Poor Soil Aeration/Drainage and Anaerobic Decomposition

[JS671]

I’ve read on this forum that potting soil for palms needs to drain well and have adequate aeration via not using easily compacted materials and not using materials with small particle size (which usually compact easily anyway). The main reasons are that poor aeration and drainage cause root rot and prevent nutrient uptake. I was wondering if anyone knows if anaerobic decomposition of organic material (e.g. peat moss, coco coir, compost) contributes to poorly draining soil being suboptimal for potted palms (perhaps due to decreasing ph or pathogenic microbes?). I’m curious because I’ve seen many species of palms growing in volcanic clay here on Guam and have potted many seedlings in poorly draining mixes ~30% clay (from my yard), 30% coarse sand, 20% perlite, 10% peat moss, 10% compost. I’m going to adjust my mix and add more perlite for my next batch of Bismarck and triangle seedlings, which don’t enjoy my current mix as much, and compare the groups over time. I’ll continue testing different mixes on different species but am particularly curious about the anaerobic decomposition of organic material in poorly draining mixes because I haven’t been able to find any helpful information on that topic.

Thank you

 

[Silas_Sancona]

35 minutes ago, JS671 said:

I’ve read on this forum that potting soil for palms needs to drain well and have adequate aeration via not using easily compacted materials and not using materials with small particle size (which usually compact easily anyway). The main reasons are that poor aeration and drainage cause root rot and prevent nutrient uptake. I was wondering if anyone knows if anaerobic decomposition of organic material (e.g. peat moss, coco coir, compost) contributes to poorly draining soil being suboptimal for potted palms (perhaps due to decreasing ph or pathogenic microbes?). I’m curious because I’ve seen many species of palms growing in volcanic clay here on Guam and have potted many seedlings in poorly draining mixes ~30% clay (from my yard), 30% coarse sand, 20% perlite, 10% peat moss, 10% compost. I’m going to adjust my mix and add more perlite for my next batch of Bismarck and triangle seedlings, which don’t enjoy my current mix as much, and compare the groups over time. I’ll continue testing different mixes on different species but am particularly curious about the anaerobic decomposition of organic material in poorly draining mixes because I haven’t been able to find any helpful information on that topic.

Thank you

 

In a nutshell, yes, decomposing organic components in a soil mix can contribute to anaerobic conditions that lead to root rot, etc issues.. As Organics decay, their particle size becomes smaller. More of it in a soil mix means it layers upon itself filling more and more pore space which, when left open,  would allow oxygen to circulate through the soil.

Less oxygen +moist/ warm environment = better conditions for microbes that thrive in those conditions.. Because they're using up what little oxygen is able to circulate through the soil, plant roots are suffer and begin to decay, which invites even more microbes in to cause more decay.

That said, some organics are worse than others... and some palm species / other plants will respond differently to a soil mix high ..or low in organics  based on where they originate / what soil conditions they evolved with.  Some species will handle a thick, mucky soil better than others. 

Palms from drier areas of the world often want lots of oxygen moving through the soil column, which is why they grow in soil that is rockier / contains lesser amounts of organics rather than in places where the soil particle size is smaller / denser.   On the other hand,  Throw some leafy tropical groundcover-ish thing, or bog grower that evolved to grow where the soil is wet/ dense and full of organics in a well- draining and chunky " Cactus mix " type of soil, and you'll likely kill it fairly quickly..

Palm species that grow near ..or in water are often able to tolerate soil that is much denser / of finer particulate size / much higher organic content.

Peat Moss is notorious for breaking down fairly fast, especially in wetter areas. As it does, it becomes muck which compacts. This is made worse if peat moss is combined with soils derived of Limestone / Marine sediments.. ...due in part to some sort of Chemical reaction that occurs between the two..

Compost can do the same, though it often will clump a bit more / not break down into soupy mucky stuff quite as quickly unless constantly soaking wet.

Coir / Coconut Peat takes much longer to break down into finer particle size since ..and, i could certainly be wrong on this.. there are natural compounds in the material itself that i believe slows down the breakdown / decaying process.

Out in nature, you'll likely notice that the Organic layer of the soil column in a road cut/ hillside sits on top of a more mineral / organics- free base ..where a fair amount of a root zone is.  In some areas, the two soil horizons may blend well so that the difference between each is gradual. In other places, the different layers are quite obvious. Regardless, organics / benefits of the organic layer are getting to the parts of the root system that is growing in the soil layer that is more mineral / contains less organics. At the same time, the soil below the orgainc layer drains freely enough that oxygen penetrates and circulates through it.

Not the easiest to duplicate in a container of course, but.. For example, i don't use peat Moss ..at all.. Instead using Cocopeat ..and maybe some decaying leaves or compost as my " organics ". A combination of a product called Turface MVP / AKA Seramis in other parts of the world, Pumice, Crushed Volcanic lava rock, and/ or Granite grit i collect from a nearby wash make up the inorganic half of my soil mixes  ..adjusting the ratio of each ingredient based upon what the plant grows in in habitat..

I don't use a " one size fits all " soil mix for everything, ...or perlite / wood chips.. Perlite is too light and will gradually work it's way up and out of the soil mix, leaving behind a denser, more compacted soil mix..  Wood chips may help with drainage for a little while, but can cause problems as they break down later.  Experienced the bad effects of both materials myself a few times.

One thing of note: there are certain circumstances where certain plants/ palms evolved to grow in soil derived from certain kinds of rock that possess higher ..or lower concentrations of X elements / nutrients.  For example, plants that evolved to grow on limestone/ marine derived sediments may not do well in a soil mix that contains ingredients that make it more acidic,  or vise versa.

I myself try as best as i can to take that aspect into account when mixing soil for specific things as well.

Hope this helps..

[PalmsandLiszt]

17 hours ago, JS671 said:

The main reasons are that poor aeration and drainage cause root rot and prevent nutrient uptake.

17 hours ago, JS671 said:

I’m curious because I’ve seen many species of palms growing in volcanic clay here on Guam and have potted many seedlings in poorly draining mixes

I think the main reason why people go on about well-draining media for potted palms is that a lot of them are growing in suboptimal conditions with too low light/temperature/humidity; people who have optimal conditions outside tend to plant them out and don't keep them in pots for long. Similarly, they will grow better in pots in less well-draining media the more optimal the conditions are, such that the roots can out-compete the various microorganisms in the soil for the available oxygen. In Guam you can probably get away with much more poorly-draining mixes than I could up in the (not quite yet) frozen north because the plant isn't going to slow down for other reasons.
Also, the right size of pot matters, as water will collect in areas of a pot and possibly promote anaerobic activity in a way it won't in the open soil, so you want a pot small enough that the palm's roots will quickly be able to predominate, and water added goes straight to the palm rather than festering.

[JS671]

On 10/15/2022 at 2:07 AM, Silas_Sancona said:
Out in nature, you'll likely notice that the Organic layer of the soil column in a road cut/ hillside sits on top of a more mineral / organics- free base ..where a fair amount of a root zone is.  In some areas, the two soil horizons may blend well so that the difference between each is gradual. In other places, the different layers are quite obvious. Regardless, organics / benefits of the organic layer are getting to the parts of the root system that is growing in the soil layer that is more mineral / contains less organics. At the same time, the soil below the orgainc layer drains freely enough that oxygen penetrates and circulates through it.
 

That’s the interesting thing that made me think using clay wasn’t too big of a deal for most of my palms because I’ve seen royals, bismarcks, different species of Phoenix palms, triangles, livistona chinensis, and saribus rotundifolia grow decently in the soil on my island. For the most part there’s not much organic matter found in the topsoil, then the subsoil is almost exclusively clay, and the third layer is highly weathered volcanic rock that the clay was formed from (this is the case for the southern half of the island). I suspect that once many of these palms are a bit more mature and out-planted they can handle the lack of air and compaction. For my plants from drier climates with more soil aeration I’m definitely gonna cool it on the clay I use for my mix haha.

On the northern half of Guam there’s usually a layer of clay (either from limestone or volcanic rock) mixed with organics on top of pure limestone. This coincides with your observation of soil horizons you pointed out and I definitely noticed that many of the palms I see up north are usually doing better than the ones down south. It seems that as long as there’s plenty of organic matter in the clay though, that many of the palms are happy.