Heat, as well as light, moisture, air, nutrients, is one of the basic conditions of plant life. All living plant cells are separated from the environment by cell membranes.
Membranes consist of lipid and protein molecules, and it is the lipid composition of membranes that changes significantly depending on illumination, temperature and acidity. In particular, under the influence of high temperature in membranes, the amount of unsaturated phospholipids increases, which increases the permeability of membranes, increases the viscosity of the cytoplasm, amino acids (proline) capable of osmoprotection begin to be produced (prevent dehydration by holding water and maintain electrolytic balance), organic acids that bind ammonia.
These adaptive changes in metabolism are genetically determined, and are expressed in different plant families to varying degrees. More precisely, due to the ability of plants to adapt to high temperatures, they are classified as:
- non-heat-resistant plants - are damaged already at + 30-40 ° С (aquatic flowering, most mesophytes and hygrophytes).
- frying plants - which tolerate short-term (about half an hour) heating to + 50-60 ° С (plants of dry habitats with strong insolation - steppes, deserts, savannahs, dry subtropics ).
Mesophytes (the first group) include most indoor plants that live in nature under conditions of sufficient, but not excessive, moisture. Mesophytes are examples: dracenes, citrus fruits, ficuses, palm trees, roses, petunias, etc. Hygrophyte plants are moisture-loving plants in room culture: phyttonias, begonias, philodendrons, etc. These non-heat-resistant plants are the first to wilt at high temperatures.
So, when the temperature of the surrounding air rises, in order not to overheat, the plants reduce their temperature by transpiration (evaporation of water by leaves). If the temperature continues to rise, the intensity of respiration begins to prevail over the processes of photosynthesis, the formation and accumulation of organic substances in the plant ceases, and water deficiency occurs. Subsequently, damage to cell membranes and denaturation of proteins occurs. The plant first wilts, stops growing, then dies. And if some higher plants can tolerate short-term heating up to + 50-60 ° C, then active photosynthesis, even in desert plants, is inhibited at temperatures exceeding + 40 ° C.
The temperature limits in which photosynthesis processes can be carried out are different for different plants. In addition, temperature affects photosynthesis depending on illumination. So, in low light, photosynthesis does not depend on temperature in any way, i.e. in low light, photosynthesis proceeds at the same rate both in heat (+ 18-20 ° C) and in cool (+ 8-12 ° C). In good light, a decrease in temperature inhibits the process of photosynthesis, reducing the activity of enzymes involved in dark reactions. In most indoor plants, the intensity of photosynthesis reaches a maximum in the temperature range of 20-25 ° C, with a further increase in temperature, it decreases, and at a temperature of 40 ° C, photosynthesis almost completely stops. Therefore, the maximum limit of optimal temperatures for plant growth indicates 28 ° C on our graph.
Why do you need to know all this? This is important, first of all, for those who bring their plants to the glazed balcony or loggia for the summer. The fact is that in summer the temperature in the shade on hot days rises to + 26-28 ° С (in central Russia). If the balcony faces the shadow side, with the windows closed, the temperature there can reach + 35 ° С. And if the balcony is on the sunny side - everything is + 50 ° С. I.e. if you accidentally forget to open the windows, your plants will at least slow down in growth, and will be very dehydrated, at worst, they will simply burn and die.
According to the degree of adaptation of plants to conditions of low temperatures, the following classification exists:
- non-malt-resistant plants are most plants in rainforest, they are not able to tolerate a decrease in temperature to + 5-8 ° C. I.e. plant cells are damaged before the temperature drops to the freezing point of water. In the encyclopedia of indoor plants for such plants, a temperature minimum of 12 ° C is indicated.
- non-frost resistant plants are plants that tolerate a strong decrease in positive temperatures, but the limit lies at a point just above 0 ° C. Such plants include the so-called greenhouse plants, for example, acacia, cypress, laurel, citrus fruits, etc.; as well as some cacti and leaf succulents .
- frost-resistant plants - plants that remain viable even at subzero temperatures, because crystalline ice does not form in their cells even during freezing (many plants of moderate latitudes). I must say that in potted culture, even initially frost-resistant plants, for example, birch, planted in a pot like potensai (for the formation of bonsai), risk freezing in winter. Therefore, even frost-resistant plants, when grown as indoor and greenhouse plants, are kept in winter at temperatures ranging from + 1-5 ° C, and only a short-term decrease to -3-4 ° C is allowed.
Heat for plants
Simplifying all classifications, for an ordinary florist, we divide (conditionally) all plants according to the temperature regime into: indoor plants of warm and cool plants. In warm rooms, the temperature ranges from 16-20 ° C in winter (normal room temperature in summer), in cool rooms - an average of 12-14 ° C (the lower limit depends on a specific species, for example, for myrtle, some palm trees may be 6-8 ° C). In warmer rooms contain plants of tropical countries. Plants of subtropical countries and hardy plants of tropical countries grow well and develop in cooler rooms .
There are plants that are not demanding on the temperature of the room (aloe, aspidistra, dracena, monstera, ficus), i.e. they can grow well both in warm and cool rooms, if you observe the balance of light and watering. I.e. lighting is always equally good, and watering decreases when the temperature drops, moreover, the colder the drier, up to the complete drying of the ground in the pot. This is because the absorption of water by the roots of plants is difficult at low temperatures (as well as with high soil dryness, salinity or strong acidity). And if the plant is watered beyond what it can absorb, suck up and use up, the roots simply rot.
Some plants are very sensitive to very sharp daily temperature differences when the difference is 10-15 ° C. But this is only if the plant is in moist ground. It should be remembered that in winter the temperature near the window is 1-2 ° C lower than in the room, and on the windowsill, lower by 3-4 ° C (the difference can reach 5-8 ° C). In addition, the ground in the pot (around the roots) is also lower than the ambient temperature by about 1-2 ° C. If the plant stands on a windowsill on which 16 ° C, then in the roots after watering the temperature can be only 13 ° C. And this is already on the verge, for some plants. Therefore, in order not to guess on the coffee grounds, focus on the thermometer located on the windowsill. However, if the roots of the plant are in only slightly moistened soil (i.e. moisture is not even felt by the hands, it is somewhere in the very depths of the pot, the earth is not damp) or practically in dry land, then even significant temperature fluctuations are not afraid of it. Even a small draft is not scary if it does not cause cooling of the ground in the pot.
Effect of temperature on plants
There are plants that need diurnal temperature fluctuations when daytime temperatures are significantly higher than nighttime temperatures. These are many orchids, succulents, cacti, in their historical homeland these fluctuations reach a corridor of 20-40 ° C! And if you do not provide them with these changes, the plants will not bloom. But that's not all. Many plants, in addition to daily temperature fluctuations, need special light conditions to plant flower buds. For example, the well-known azalea and decembrist (schlumberger) for flowering need a decrease in temperature to 10-15 ° C in conditions of short daylight hours.
If specific temperatures are not indicated for the plant, but it is said like this: moderate, not lower than 12 ° C, this does not mean that the plant should grow at 13 ° C constantly. The fact is that the lower limit is indicated, which is possible for a short time, a day - two. But if the plant is constantly grown at its temperature limit, then it will hurt (unless the plant is at rest). The temperature for good growth and development should be optimal. I.e. for plants in need of moderate temperature - 15-18 ° C, heat-loving - 18-24 ° C. It should be emphasized about the detrimental effect of too high temperatures in combination with dry air and lack of light. The high temperature encourages the plant to grow, and the lack of light affects the processes of photosynthesis. As a result, the shoots stretch, the internodes increase, and the leaves pale and grind. A vivid example of such a detrimental effect can be seen on indoor roses, they need a temperature of about 10 ° C in winter.
