Microclimate and its role in maintaining succulents

A portion of my succulent growing area that is exposed to full sunlight. Mature plants, divisions, and cuttings live side by side. Note how most of the plants are over-potted.

Most of us tend to think of climate as atmospheric conditions heavily influenced by the change of seasons and, in the tropics, the effect of trade winds. But climate and knowledge about it is a generalization that only applies to a large set of areas or regions, and is really useful to the gardener in a limited way. A microclimate on the other hand refers to conditions that prevail over a small area and often very different from the general climate. There are many variables involved, including the proximity of a body of water, the presence of hills which affect the angle and incidence of sunlight, soil type, and vegetation. The microclimate present in your local neighborhood may be slightly different from one that is just a few blocks away- even though you share the same climatic conditions.

A tropical climate can be particularly challenging to a succulent gardener, where plants can be exposed to heavy torrential rains or extremely high temperatures particularly from the months of March to May, where rains very seldom happens, if at all. On the other hand, there are climates that are characterized by a very weak differentiation between dry and wet, such as on the eastern seaboards of the Philippines, where rains can fall at any time of the year and a so-called dry season is markedly absent. We cannot manipulate the climate to suit our plants, many of which came from South Africa which experience climates that aren't tropical, but microclimate can be controlled, to some degree. And for the purposes of this post, we will be discussing microclimate and the maintenance of succulents in the context of the drier and hotter months.

The variables 

We begin by looking into the variables mentioned above: the proximity of water, the presence of hills or similar land forms, soil, and vegetation. There are a few other factors, such as the direction your garden is facing, but since there is not much a gardener can do if it is facing either the north or south, then it seems prudent to not discuss it.

1. The proximity to a body of water.

We all know what evaporation is, and evaporated water adds to humidity. And depending on the month of the year or how thickly vegetated your area is, all that evaporated water can translate into some form of precipitation. But what does it have to do with succulents (and when I say 'succulents', it also include cacti, which are also succulents)? Notice that there are succulents that do come from the tropics of Africa: the commonly available Monadenium ellenbeckii and M. ritchei as well as the stapeliads Huernia keniensis and the various forms of Orbea semota all hailed from, or can be found on, Kenya, right smack in the equator, and there are otherwise arid-inhabiting cacti from the Americas that do experience heavy rainfall in their habitat, even though strictly not in a tropical climate. And even without the subject of rainfall, the proximity to a body of water brings about two factors that are important in the cultivation of succulents: breezes and the lowering of temperatures that come as a result of it. Constant air movement assists in the rapid evaporation of water you used to quench your plants earlier today, but that is assuming that you are using the correct soil. Your soil may be fast-draining, but if it is heavy on sand, then that medium is retaining water far longer than what you would expect. If your soil is composed of organic matter or commercially produced ones that are biodegradable, and air movement is not up to par, then rotting of your plants' bases will be the norm (a common stumbling block of neophyte keepers is the soil they use). The lowering of temperatures brought by breezes likewise bring respite during cloudless skies, as passing wind are always cooler than the surrounding temperatures- this phenomenon is what we call the windchill factor. Naturally, the same breezes blowing from near bodies of water further lower the nocturnal temperatures, in fact, a few degrees lower than from areas adjacent to it but already some distance away from the said body of water. Why does it matter to succulents that are otherwise used to high temperatures, you might ask. And the answer is that because many cacti and succulents are subtropical, and you will need to ensure that temperatures do not reach high levels month after month, and year after year. Granted, succulents in the wild are adapted to high diurnal temperatures, but it gets pretty cool at night. All plants, not just succulents, need that temperature drop or they will not thrive. In many instances, a few degrees' nighttime drop is not enough.

On the other hand, constant air movement also lowers the humidity, and this poses a risk to the plants when temperatures are especially high. However, this is compensated by the saturated air so there is really not much to worry about. Still, you may need to further the amount of moisture in the air, particularly at night. Keep in mind that in the wild, precious water is often delivered to succulents via mists and dew. Look at the ribs of cacti, as an example. It serves a function, and that is to channel whatever little water is available- very often from dew- down to the roots. Additionally, misting at night results in an effect called evaporative cooling, where the plants receive cooling from water evaporating from their bodies during the course of the night. I have a theory that the spines in the more wicked and ferocious-looking succulents serve more than just protect the bearers from herbivores and the blazing sun, but also capture mists and dew which cool the concerned plants as the moisture evaporates. Just don't be too trigger happy with the hand sprayer or you may end up saturating the medium.

View from the mountain range above our barangay with the expansive Laguna de Bay. Mt. Makiling, shrouded in atmospheric mist, looms in the horizon.

2. The presence of hills or similar land forms

If you are near one, then chances are that your place is receiving higher levels of light due to sunlight being reflected from those hills or mountains. And that is good for your succulents. But at the same time, heat is reflected too, but its effects are nullified by breezes coming from the slopes- assuming that the hills or mountain is still forested. If the slopes have depauperate vegetation, breezes are unsaturated and therefore contributes to an over-all lowering of humidity which is not good during the dry months. Generally however, nocturnal temperatures are lower if you live close to these land forms. Please refer to Number 1 on how to further lower the ambient temperatures at night.

But what if you dwell in the cities where instead of mountains, you have houses and other buildings dotting the neighborhood? This now presents a problem because all that asphalt from the streets and concrete from man-made structures absorb heat and release it slowly during the course of the night. This explains why it is frequently very hot in tropical cities. Your succulents may do fine under the sun, but plants do also need to rest, and that period of rest is dictated not just by the presence of sunlight, but by temperatures as well. When temperatures are still high come nighttime, your plants have to work overtime metabolizing and processing sugars. In the long run this can affect the over-all health of your plants, often by stunting, or rendering them weak and vulnerable to attacks by soil-borne pathogens or pests. This risk is amplified if you are using improper soils. In addition to fine misting at night, you may need to install fans and keep them operating all through the night.

A portion of the Sierra Madre as seen from my rooftop.

3. Soil

If you are located near the sea or have limestone-dominated prominences, then chances are that humidity is low due to the highly porous properties of limestone and sand. Add to that the frequent breezes blowing in from the sea, and everything dries up pretty fast. During the rainy season that is fine, but that same porous property can be a liability during the drier and hotter months of the year. The predominance of concrete in urbanized areas operates in the same manner, which should come as no surprise considering that concrete is sourced from limestone. In more or less urbanized locales, both precipitation and humidity can be lower than in rural settings.

4. Vegetation

The great majority of plants transpire during the day, and that moisture has a cumulative effect in raising humidity. Therefore, if there is very little vegetation around, then it can be very hot and that heat is made worse by dry air. And, if you live in a heavily urbanized setting with very little vegetation around the neighborhood then make no mistake about it, your plants can have a difficult time.

Alright, you may have been keeping succulents for a long time now and they are doing fine in spite of the less ideal microclimate, in fact, fine enough to be the envy of those with far less experience and years behind them. But that may just be an illusion from a false perspective simply because there is no one to compare your plants to. If you divide a plant and gave the division to someone with better microclimate and wait for let's say 5 months, chances are that the differences in health and growth between the two would be so obvious it can be almost embarrassing.

What you can do

At this juncture some of you may have noticed something: that all four variables are interconnected to one another and that these are just parts of a bigger whole, but crucial nonetheless. Air saturation is essential, as well as frequent air movement, and their combined influence is particularly beneficial during the hot months.

To lessen the effects of the sun, most people just resort to using overhead nets to cut back the light that the plants receive, but in my opinion, that is already going against the grain of what these plants are used to getting in the wild. Remember though that that is just a personal view. I see nothing inherently wrong in using such overhead protection. Alternatively, one can use polycarbonate sheets, but the Achilles heel of these products is their sensitivity to ultraviolet radiation, which eventually results in their discoloration. Whichever you choose, be aware that overhead shading is not enough.

People who keep other plants aside from succulents have one distinct advantage: they can maintain humidity simply by way of watering their other plants. If these 'other' plants are numerous enough and placed close to one another then there is a reliable source of humidity around. During the drier months I place shallow trays filled with gravel on some of the plants where water accumulates after watering. Since these trays are shallow and moreover filled with gravel, mosquitoes have a very difficult time proliferating in such receptacles, particularly if watering is done very often, where water accumulated from the previous watering is spilled over.

But what if personal preferences or space constraints place the keeping of other plants out of the question? The second best thing would be to use the tray method but position the pots of your succulents on a pedestal so that these pots are not in contact with the moist substrate and keep the media dangerously moist for extended periods. The photos below illustrate this concept:

Evaporating water contributes to humidity around the plants. Note that I do not employ this method since I have already struck a balance of cultural conditions among my plants, and for the purposes of these photos, I just used whatever is at arm's reach.

If you resort to that approach, you have to make sure that the pedestals (in the example above I of course used upturned pots) are stable and leveled, or the plants may come tumbling down on one another. And keep out the cats!

In the first photo above I drew attention to my over-potted plants. Over-potting succulents is something I have been advocating, apart from using mineral mixes, and for good reason. In other types of plants, over-potting is discouraged because the medium stays wet for extended periods which exposes the roots to risks of rot, especially since in these cases, a heavily organic mix is often the default medium. But in succulents, water-logging is a non-existent issue unless the mix used includes compost or other biodegradable soil. An over-potted plant have better root development and repotting (which of course disturbs and damages the roots) can be kept to a minimum, if at all. Additionally, a larger container provides better insulation and gives more stable conditions around the roots than if you were to use those teeny-weeny cute containers. So over-pot your succulents and use a mineral mix.

Lastly, allow me to discuss a very rarely given advice, but which is pretty standard in orchid and Nepenthes culture, and that is to choose plants that suit your general climate. Echeverias and sempervivums are very attractive, particularly to beginners, but many species from these two genera come from higher altitudes, and in the case of the latter, also from higher latitudes. If one lives in hot, low lying areas, then keeping these plants healthy can be frustrating, especially for the uninitiated. Unfortunately, and this is based from observations particularly in the Philippine scene, so many people resort to buying a plant they fancied and then ask other people how to take care of their new purchases which strikes me as rather irrational. Ideally, research on the plants' provenance and culture is undertaken before actually purchasing one. But there are also numerous occasions when the sellers do not know the names of the plants they are selling, in which case the buyer should make an effort to know about their names so that proper research can then be undertaken after they have taken the plant/s home. Alas, instead of asking about their newly bought plants' names, they ask for their proper care. Talk about spoon-feeding. What confounds the situation is when common names are instead given and the one asking settles for it. The problem with common names is that many different epithets can be applied on a single plant, depending on where one is, but that is also dependent on the whims of the person giving that name, which is usually a reflection of that person's ignorance on a particular plant's name. There are instances when research on a plant's cultural requirements are hampered when a whimsical common name is circulated instead of its universally accepted scientific name. Still, there is what we call 'zone denial'. Gardeners from more temperate areas know what this is. To illustrate, it's like wanting to keep a cactus when one is in Alaska. Of course, heaters and greenhouses can allow the cultivation of these plants, but many gardeners in the tropics, perhaps due to some limiting factor, are unlikely to put up a greenhouse designed to pull temperatures lower. And it is for this reason that a path of least resistance is better taken- choosing plants that suit your climate, instead of placing more premium on a plant's aesthetics, and then blindly hoping that it will prosper. Then again I may only be day-dreaming.

These pages from Acta Succulenta depict two species of sempervivums in their montane habitat. Acta Succulenta can be downloaded here: http://www.acta-succulenta.eu/

Have you been paying attention? Let us enumerate in brief what you can do to adjust your microclimate (alright, we can call it the micro-microclimate because we are only concerned here of your garden area) and pull your plant through the dry season:

1. Fine misting at night
2. Deployment of overhead netting or the like (optional; I only use nets for my other plants)
3. Use fans
4. Maintain lots of moisture-loving plants (optional but recommended)
5. Do the tray method
6. Over-pot your plants, and most importantly:
7. Do your research and determine which plants can prosper in your location before buying anything, and be realistic

Till then!

A fisherman casts his line while Sully the Jack Russell frolics around in the shallow waters. Laguna de Bay, the largest lake in the Philippines, is just a few minutes' walk from where I live.