Proper irrigation system for greenhouse crops for a stable harvest

It is funny, but every grower is confident that they know how to irrigate. Why is it funny? Because, in my observations, this is a very rare skill, and the highest yields are obtained by those rare growers who actually know how to irrigate.

Usually, people under-irrigate their crops or become victims of their unexpected overwatering during rains. So, what does it mean to feel the golden mean in irrigation, and what does it actually "look" like in liters?

Crops do not get enough rainwater; every grower should clearly understand this, regardless of the cultivation method — whether in open ground or in a greenhouse. Accidental yields are the result of this misunderstanding. There was plenty of snow in winter, and one was lucky with rain in summer — only then is there a harvest, in certain years... In such rainy seasons, "water savers" are encouraged: "See, it works! This is how it should always be!" In dry years, they lament: "Oh, again, no luck with the rain!"

But how could it be otherwise: the scientific precipitation statistics are well-known, where the amount of rain cannot often exceed the average values of 600–700 mm. Try as you might, these limits are the boundary! Crops clearly do not get enough from 600–700 mm, so high yields will only occur in those rare years when precipitation is above the average value, say, 1000 mm per year, especially if the "extra" comes during the summer. This is that rare and productive rainy summer, but it is by no means appropriate for us to take it as the norm.

If you want to have constant yields every year, you will have to develop an irrigation system. This does not mean choosing an economical automated drip irrigation system, but learning to give your plants the required doses of water. Specific daily doses for each crop will be indicated below, and now we need to establish a theoretical basis for them.

It was not common practice in the past, and now, after the introduction of water fees, it is even less so, for people to irrigate apple trees, fruit bushes, potatoes, etc. For greenhouses, this restriction not only applies but is reinforced under the pretexts of:

• combating late blight;
• suppressing the growth of foliage;
• other reasons.

Water is a vital factor for plant life along with heat, light, and nutrients (there is no strict hierarchy, they are all equally important). Consequently, growers "burn out" due to fluctuations in soil moisture and excessive jumps in both directions — from overwatering to drought — just as often as they do due to excessive fertilizer and temperature.

This is the motto of a competent greenhouse manager who knows the characteristics of their crops and their changing water needs. What kind of irrigation should we organize separately for each crop? Irrigation of tomatoes — tomato, perhaps, is one of the greatest water consumers.

Judge by the scientific irrigation standards:

This standard, of course, is not for seedlings or a young blooming June bush, but when the bush in the greenhouse is in the flowering period, tall to the ceiling and covered with growing fruit sets. It currently has a very large total biomass and a large leaf surface area, and they evaporate a lot of water. During this time, the bush needs water for the growth of shoots and the fruit sets themselves, as well as for general life maintenance (photosynthesis and everything else).

Any plant lives by pumping water through itself, evaporating it through the leaves. Only about 5–10% of the irrigation water remains in the plant; the rest must evaporate, and the grower should not try to "correct" this difference, as it is no longer within their control. They must irrigate!

How much water does a greenhouse with tomatoes require after a sunny day? So estimate and multiply how many bushes you have there, and each one on a hot day needs about 3–4 L of water for free development, or at least 2 L. That is approximately a bucket (watering can) of water for three plants. On cloudy days, you can irrigate every other day — 1 L per plant.

If you do not give them enough water, they certainly will not perish; they will extract it from the depths of the soil (but they certainly won't find 3 L per day for each one there) or from the morning dew; finally, they will draw water from the stems and leaves into the fruit. Of course, at the same time, shoot growth will almost stop, and the fruits will be small.

With a lack of water, plant development stops prematurely, and the harvest is reduced.

Sometimes this is to the owner's advantage: in a short summer, it is more beneficial to accelerate the ripening of fruits, however, we all use the capabilities of a polycarbonate greenhouse because it powerfully expands the boundaries of summer, so even southern cultivars sometimes ripen in it.

Irrigation of eggplants

Unlike greenhouse tomatoes, the eggplant bush is noticeably smaller in size. It has a height of no more than waist-high, while it is less branched, and does not grow the same number of active side shoots. In addition, there are fewer developing fruit sets on an eggplant bush, usually only 3–5. The fact is that when overripe, eggplant fruits become coarse and lose their taste, so they are usually harvested at a young age.

And this is even beneficial for the remaining fruit sets: the sooner the largest one is removed, the more actively the others grow.

They are suitable for frying even when they are very young and shortened, before reaching full size. This crop is very convenient: you can regularly walk around the planting and harvest the largest fruit set from each bush.

So it turns out that the water consumption of an eggplant bush is not that great, and 0.5–1 liter of water on a sunny day for an adult plant will be enough. True, it is planted more densely than tomatoes, so water consumption for irrigation, calculated per square meter where 4–6 plants grow, can be comparable to an ordinary open-ground garden: for example, a bucket of water per square meter every 3 days. If you give more, it certainly won't hurt.

Irrigation of sweet (bell) pepper

This plant in many ways resembles an eggplant in its water requirements. It is also low-growing and compact. The largest fruit sets are also regularly removed from it, sometimes without waiting for their full ripening and reddening.

Irrigation rates for sweet pepper can be taken the same as for eggplant — 0.5–1 liter on a sunny day per adult bush. Consider that with 1 liter, the increase in total biomass will increase by 50 g per day (a quarter of a cup) instead of 25 g with 0.5 liters. Not all of this biomass will go into the fruits, but still, they will grow quite well.

Usually, by the end of summer, all eggplants and peppers undergo fruit set normalization; all upper and unpromising "second-tier" fruit sets are removed, not to mention flowers, so that water is not wasted in vain. Only those medium-sized fruit sets that have the opportunity to slowly grow to a consumer state in the conditions of a cold autumn are left. In a warm autumn, the fruits of eggplants and peppers can hang in the greenhouse unharmed until November, gaining weight. It is clear that at this time they are watered much less: wet cold soil bodes nothing good for them, and there is no benefit from watering when the growth of fruit sets has almost stopped.

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Note. I am not writing about hot, or chili, pepper here, although if desired, it is grown in a greenhouse in exactly the same way as sweet pepper. The fact is that this crop is so simple to grow that its fruits in the Central region can be obtained even in open ground, through transplants, of course. Precious space in the greenhouse is not spent on it.

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Irrigation of melons

An adult melon vine consumes about 2–3 times less water than a tomato bush, and about 2–3 times more than a watermelon.

Melons in a greenhouse are often watered in the following mode: every 3 days, about 3 liters of warm water per plant, depending on its age. It is clear that small bushes do not need that much water. Most of the water is consumed by a multi-meter vine that has spread in all directions with fruit sets that have begun to grow.

With less frequent watering, when the soil dries out for a long time between intervals, the melon can be infested by spider mites. The appearance of this pest often occurs with dense planting and without pinching the side shoots, when the surface area of the leaves of each plant becomes truly huge. In such conditions, the leaves lack both light and water, and the resistance of the plants weakens. Pests and diseases always react sensitively to the weakening of the "will to live" of the foliage.

Conclusion

The irrigation water rates for a single plant indicated anywhere in reference books are conditional, since the needs of the bush can change several times depending on its training. For a melon vine that has freely spread in all directions, 1 liter of water on a sunny day is a pittance. At this time, its water consumption is comparable to a cucumber — a famous water-lover. It is customary to pinch the side shoots of melon vines in greenhouse conditions in order to wisely reduce the number of leaves and, accordingly, water consumption. If you do not train your plants, and have also listened to advice to "not water the melon field at all," then consider that you are guaranteed to have spider mites. A melon grower has to gain the skill, or intuition, through experience to determine the needs of the bush depending on its size.

By the way, melons are not watered directly at the root; one should try not to wet the root neck during irrigation, as it may suddenly rot. Sometimes you get away with it, anything can happen…

Watering watermelons

The watermelon is characterized by the lowest water consumption, but this does not mean that it never needs watering. While in the open field in the Central region, watermelons are often not watered at all under many cultivation methods, it is too hot under a transparent dome, and water requirements are higher. As the vines grow, watermelon bushes are watered, albeit modestly, and during the most vigorous growth period of the bush, even before fruit set, they are watered like melons — 2–3 liters per plant every 3 days.

By the time of fruit set, the plant must have already developed a sufficiently extensive leaf apparatus capable of confidently nourishing the fruit set. After that, you can stop watering: the root has become large and will provide for the bush.

It is believed that as soon as 1–2 fruits appear, about the size of a walnut, watering should be stopped.

• Pinch all side shoots so the plant no longer wastes water on their growth.
• The fruit set should then grow "slowly but surely," at the expense of dew and the extraction of moisture by the roots from the depths.

A feature of the watermelon as a cucurbitaceous crop is its very high root suction force. Its root is capable of drawing water from almost completely dry soil. Thus, the watermelon's root network extracts soil moisture both from below (though unlike in Central Asia, our deep soil can be too cold) and from the surface: at night, upper soil clods become saturated with moisture via capillaries from dew, and the watermelon successfully absorbs this water, as well as the dew on the leaves. This is how this plant adapted to growing fruits in an arid climate.

Attention. When the watermelon fruits have become large, weighing about a kilogram, they often crack from sudden, abundant watering. Such cracked watermelons do not ripen; they rot, and they can be cut and discarded immediately. This is also one of the reasons why watermelons are not watered at all in the second half of summer.

Many vegetable growers rely on natural precipitation that flows down the slopes of the greenhouse and saturates the soil at the edge beds. Indeed, if it rains at least once every two weeks, tomatoes will continue to grow, but the fruits will significantly underperform in weight. Basic irrigation rates are calculated exclusively for dry weather, when there is no rain at all.

Care mistakes: leaf removal and evaporation control

In the practice of growing tomatoes, there is a mistaken belief that complete removal of leaves increases yield. If you strip the foliage as early as June, the fruits will indeed turn red earlier, but they will remain small and underdeveloped. Without a leaf apparatus, the filling of the fruit set proceeds only through weak photosynthesis of the stems, which leads to a loss in the total harvest mass.

Often, such methods are resorted to out of helplessness against late blight, which is capable of completely destroying the crop. Because of this disease, other specific technologies arise, such as growing tomatoes in bags. Only those techniques that have been verified by many years of practice and guarantee protection against late blight can be considered effective.