How do you get succulents into great condition? A large day-night temperature difference is the key

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Text and images: Curator

1. The effect of temperature difference on succulents

For succulents native to South Africa, the most suitable growing temperature for most varieties is between 12-28 degrees, and this figure should also be the average high and low temperature of the growing season in their place of origin.

In the Jiangnan region represented by Hangzhou, where Old Ginger is based, because it sits in the zone where northern and southern air currents meet and battle, it is often the case that just as the cold air leaves, the subtropical high takes over. Across the whole year, the days that can stay at 12-28 degrees are only in May, June, October and November, about 4 months in total. In most other months it is either too cold or too hot, so that often you go straight from a cotton-padded jacket to short sleeves, and after wearing short sleeves for two days you suddenly need a sweater again. (This is also why spring and autumn clothing sells poorly in Hangzhou.)

The human body can barely endure this kind of climate, but for plants, especially succulents, it is quite troublesome. Some people say that a large temperature difference can promote plant growth. That is right, the day-night temperature difference really can promote plant growth. But you may not have understood the principle behind this growth. So let me explain it to you slowly...

How well a plant grows depends on how many nutrients it accumulates in its body. During the day, photosynthesis is a process of making nutrients. Within a reasonable upper temperature limit, the higher the temperature, the stronger the photosynthesis, and the more nutrients are made. We can regard this process as a plus for the plant's nutrient accumulation.

At night, because there is no light, the physiological process by which most plants make nutrients stops, and the plus is zero. But the plant's transpiration continues. So-called transpiration is the plant relying on the ambient temperature to make its leaves evaporate the water in its body, and at the same time, through the siphon effect brought by evaporation, prompting the roots to absorb water. This process consumes nutrients from within the plant, and can also be regarded as a minus for the plant's nutrient accumulation. The higher the ambient temperature, the greater the transpiration, and the greater the minus. So how many nutrients a plant can accumulate over a day depends on how much it makes during the day and how much it consumes at night.

Through the explanation above, I believe everyone should have some understanding now. The higher the daytime temperature, the more nutrients the plant makes; the lower the nighttime temperature, the fewer nutrients the plant consumes. The effect of the day-night temperature difference is reflected here. Why are Xinjiang grapes so sweet they stick to your teeth? Why do Xinjiang tomatoes taste like persimmons? It is not because the young men are hardworking, but because of the climate of "wear a fur coat in the morning and gauze at noon."

Alright, now that we know this principle, I believe no one will argue with Old Ginger about the difference between the two concepts of day-based temperature differences caused by sudden warming and cooling, and day-night temperature differences.

In fact, sudden warming and cooling caused by climate not only do no good to plants, but also cause extremely serious harm. They not only disrupt the plant's normal physiological order, but also trigger various accidents. In terms of physiological order: for example, in spring, after the temperature has finally risen for a period, the plant begins to show signs of growth, and you have already happily started watering and fertilizing, busy as can be. Then suddenly the temperature drops, and the newly grown leaves immediately freeze in place, not to mention the consequences of the water you poured and the fertilizer you applied. Just this frozen leaf alone may later trigger in you the urge to behead the plant. You say you won't behead it. Fine, don't behead it. A few months later the frozen leaf starts growing, pointed on top and round on the bottom, the whole thing shaped like a gourd... And that is still the good case. If they were all this shape, you could at least pass it off to yourself as a new variety. The problem is that among a ring of good leaves there is just this one gourd leaf. So will you behead it or not? Then there are accidents. A sudden drop in temperature after high heat is actually fine; South African succulents are fine with short periods below zero. But a sudden rise in temperature after low temperature is troublesome. In the dead of winter, the temperature suddenly rises to 25 degrees, and the well-sealed greenhouse, the temperature suddenly shoots up to 50 degrees. Done for. By the time you get back at night, a whole greenhouse of steaming steamed pork with rice powder is waiting for you to lift the lid... Besides these, there are also pests and diseases, fungi, and so on, all related to sudden temperature changes.

I think the summary of this small section needs to be stated separately - the temperature difference can promote the growth of succulents and the accumulation of nutrients, but it must be a controlled day-night temperature difference. Temperature differences caused by sudden weather changes are harmful, not beneficial, to plants.

2. How to create and use temperature differences

A home growing environment by definition makes it very hard for us to achieve the perfect artificial temperature difference of a greenhouse. (A greenhouse relies on the sealing effect of polyester film to store heat in sunlight, enlarging the temperature difference by raising the daytime temperature.) But the home also has its advantages. As long as you are not living in a pavilion, at least it is warm in winter and cool in summer, and extreme temperatures will not occur. So how to create a temperature difference requires finding a way within this not very obvious temperature difference at home.

(1) How to create a temperature difference in winter

Although I said earlier that I still advocate letting nature take its course, tinkering as little as possible, and making the most of existing environmental facilities, for the harsh winter in the south, letting nature take its course is equivalent to accepting nearly half a year of dormancy for succulents, especially Haworthia plants. This is unfair to the many southern growers. (Why do northerners get heating... the south has no coal but it does have natural gas... no family is short of that little heating fee, right?) So the winter temperature difference mainly relies on keeping warm during the day.

For keeping warm, the first thing to consider is sealing. A grower in Shanghai used large storage boxes or built "pigeon cages" outside the windowsill and achieved no small success. I hold a positive attitude toward both of these methods. When I talked about water control earlier I did not advocate them, but when it comes to keeping warm in winter, I think these two methods are still feasible.

But both methods have their own flaws. A storage box is too small in volume, and for growers with a larger scale of cultivation it is truly a drop in the bucket. A pigeon cage works during the day, but at night when the cold wind blows outside the windowsill, the internal temperature immediately falls close to the air temperature. Judging by Hangzhou's coldest winter temperature of minus 5 degrees, within a week all the Haworthia leaves will turn white and foggy, and then start to rot after spring begins. Unless you install an air heating wire and a thermostat. These two things, anyone with an electrician's certificate would not dare to use. Why? Go take the electrician's certificate exam and you will know.

After all, if you can tinker less, tinker less. Wrapping and sealing an existing flower rack is a relatively eco-friendly approach. Common flower racks generally come in two types, wooden and metal. For a wooden flower rack, it is recommended to wrap and seal it directly with polycarbonate sheets. (It looks better and the insulation effect is also good.) Except for the front and the bottom, the other 4 sides can all be fixed with wood screws. The front can be made into a lift-up curtain form using greenhouse film or soft glass panels, for easy opening. Under the flower rack you can place several drip trays with some water below. First, it adds humidity; second, the water can store the heat of the day and release it slowly at night, preventing too rapid a drop in temperature at night when the sun cannot reach it. A metal flower rack can be fully wrapped and sealed with greenhouse film, and to enhance the insulation effect you can use double or even 4 layers. Everything else is the same as for a wooden flower rack.

A flower rack treated this way needs to be placed somewhere that gets sun during the day. Generally, on a clear day with an outdoor temperature of around 5 degrees, the temperature inside the enclosure can rise to around 25 degrees. At night, no matter how low the outside temperature is, because of the double insulation effect of the home environment, the temperature inside the enclosure can be slightly higher than room temperature. (Are there any students whose home room temperature is below 0 degrees? If so, please raise your hand, Old Ginger will help you organize donations of money and sweaters.)

The above methods are suitable for Haworthia and mesemb plants.

(2) How to create a temperature difference in summer

This topic is rather tragic. The sauna-like heat of the south gets in everywhere, and apart from air conditioning there seems to be no very good solution. Never mind the daytime; frying eggs on manhole covers happens every day. At night it is a bit better, at least outdoors it can be below 30 degrees, but indoors, the zero temperature difference of 30 degrees during the day and 30 degrees at night is very hard to change. You say there is air conditioning, but after all only a minority of homes have central air conditioning. With split air conditioners, at night only the bedroom has the air conditioning on, and you would not put the flowers in the bedroom, would you? Some students install small air conditioners in their flower rooms or even greenhouses. This is of course a good method. But if everyone did this, why would Old Ginger still babble on? After all, there are still more students who like to save money...

We have said that Haworthia is in deep dormancy in summer, which is the sign that the growing season has come to an end. Compared with winter dormancy, summer dormancy is a physiological cycle behavior, a controlled dormancy that allows the plant to accumulate the drive to grow in the next growing season, and for the plant this is relatively beneficial. So in summer, the purpose of creating a temperature difference is not growth, but maintenance. Appropriately enlarging the temperature difference during the summer dormancy period can prevent physiological disorders in the plant caused by high temperatures. It can also, through the relatively low nighttime temperature, let the heat accumulated in the potting soil during the day dissipate, thereby maintaining the health of the root system.

Therefore, the summer temperature difference mainly relies on lowering the nighttime temperature, letting the daytime take its natural course. As long as you do the shading work well, let it be whatever temperature it is. At night, without using air conditioning equipment, use physical cooling methods such as misting and electric fans to lower the temperature. Misting needs to be done until the soil surface changes color and the plant surface is covered with water droplets, then turn on the electric fan to blow air. Water evaporation can take away heat. The data Old Ginger measured using this method is - in the height of summer, after 8 pm, when the air temperature around the flower pots is 32 degrees, after misting and blowing air, the temperature can drop to 29 degrees within 1 hour. Then combined with opening windows for ventilation, or using the room air conditioner's airflow to share, the lowest nighttime temperature in the flower room can reach a level comparable to the outdoor temperature (around 27 degrees). For Haworthia to pass the summer in dormancy, this low temperature is sufficient.

The above method is only suitable for Haworthia plants. For mesemb plants, Old Ginger recommends not cutting off water in summer and just letting them grow freely. As long as they are healthy seedlings over 2 years old, the more sun the better they look.

(3) How to create a temperature difference in other seasons

In winter, mainly keep warm during the day; in summer, mainly lower the temperature at night. Then when the golden spring and autumn seasons arrive, the main approach should be getting close to nature.

Getting close to nature means making the cultivation environment's temperature difference close to the outdoor temperature difference. In spring and autumn in the south, outdoors there is a natural large temperature difference of about 10-15 degrees, plus fresh outdoor air and natural dew nourishment, and it would truly be a pity to waste it.

There is no need to say much about the methods here. Open windows for natural ventilation, electric fans for forced ventilation, open-air free-range growing, and so on. As long as the flower room becomes a pavilion, the goal is achieved. Of course, be on guard against the late spring cold and the restoration of the subtropical high mentioned earlier.

(4) The use of temperature difference

Once we have learned to create a temperature difference, we can use it to regulate plant growth. The specimen plants you see on Japanese websites, whether plump or short and stubby, are also the result of making heavy use of temperature differences.

For succulents, the few weeks before the theoretical dormancy period are the reproductive growth stage. During this stage the apparent growth is very weak, but the rate of nutrient accumulation within the plant reaches its peak. And the timing differs for plants of different families and genera - Haworthia plants show it in early summer, mesemb plants show it in late autumn.

During this period, enlarging the temperature difference can enhance the plant's nutrient accumulation, and the plant will become plump because of the increase in dry matter within its body. The thickening of stems and leaves can also correct the etiolation and legginess accumulated during the growing season. Combined with the slow growth caused by low nighttime temperatures, the plant will naturally show short and plump characteristics. Even enough temperature difference can offset the legginess caused by insufficient light, though Old Ginger has not tested this, just mentioning it in passing.

Furthermore, the temperature difference provides external conditions for the plant's flower bud differentiation. Plants regulated by temperature difference will bloom more uniformly and vigorously in the subsequent flowering period, with sturdier flowers. This is very beneficial whether for Haworthia hybridization or for viewing the flowers of mesemb plants. Just imagine a group planting of Lithops blooming together overnight. That feeling cannot be experienced without seeing it with your own eyes. (Students who grow Lithops should still choose group planting. Do not be so petty as to put one seed in one pot. Do not have that many, you say? Leave a message for Old Ginger, and Old Ginger will give you - seeds.)

Temperature difference is also very important for controlling the flowering period of Haworthia plants. I believe students who have hybridization experience all know that a pairing planned long in advance often cannot wait for one of the plants to bloom in time, and they have to give up. Fortunately, we still have temperature difference to use. Enlarging the temperature difference, especially raising the daytime high temperature, can promote the plant's flower bud differentiation. This is an unchanging axiom and needs no proof. By controlling the daytime high temperature, you can control the flowering time of Haworthia plants. The higher the daytime temperature, the faster the flower bud differentiation; otherwise the slower. In this way you can regulate and unify the flowering time of the plants you want to hybridize. For example: say you want to hybridize two Haworthia plants, one of which already has a flower stalk 30 cm tall, while the other has just barely emerged. Then hurry, throw the fast-growing one onto the windowsill and keep the other sealed in the greenhouse. After being kept sealed for a while, the flowering speeds become the same...

However, for Haworthia plants whose flowering periods are not even in the same season, the method of regulating temperature difference may not be so useful. Take the Haworthia retusa group as an example. Say the earliest to bloom is 'Kangping', which blooms in April, while the latest to bloom is 'Blue Crab', whose flower stalk only emerges in June. Such a gap is almost impossible to bridge by the temperature difference regulation of home cultivation. But presumably it can be done in a greenhouse; otherwise, that hybrid seedling of Kangping * Blue Crab at Old Ginger's home might have come from Mars.

In addition, using temperature difference can also control pests and diseases in the pots. Especially in spring and autumn, a suitably low nighttime temperature can inhibit the growth of bacteria in the pot and the activity of pests, with the ultimate aim of reducing the use of chemicals and achieving the goal of eco-friendly flower growing.

Temperature difference can also increase the thermal expansion and contraction of the granular planting medium, and through the soil's own physical changes, indirectly achieve the purpose of improving the soil.

In short, the rational use of temperature difference is the key to growing good Haworthia plants. If sunlight, water and planting medium are the staple food of home-grown plants, then the above 3 items can only solve the plant's basic needs, while a suitable temperature difference is a tonic that can let the plant move from basic sufficiency to a comfortable level.

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