Should I use Lavarocks or Expanded Clay?
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Contributed by: snoofer
Thanks to: Aiptasia, the colonel, Snaps_Provolone,
OzHornet, tdmaker, nuniabiz, Son-T, raygun, 10k
Images: Philcuisine and unknown
sand, perlite, rockwool, oasis cubes, coco, expanded
clay (?poprocks? or Hydroton/Groton/ L.E.C.A. and other
names), and lava rocks are common choices for Hydroponic
Lava rock and poprocks are popular as
they are inert, do not absorb water, provide good
aeration, are Ph neutral, and can be re-used.
Which is better?
Both of these
mediums have advantages and disadvantages, depending on
the system and requirements. Lava rocks work better in
some systems, poprocks in others. They are good for
drip, nft, flood&drain and for filling mesh pots.
Both types should go into a system that
irrigates frequently, as Hydroton and lava rocks are
non-porous and have little water-holding capacity. Both
types should be pre-washed and sterilized to remove dust
& mold. Lavarocks:
are a cheap and readily available medium. They are good
for large bucket grows where stability is a necessity.
(Aiptasia)"... consists of feathered basalt
which is pH neutral. Basalt can carry trace metals, and
my big lava rocks rust from the trace metals..."
(Snaps_Provolone) "Lava rock is chunks of red,
porous (VERY porous!) basaltic (volcanic) rock. I've
purchased it both by the bucketful, and by the bag at
any place that sells landscaping materials. It is much
lighter than, say, peagravel, but still rather heavy.
Only rockwool (MUCH more $ than lava rock) has
more air/nutrientfilm capacity. Lava rock has REAL good
capillary action too. Once wetted (I use flood-drain/ebb
flow), it holds VAST amounts of water, while affording
roots WAY more space to devolop than rockwool EVER can."
Lava rock is good for ebb-flow/flood-drain, or
top-drip systems, but can also be used successfully in
an airated standing solution.
I still prefer
Hydroton though, it stays moist longer and lacks that
sharpness that tends to be harmful to soft tissue.."
Heavy. Roots will become damaged if a plant shifts;
heavier lava rocks will help stabilize a large plant,
preventing it from leaning or shifting during growth.
Chemically inert and reusable. Does not absorb
Lava rocks ?lock? together to give a more solid and
stabile medium to plant in. Large plants are less likely
Easy to find, usually inexpensive
Lava rock come in large, medium and pellet sizes.
Individual rocks can be hand-placed to anchor air
stones, drip lines, stakes, etc. Stakes embedded into
the rocks will be solid.
Lavarocks can take a beating and not fragment or
Lavarocks need to be pre-soaked to clean them of
grit and stabilize the pH:
(raygun) "if you use the
lava rocks just make sure that you rinse well and soak
them in ph balanced h2o for 3-5 days then rinse and
Lava rocks are a pita to clean. They have irregular
surfaces and micropores that roots and bacteria love to
fill. 100% sterilization is never guaranteed. Some
growers consider them one-grow disposable.
colonel) "i find it easier to just buy new lavarock and
rinse/clean it all than to reuse it: scrub each
individual lava rock clean off all traces of root, and
then disinfect and then rinse real well to get all the
disinfectant chemical out.. but thas just me"
Lava rocks are heavy. This makes everything heavier,
harder to haul/move, and more expensive to ship.
Lava rocks may contain traces of heavy metals, which
may cause nutrient deficiencies and pH swings.
Irregular rock shapes provide uneven aeration and
wetting in the rootzone. Roots will be less able to
penetrate evenly throughout the medium
"I did not like using the clay by itself as it did not
disperse the ater from my drip tube and I ended up with
dry spots in my pots. The lava roxs are all shapes and
sizes which help change the path of the falling water."
More difficult to fill containers
Expanded clay / Hydroton
?Hydroton: This Lightweight Expanded Clay Aggregate
(L.I.C.A.) is manufactured exclusively at high-tech
kilns in Germany and is used as a soil replacement in
hydroponics. Composed of shale that is pelletized and
fired, Hydroton holds water extremely well and transmits
it effectively. The pellets are uniform in size and have
an attractive, natural appearance. Hydroton is
chemically inert, has neutral pH, is reusable, clean and
(nuniabiz) "clay balls at like 2800
degrees which expands all the little bubbles in the clay
making the surface area something on the order of 100
times greater theres for holdin more o2 and wicking more
The high temperature sterilizes
the Hydroton, but mold can still form in the bags due to
condensation and breaks.
"marble-sized orange/brownish balls you can get from
nurseries or hydro stores - often used in aeroponics;
Poprocks are the preferred medium
Expanded clay is much easier to clean. The round
balls of clay have a smooth surface coating that can be
cleaned of roots and bacteria.
Chemically inert and reusable
Different sizes available
Lighter than lava rock
Poprocks are more uniform in size & shape. They
can be poured into containers, and they fill containers
The round pebbles do not compress or touch. The
uniform space between the pebbles provides even aeration
and wetting throughout, allowing roots to fully grow
into the medium. The clay surface repels water, but
surface tension coats each clay ball in a thin coat of
water ? perfect conditions for roots. Cracked rocks
absorb water like a sponge.
The round pebbles have more surface area than the
flatter lava rocks, proving more area for roots to cling
Can be more difficult to source
Poprocks are round and as such are less stable to
plant in. Larger plants may shift if disturbed, damaging
their root systems.
Poprocks both sink and float! Poprocks can clog
drains and tend to go everywhere. Knock a pot over and
you?ll be picking up pebbles for a long time
Poprocks need to be thoroughly pre-washed to remove
the heavy clay dust that is caused by the balls rubbing
together during transport. Clay dust will still come off
them and may require a flush of the system upon startup.
Heavy clay residue will settle to the bottoms of systems
and may clog pump filters.
Poprocks will slowly break down, as they are exposed
to acidic nutrient conditions.
Poprocks can break, shatter and become crushed with
Rinsing tip for both lava and pop
(tdmaker) ?Simply, poke holes in the
bottom of the bag and cut open the top. With a water
hose, run water through the top of the bag. The red
powder will flow from the bag through the holes in the
bottom. Oh, and do this outside. Otherwise, do smaller
Should I sterilize my used
medium or encourage bacteria?
(10k) As far
as harboring beneficial bacteria, user 'Jackerspackle'
wrote some extensive material on this several years ago.
Basically what he said and I believe and
practice, is that expanded clay mediums harbor them too.
Just dont sterilize your rockage when washing them out
and you'll have plenty remaining in and on the medium to
replenish the next grow as soon as they're rewetted.
Bactors like nitro simmonas and nitro bactors can go
dormant in a dried out state, but will become "alive'
again as soon as they're moistened. Of course, you'll
keep a more robust living culture going if you dont
allow the used rock to ever dry out completely.
The only time when a grower would really want to
sterilize the rocks is if he had suffered a root disease
in the previous grow. A gnat infestation is NOT a good
reason to sterilize the rocks since they can easily be
treated using BTI bacteria and semi-sealing up the
wetted bag (or tub) full of rocks for a week or so to
prevent the life cycle from any possibility of
continuing, but keep an air stone running in the closed
up wet bag or box of rocks to help keep the bacteria
| Last modified: 16:19 - Dec 29,