General information about cacti
In general, there are different growth factors that are responsible for the welfare of our cacti. On this page I would write something more about these basic conditions which are very important.
Sunlight is very important for all plants becaus it allows photosynthesis and therefore growth. Depending on the quantity and quality of light the growth of plants is affected.
Cacti need a lot of light because they comes from areas where they get a lot and very bright light.
To this a short comparison:
The light values in the winter In Central Europe are sometimes under 3000 lux, whereas the light values reach 60,000 to 100,000 lux during sunshine in the summer in the habitat of cacti.
The most important components in the light for cacti are the ultraviolet (UV) - and infrared (IR) radiation.
UV radiation which is cold light in the range of 250-400 nm, hinders growth of length.
The plants that are exposed to excessive UV radiation, such as cacti from high altitudes, look more compact and have stronger spines.
IR radiation which is warm light in the range above 750 nm wavelength supports growth of length.
Cacti which get more of IR radiationthan UV radiation grow unnaturally stretched.
So that cacti get as much UV radiation as possible they should always exposed to direct sunlight. This is extremely important especially in Europe and the northern countriesbecause the air and the glass of a greenhouse filteres much more of UV radiation then of the IR radiation.
After a familiarization phase, especially in spring when the cacti come from their dark winter quarters they get slowly used to the bright sunlight by shading. This is especially important in late summer and fall. This supports the formation of fine and dense spines and servs to harden the plants.
Temperature is an important element for the development of plants. Cacti grow in areas with very high temperature differences. The temperatures on sunny days in summer can be up to 40°C (104°F) and drop down over night to 5°C (41°F) and below. In winter temperatures are generally lower. So on sunny days temperatures can reach from 10 to 25°C (50 to 77°F) and from 0 to 5°C (32 to 41°F) during the night.
So the plants are depending on the soil temperature on the one hand and on the air temperature on the other hand.
Cacti which grow in warm regions won't show a pleasable growth when they have a too cold soil temperature because the intake of nutritions is affected by that. The best soil temperature during the growing season should be 15 to 30°C (59 to 86°F).
Because most cacti in our collections grow in pots or bowls the substrate can be heated on a sunny day up to 50°C (122°F) or cool down in very cold nights.
To decrease this a little you can shade the plants during the day. Or you pot the pots in a mix of quarz sand or a mix of sand and peat.
To achive a healthy growth in summer air temperatures between 20 to 25°C (68 to 77°F) during the day and 12 to 22°C (53.6 to 71.6°F) during the night would be best. However, the temperature can rise up to 35°C (95°F). At higher temperatures the plants stop the growth.
In order to avoid high temperatures, especially in small spaces such as cultural hotbeds or greenhouses it is necessary to air a lot in summer. Furthermore you should shade to avoid a fast overheating.
In greenhouses the paths can also be moistened with water to create evaporative cooling.
The air consists of oxygen and carbon dioxide. The absorption and release of these gases occurs through the stomata in the upper cell layers of the cacti. To ensure this, the plants always need fresh air and sufficient air movement. If the plants stand in stagnating and stale air for example in a poorly ventilated hotbed or greenhouse, the exchange of gases is hindert. The plants will begin to look bad under these conditions and they will be also more delicate to diseases.
In the absence of ventilation and air movement and concurrent solar radiation, like in a greenhouse the plants will suffer some serious sun burns and die after a long time the "Death of heat". Good ventilation is also an important factor to harden our cacti and thus make them more resistant against diseases and pests. Especially fresh weaned and effeminated plants attract most to pests.
You have to mind that the plants don't get placed in a draft. The damage due to drafts would be one-sided desiccation in summer and in worst case damage due to frost in winter.
Without water, there is no life. Cacti occur on dry sites. Due to their adaptability, they have become accustomed to ground and air dry. But without water, even cacti can not live.
The water demand of cacti varies with the seasons and the size of the plants. Especially during the flowering and growing season mainly in spring and summer, the need of water is greater than in the resting season.
Cacti which are exposed to high heat need more water than those in cooler places. This happens due to the higher evaporation under heat. You also have to consider humidity. More moisture is released in dry air. When watering the size and the type of pots also matters. Moisture holds much longer in plastic pots than in the clay pots. The temperature of the substrate is also important. You should never water pots which are heated from sunlight! The result would be scalding the roots.
In spring and fall you should water in the morning and in summer only water in the evening. The frequency of watering always depends on the size of the plant and its pot.
Large plants and pots = large water requirements and vice versa.
Between watering the substrate should dry out every now and then. Even a forgotten plant won't dry out so soon.
You shouldn't water your plants during cold weather. Cacti which stand in moist soil during cold weather can easily rot.
Which water should I take?
Tap water in many places is very hard by the dissolved limestone which may mean that the substrate in our pots can be quickly alkaline. You can easily recognize this by the lime verges on the pots. The consequence is that the plants stop their growth. The only solution would be an repotting.
Furthermore chlorine is added in tap water to kill germs and bacteria. So you shouldn't water your seedlings with tap water.
Rainwater is soft, but may contain dirt. Depending on the air pollution in the corresponding region, especially when its close to industrial constructions, the collected rainwater could also contain sulfuric acid. This combines with the zinc from the gutter and forms harmful zinc sulfide.
If you can bar this, then rainwater would be the first choice for cacti.
Nutrients are dissolved salts which are present in the water and in the substrate. Cacti need them to build and maintain their body. The main nutrients cacti require are nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca). Those are absorbed through the roots from the substrate. When these nutrients are used up or washed out from the substrate, they can be fed back through fertilization.
On the one hand you can use an organic fertilizer to fertilize the plants. This is for example cow dung, horn shavings, or guano. These substances are added to the substrate so they can give their nutrients slowly to the plants. Because of that they were also called „slow-release fertilizers“.
A good usage example is the mixing of cow dung into the substrate of leaf cacti because these plants have high nutrient requirements.
On the other hand there are inorganic fertilizer. These are water-soluble salts which are available in concentrated form known as compound fertilizer.
For these it is important to ensure fertilizers that they have a low nitrogen content. Since nitrogen is responsible for the vegetative growth too much of it would give our cacti an unnatural appearance. Furthermore, the flower formation and the flower willingness would also be affected. But this is affected by the phosphorus. Fertilization with phosphorus entails a rich flower and fruit formation.
For healthy growth and a strengthened body cactus plants need potassium. Especially at the end of the growing season in late summer and autumn the plants need a higher potassium content. Potassium strengthens the new young shoots, lowers the cold sensitivity, increases the resistance aiaginst diseases and promotes the bud formtion in the following year.
Calcium appears primary as lime which is added during the manufacturing of substrates. Lime bounds plant-harmfully acids, promotes the live of micro-organisms and opens up nutrients. Calcium has also a positive effect on root growth. In highly acidic substrates, e.g. if peat is added calcium brings the pH back into the desired area. But you can also get some problems if too much lime is dissolved in the substrate. The pH changes over a value of 7 which is undesirable. This leads, as previously described in the section over water to coccolites on the plant and in the substrate.
Other important nutrients are called micronutrients or trace elements. These are magnesium (Mg), appoint manganese (Mn), iron (Fe), copper (Cu), boron (B) and sulfur (S) just to mention a few.
When you purchase a fertilizer you should always make sure that these trace elements are included whereas the containig amount should be very low. A correct ratio of the main nutrients nitrogen, phosphorus and potassium would be 1 : 3 : 5.
The best time to fertilize is the growth period from April / May until early / mid August. During this time the plants are fertilized about every 10 to 20 days. Hereto the fertilizer in added in the stated amount to the water. Normally it would be 1 gram of nutrient salts per liter of water. You only fertilize the substrate which is already moist and which stands not in direct sunlight because this may cause damage to the roots. It is adviseable that you chose the 1th, the 10th and the 20th of the month to fertilize your plants. This avoids any trouble with the dates.