In Search of a Good Soil Recipe

 Over the last several years I've tried to find or create the optimal potting soil for growing Aloes and Agave. The premixed soils I bought from landscape supply yards didn't work out - even the so called "succulent mixes". They were too sandy and heavy or contained too much wood mulch (which I'm pretty sure ended up leaching nitrogen from the soil). Everything seemed to have drainage issues over time as finer components of the soil were washed toward the bottom of the pots - which led to water-logged roots. I've also noticed different soil compositions used in potted plants from other nurseries. Some prefer a large percentage of coconut coir which seems to keep the soil too moist.

There is a lot written online about the best succulent mix but nothing I could find that referred to a practical test of different soil compositions. It's time to put on those high school lab coats and test our way to an answer.

Below are some of the soil components I used in this test:

Coconut coir

Sandy Loam

This "sandy loam" actually contains a fair amount of wood mulch and is in truth part of an older soil delivery. The mix was always too sandy / heavy so I've ended up using it as an amendment. I think part of the problem with this mix was the sand was too fine which inhibited drainage.

Organic Amendment Mix

 

The Organic Amendment Mix from Lyngso is a blend of Organic Green Waste Garden Compost, Redwood Sawdust, and Organic Feather Meal. It's supposed to enhance soil moisture and aeration. Feather meal is high in nitrogen which isn't ideal for Aloes but at the same time redwood sawdust temporarily removes nitrogen from the soil as it breaks down.

Perlite

 

I've noticed that soils with lots of organic materials will change over time as they are decomposed by bacteria, earthworms etc. This seems to lead to compaction of soil toward the bottom of the pot and reduced aeration. Needless to say succulent roots don't like poorly aerated soil. Inorganic components, like perlite, do not make good worm food and are much lighter than alternatives such as coarse sand, crushed volcanic rock etc.

The Soil Mixtures

Here's a quick run down on the various soil recipes I used.

Soil Mixture #1

 

 

 

 

• 4 parts perlite
• 3 parts amendment mix
• 1 part sandy loam mix

 

Soil Mixture #2

• 2 parts perlite
• 1 part coconut coir
• 1 part green waste garden compost

Mixture #2 above is my guess at what might make a good soil for a variety of Aloes. 50% perlite for drainage and aeration, 25% green garden compost as a fertilizer and 25% coconut coir to help hold onto moisture. I suppose the drawbacks of this mix might include: too much moisture retention and too many available nutrients leading to fast, top heavy growth that is prone to disease / pests. 

Soil Mixture #3

• 1 part perlite
• 1 part 1/4 fir mulch
  
• 1 part sandy loam mix

I'm not really sure what to expect with this mix... good drainage and lower available nutrients might be a win or a total fail. So much fir mulch makes me nervous.

 

Soil Mixture #4

• 2 parts perlite
• 1 part green waste garden compost
  

This is the simplest mix at 66% perlite and 33% garden compost.

Soil Mixture #5

• 2 parts perlite
• 1 part amendment mix

66% perlite and 33% amendment mix which is itself a mix of compost and redwood sawdust.

 

The Plants

For the test plant I chose the humble Aloe "Blue Elf" which is a commonly used, resilient,  landscape plant ( plus I happened to have several flats available for the test). I don't believe it has unique needs that might bias the results - so seems a decent test subject.

Aloe "Blue Elf" starts

The above plant-lets started life via tissue culture in a lab and should be genetically very similar (which is also great for the test)

Mixture 2 newly planted

Each flat contains 16 x 4 inch nursery pots all using the same soil mixture.

Mixture 3 newly planted

I'm not sure the above soil mixture will work very well - but it's the nicest looking.

Mixture 4 newly planted

 

I did my best to get all the test plants into soil within a relatively narrow time period - a few days. Typically, Aloe "starts" like this may need to be up-potted within 6 - 12 months - just depends on the species. Hopefully the results will be obvious much sooner.

Let me know what you think. Which soil do you think is likely to create the healthiest plants? What other soil combo's should I have tried? I'll follow up in the next several months with the results by looking at the differing growth of plants both above and below the soil line.

Until next time - happy growing.