates conditions conducive to fungal diseases. Determine when to water and how much water is not so easy and many parameters need to be taken into account :

~ Watering should be uniform. Trays of the same size should all receive the same amount of water so that none of them dries up faster than the others. Pots and trays with cells larger will require more water. He imports therefore to arrange them in such a way that they are grouped by size on the tables (the 72 trays in one place and the trays of 128 to another).

~ It is necessary to water according to the state of the trays in the greenhouse (drying is generally faster on the edges of tables, the south side of the greenhouse, and near the furnace, for example).

~ The watering must be done in two stages: a first to wet by capillary action and a second to wet the cells deeply.

~ Finally, we must take into consideration the outside temperature at the time of waterings. In sunny weather, you need to water in-depth while in cloudy weather, watering should be lighter, even avoided. 

A devastating disease like "Damping-off" is often caused by potting soil that cannot dry out. Foliage plants that stay wet too long are also a gateway for various fungal diseases.

Managing all these parameters well requires a sensitivity that develops through careful observation. and continues the soil of the plateaus and the appearance of seedlings. This is the reason why, in our nursery, there is only one person who occupies watering. It is also the best way that we have found to ensure that this important task is never forgotten. The person manager may delegate it on occasion, but the responsibility always rests with him. It's a way to do that I highly recommend.

It is also important to avoid watering the sowing with water that is too cold, which impairs the growth of the plants. To solve this problem, we have a large capacity water tank (a 1000 liters does the trick) which tempers the irrigation water. The heat of the greenhouse heats the water which, otherwise, would come directly from the well. To increase this effect, we painted the tank in black. In doing so, we also limit the proliferation of algae in the tank. This last one is connected to a swimming pool pump equipped with an expansion tank. In this way, we can water at will without having to switch off or on the pump constantly.