Amendig soil in the garden with Perlite

[Palmfarmer]

Have a small area in my garden I want to put my dyckias and cactus, agaves etc. however it does not drain well enough. If I dig down 40 cm I will reach a sandy soil that drains well. So I was thinking of making a 40 cm deep hole then amend with perlite and backfill. Perlite is good for the job or should I use Sand instead? I got perlite, compost, coco coir and peat moss at hand, but I can obtain sand if it is needed. 

Edited September 17, 2022 by Palmfarmer

[Silas_Sancona]

4 hours ago, Palmfarmer said:

Have a small area in my garden I want to put my dyckias and cactus, agaves etc. however it does not drain well enough. If I dig down 40 cm I will reach a sandy soil that drains well. So I was thinking of making a 40 cm deep hole then amend with perlite and backfill. Perlite is good for the job or should I use Sand instead? I got perlite, compost, coco coir and peat moss at hand, but I can obtain sand if it is needed. 

Grit/ gravel... NO perlite... it will float away.  Best " sandy" stuff you can use comes from  a creek / river bed, etc.  40cm / 15 inches isn't really bad.. you could just turn it over and mix the better draining stuff with the finer- grained soil that sits at the surface.. Most Cacti/ Agave, etc that grow out in the wild often grow in soil that is finer grained at the top, and better draining/ containing more rock, etc deeper down where roots would penetrate.

As long as any standing water that might pool around the plants is drained off within a few hours after it collects, it will be fine. 

[Merlyn]

I created a raised bed area here in Florida with a mix of native sandy soil, generic "topsoil" (shredded tree scraps), Sakrete Paver Base (crushed limestone gravel), old freebie sandbags they give out from hurricanes, and perlite.  This works fine with the 40-60 inches of rain here, the perlite doesn't wash away as long as you cover it with gravel.  In my case I used either red lava rock or salt-and-pepper granite as a topper. 

I would not recommend coco coir, it retains way too much water.  For drainage small gravel is ideal, and lava rock and expanded shale are very good at allowing drainage without holding too much water.  I found this experiment done by a bonsai guy, he soaked the materials in water and then drained them and weighed the before and after.  Coco coir held about 85% of the water, while granite at the other end only retained 5% of the water.  I'd think maybe 25% organics and the rest a combination of gravel, lava rock, maybe perlite or Turface MVP (or similar fired clay pebbles) would drain reasonably well.  I'd avoid vermiculite because it disintegrates over time.  Fine sand is a bad idea, but you could do ok with what Silas recommended, i.e. coarse riverbed grit.

Coconut Coir	14.6%
Akadama	26.7%
Kanuma Pumice	29.0%
Diatomaceous Earth	30.2%
Compost	31.6%
Pine Bark	33.3%
Turface MVP – LECA	36.2%
Perlite	36.4%
Commercial Peat Moss	40.0%
Vermiculite	41.7%
Sand – coarse grit	67.6%
Lava Rock (Scoria)	76.5%
Expanded Shale	84.6%
Granite Chips	94.4%

[Palmfarmer]

55 minutes ago, Merlyn said:

I created a raised bed area here in Florida with a mix of native sandy soil, generic "topsoil" (shredded tree scraps), Sakrete Paver Base (crushed limestone gravel), old freebie sandbags they give out from hurricanes, and perlite.  This works fine with the 40-60 inches of rain here, the perlite doesn't wash away as long as you cover it with gravel.  In my case I used either red lava rock or salt-and-pepper granite as a topper. 

I would not recommend coco coir, it retains way too much water.  For drainage small gravel is ideal, and lava rock and expanded shale are very good at allowing drainage without holding too much water.  I found this experiment done by a bonsai guy, he soaked the materials in water and then drained them and weighed the before and after.  Coco coir held about 85% of the water, while granite at the other end only retained 5% of the water.  I'd think maybe 25% organics and the rest a combination of gravel, lava rock, maybe perlite or Turface MVP (or similar fired clay pebbles) would drain reasonably well.  I'd avoid vermiculite because it disintegrates over time.  Fine sand is a bad idea, but you could do ok with what Silas recommended, i.e. coarse riverbed grit.

Coconut Coir	14.6%
Akadama	26.7%
Kanuma Pumice	29.0%
Diatomaceous Earth	30.2%
Compost	31.6%
Pine Bark	33.3%
Turface MVP – LECA	36.2%
Perlite	36.4%
Commercial Peat Moss	40.0%
Vermiculite	41.7%
Sand – coarse grit	67.6%
Lava Rock (Scoria)	76.5%
Expanded Shale	84.6%
Granite Chips	94.4%

Thanks for the information. Got a offtopic question can I plant a Coconut in clay soil and it will do well? If not can I just amend with compost and mound plant it? Its a funny experiment. Will keep the trunk wrapped with burlap and twirl c9s or c7s all around the fronds once christmas is approaching. 

[Merlyn]

Unfortunately I know nothing about growing plants in clay.  I have some experience killing coconuts in my front yard any time it got below 30F... 

[D Palm]

I bought like 5 bricks of cocoa fiber for 50 cents a brick years ago. Used it as a back fill for my first Bizzy. It never complained.

I used it for pots, it did drain well but holds 0 nutrients unfortunately. I almost never see it now at retailers.