Cacti often suffer by unhealthy influence of growing conditions. Most cacti and succulents are expected to flower when they reach the mature size, or even before, and failure to flower may indicate unsatisfactory growing conditions. The most important causes of physiological disorder are:
- Low temperatures
- High temperatures and direct sunlight exposing (sun scorch and heat damage)
- Over-watering and under-watering
- High air humidity
- Inadequate substrate PH value
- Harmful chemicals
Very low temperatures make cacti grow slower. The root stops its activities and it can ret if substrat is not dry. Although many cacti and succulents are surprisingly cold-hardy if kept absolutely dry during the winter, some species from perpetually tropical climates can suffer damage to the soft tissues at their growing points, and scarring and collapse of their stems leading to fungal attack and death of the tissues.
During the vegetation period our plants should not suffer by low temperatures. If temperature drops below water freezing point they can die. Dead cacti are hard and their epidermis loses its gloss. If we replace them to wormer room, stem becomes soft and starts rotting rapidly. It is very important to know lowest temperatures for each plant we grow so we can save it timely. Spring frosts are especially dangerous for tropical plants, not as much as those that come in autumn.
After all, if you think your plant starved with cold than put it away from light and warm it slowly - let it unfreeze gradually.
Scorch can affect plants if there is a sudden period of sunshine after the dark winter days, or even after a prolonged cloudy period during the summer. Sunken brown or white patches develop down one side of a plant where the tissues have effectively been "cooked" and the green chlorophyll destroyed. Sometimes a plant loses all its green pigment through excessive heat alone, even though it may not have been in the direct sunlight.
Scorching can be avoided by the timely application of shading to the greenhouse, improved ventilation and air circulation within the growing area to even out air temperatures. When moving plants into direct sunlight, or putting them outside for the summer, harden them off gradually in diffuse sunlight or put them under mesh shading for a few days to acclimatise.
Seedlings are very sensitive to high temperatures. The most important here is preventive. We can protect young plants by keeping them away from direct sunlight and periodically airing the room.
High air humidity, substrate over and under-watering
Over-watering is probably the single most common cause of failure of succulent plants to thrive. The plant may appear to do well at first, its leaves plump up and new growth produced. However, the roots may be suffering in wet soil and begin to rot unseen. The plant still looks well as the few remaining roots are able to take up sufficient of the plentiful water. As the roots continue to die in the stagnant soil, a point is reached at which they are unable to supply sufficient water and the plant appears to be suffering from lack of water. If more water is supplied, the situation gets worse and the rot may spread upwards into the basal stems or plant body. Eventually the plant body is observed to be soft and discoloured, perhaps yellow or grayish, by which time it is usually too late to save it. The moral is, that if a plant appears to be failing to take up water, knock it out of its pot and examine the condition of the roots before supplying more water.
If unsufficient water is provided for the prevailing temperature and stage in the growth cycle, leafy succulents stop growing and may shed their leaves and the apical tip of stems may die. This is followed by die-back or self-pruning of stems and branches. Cacti may shrink back into the potting mixture and possibly take on a reddish or purple hue because of production of coloured stress pigments. In some cases, shrinkage of a cactus during drought produces irreversible folds in the plant body which never fill out again. However, careful watering usually reverses the effects of drought on succulent plants. Small amounts of water should be given to water-starved plants at first, in case some of the roots have been lost.
Cacti become more sensitive when disposed to high air humidity for long time. That may happen in jars or green houses and than they can easyly fall sick (fungi attack) or start rot. Dry air can also affect plants in several ways: it can slow growth or red spider mites can spread over. If we have damp air - ventilating is recommended, opposite, if air is too dry - we should dew plant as well as water all other plants that surround it.
Plants kept with insufficient light grow with pale or yellow sometimes stunted leaves and elongated relatively thin stems with long spaces between the leaf joints. This is known as etiolation. Cacti become soft and elongated with weak spination. The condition can generally be reversed by providing stronger light, although elongated growth in cacti will always remain as a record of the change in growing conditions. Succulent plants can often be pruned to restore their shape.
PH value and nutritional salts
Cacti plants can hardly survive when placed in too accidic or too alkaline soil.If the PH value is lower than 4 or higher than 7, these plants start suffering from growth disorders similar to those caused by humidity deficiency. Therefore, you should always use soil mix and fertilizers with PH values between 5.5 and 6.5. If you see the plant is not responding well to present conditions or doesn't 'feel well' in the soil it is planted in - you should repot it as soon as possible. Before watering your plants, let the water sit overnight, or even better for 24 hours, so that the chlorine can evaporate off.
Lack of some nutritional elements (N, P, K) or microelements can also cause plant deformations. By learning the simpthoms of each element deficiency we can recognise the problem easily though, whenever you notice growth stagnation - first thing you should do is to repot the plant.
Harmful (dangerous) chemicals
There are plenty dangerous chemicals: gases, common pollutants such as Formaldehyde (used in many building materials including particle board and foam insulations, cleaning products...), Benzene (common solvent found in oils and paints), Trichloroethylene (used in paints, inks, varnishes) etc.. You must, of course, always be very careful when using fungicide/insecticide solutions so that they wouldn't harm your plants. Injuries caused by these chemicals usually look like dark spots or hardened (wood-like) parts of the plant. Unfortunately, when you see these symptoms it is usually too late to do anything. What you can do if such thing happens is to remove what is causing the injuries and expose the plant to as much fresh air as possible. To prevent mistakes from happening, all the products should be used and applied following label instructions on the product.
Special thanks to Maja Jokanović