LECA Preparation
You wouldn’t want to live in a room filled with trash right? Well, your plant doesn’t want that either. It all begins with prepping your LECA.
Why?
LECA is made by taking pre-treated clay and firing it in a rotary kiln at high temperatures, and then cooled down. The end result is a light-weight expanded clay aggregate (LECA) that 5x it’s size during this process. The “pre-treatment” of natural clay is somewhat of a mystery but it likely involves chemicals and binding agents, where when in contact with heat, causes the clay to expand and form into little balls. During the firing process, likely some of the chemicals become inert or is evaporated, but there is definitely “stuff” or “crud” or “trash” inside these LECA balls. Furthermore, after these balls come out of the kiln, they are doused in cool water to reduce the temperature, but what’s in this water?
“But I just give it a rinse and use it, and my plants are fine!” — Says a lot of people on the internet. Sure, I can also live in a house with a bunch of trash too, but I’m not going to be happy about it!
Treating LECA before you use it is generally a good idea, so your plant can begin it’s Semi-Hydroponics life with a healthy start. If LECA isn’t soaked properly it can cause a plant to grow a lot slower than it should. Over the past year of LECA growing, I’ve also noticed well-soaked LECA requires a lot less flushing than not-soaked LECA. If you are a lazy LECA user, make a conscious choice on how you want to be lazy here. For me, a few days of foresight is entirely worth not having to flush weekly.
Step 1: Rinse the LECA
Take the LECA out of the bag and give it a good rinse to get debris and clay dust off.
Protip: I use a mesh laundry bag and my garden hose and do this outside. Try to not get clay dust down your drain, it’s not great for your pipes.
Step 2: First Soak
Soak the LECA for 24 hours using tap water / hose water. This first soak will get the first wave of the crud out of the LECA.
For extra lazy mode, just let the first soak go on for2+ days and now you can use your LECA! (If you want to be extra lazy you have to be patient.)
Protip: I take the laundry bag full of LECA and soak it in a large plastic container. For 50L of LECA I can fit it all into two mesh laundry bags.
Science Stuff: You can observe the PPM of the soaking water after this first soak. (For a PPM primer, see my nutrient solution guide). My tap water is around 150PPM, and after 24 hours of soaking, Hydroton LECA measured at 800PPM. Compared to a fertilizer solution that sits at 300PPM, that is a lot of extra crud in the water. Imagine if you didn’t soak, your nutrient solution is 1/3, and unknown chemicals is the other 2/3. Gross.
Step 3: Second Soak
Dump out the soaking water and replace with fresh tap water / hose water. Soak for an additional 24 hours. After this soak you can use your LECA! However for high-value plants where you want to make sure they have a great start, read on.
Science Stuff: The second soak usually results in about 300 - 400PPM after 24 hours. Remember in high school science class where you learned about the Law of Chemical Equilibrium? Yeah no me neither. But basically when you put your LECA (product) together with water (reactant) the water and chemicals within the LECA wants to be at equilibrium with the water outside of it until it’s equal inside and outside. If your water is at 100PPM and your LECA is at 800PPM, over time your water will measure higher in PPM and your LECA will measure lower in PPM. The reason for the second soak is to speed up the process. Soaking 800PPM LECA in water that is 100PPM versus 400PPM, the 100PPM will go a lot faster, and the equilibrium point will be lower.
Step 4: Dry and Store
Drying and Storage is recommended if you’re not going to use the LECA right away. You can dry the LECA in the mesh laundry bags, they allow for amazing airflow! If you plan on using the LECA right away, you can skip this step.
Protip: I will do Steps 1 - 4 in the summer outside for all the LECA I plan to use in the winter. Also if you leave your LECA outside and it rains, that’s a double win because mother nature is rinsing your LECA for you! But remember to bring those mesh laundry bags indoors after you’re done, mine are now broken because critters wanted to see what was inside.
Step 5: Third Soak
An additional soaking is not a bad idea, especially for high-value plants. If I’m doing this step, I’m using filtered / reverse-osmosis / distilled water at 0PPM.
Some prefer to soak LECA for over 2 weeks before use. This is also a good idea if you’re using cleaned, dried LECA from previous steps. You always want to use LECA that’s been soaked and wet, never dry.
You can also add CalMag (Calcium Magnesium supplement) to the soaking water, as well as any rooting hormones like KLN. Adding these supplements can happen as early as the first soak, as the Ca and Mg ion substitute for the less desirable soluble minerals in the LECA.
Protip: I have two buckets that are always filled with LECA sitting in CalMag and KLN. Sometimes they will soak for a few weeks before I use it up.
Science Stuff: Why shouldn’t you use dry LECA? It’s because LECA wicks water very effectively. If you have roots come into contact with very dry LECA, it will wick water away from the roots and can cause the roots to desiccate. Always make sure they are well soaked before use.
But wait, don’t I have to boil?
You can boil LECA if you want to. I would recommend after the 2nd soak. However I find it tedious and not necessary because I find the idea of boiling something that’s been through a rotary kiln entirely redundant. Perhaps for those high-value plants, might as well give it a good boil to sterilize, but I usually skip this step for LECA straight out of the bag, as I have other ways of dealing with organic intruders such as mold, fungi, or bacteria.
If you are reusing LECA, please DO boil it. I will publish a guide to reusing LECA at some later time.
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