Building Soil in Hawai’i: The Ultimate Recipe


Hawai’i is a lush jungle paradise.  But lurking underneath all that bounty lies a thin layer of soil that at times, just isn’t enough.  Many spots only have lava rock to grow on. Others are dealing with badly degraded soils from years of abuse by the plantations.

So how do we build soil in Hawai’i?  What is that magic formula that will create the black gold that grows abundant vegetables every time?

When building soil for raising vegetables in Hawai’i, I suggest a mix composed of the following: homemade compost, mac nut compost, worm castings, 6 month old mulch from the Green Waste center, composted manure, lime, and kelp meal.

Now that is a steller soil mix, but it’s not always possible.  That is a LOT of material you need to come up with before you even get to grow any food!  Lucky for us, that is not the only way. Let’s dive deeper into Hawaiian soils and various strategies to build soil of our own, for those of you with a big budget or no budget at all.


Related: In order to build good soil, you need good tools. My favorite tool to get this job done is the good old fashioned shovel. But make sure you buy one that’ll last, like this one from Amazon.

RADIUS GARDEN SHOVELOpens in a new tab.



Soil Types of Hawai’i

Similar to most tropical soils, Hawai’i is blessed with a rich volcanic loam.  Unfortunately, that rich Hawaiian soil is very thin in most places and completely degraded in others.  Years of neglect and abuse from the former sugar cane industry has left many of our soils depleted.

Much of Hawai’i Island is covered in recent lava flows that have very thin soils, most of it being pure rock.  This is a big challenge for those of us who want to grow food in this environment. We have to create our own soils.

In the areas around Hilo and to the north, there is a soil substrate known as Hilo soil.  It is the state soil of Hawai’i. It was once a rich soil, full of organic matter and micronutrients that allow plants to thrive.  The sugarcane industry knew this. They systematically plundered the soil for short term gains.

Similar soil to the Hilo soil can be found on the other islands, with slight variations.  Most soils on the islands have a thin crust of healthy, live soil with thick, heavy clay just beneath that thin layer.

Being that most of the available nutrients in the tropics are in the leaves and branches of the plants on the surface and not actually in the soil, it is up to us to replenish those nutrients as best as we can, constantly.

How to Build Soil in Hawai’i with NO Money

Like most things in life, there is more than one way to do something.  This is true with building soil. There are almost as many ways to build soil as there are gardeners, but a few basics hold true.

BUILD COMPOST

If you do not have any money, but have time and want to build the richest soil possible then you need to start composting.  A LOT!!

Build a compost pile to handle your food waste.  You should accomplish this in a variety of ways. The best way to build compost for the garden would be to build a worm composting system. There is a whole article that dives into it here.Opens in a new tab.

You should also build a compost pile.  I prefer the slow cook method of composting where you layer your green waste with dead leaves or other browns and just let it sit for a few months until it is ready.  If you are looking for speed, you can build a compost pile that you turn every couple of days to increase the cooking time of your pile.

Another great way to build compost is with chickens.  Create a fenced in area that is accessible to chickens but will contain the compost.  Build your pile and let the chickens have at it. They will scratch, they will poop, they will mix your pile for you.  You may just have to concentrate the material into a big pile from time to time, but this is a fantastic way to build quick compost with very little work.

SHEET MULCH

When I was starting my garden on my empty lot in Puna that had about an inch of soil and grass everywhere, I utilized an even simpler method to kick start my garden.  It was more labor intensive though.

We stockpiled a bale of cardboard and every piece of junk mail that we could find.  After identifying where the paths would be, we had the area where our garden beds would be.  We placed cardboard in our garden bed areas, along with our junk mail until you could no longer see the grass.  A couple layers of cardboard at least. This helps smother the weeds.

For the soil, I found a spot in Hilo that had a huge stockpile of sandy soil free for the taking.  Every time I went for a surf I would come home with a truckload of this soil. I would fill up my truck halfway with this soil and on my way home pick up some free horse manure that is freely available at the local stables.

This mix is what got me started.  I would cover the cardboard with it and proceed to plant after leaving it to sit for a month.  Initially, the soil was only good for growing daikon radishes and collards, but now it is rich enough through years of amending that I grow a variety of crops in it.

This wasn’t a quick option.  It probably took a year of filling my small pickup truck with way more soil than it should’ve been able to hold, but it cost me nothing except my time and energy.  Now I have soil that my neighbors are jealous of.

If you do not know of a giant free pile of soil, you can accomplish the same thing with cardboard, manure and free mulch from the dump.  Just make sure you let it all age for a bit.

Related: Can I Put Sawdust In A Worm Bin?Opens in a new tab.


Build Soil Right Away By Having It Delivered

Being that we are now in a post pandemic world, the desire to start our gardens is more pertinent than ever.  If you have a little budget, purchasing soil can be a great way to build soil for your garden FAST.

You can go to the store and purchase bags of soil.  If you have a small balcony garden or tiny backyard, this may be doable. But for others looking to build a larger garden, the cost of this option may be too high.

Instead, purchase your soil from a local quarry or landscape supplier.  Each island has its own version of a quarry where you can purchase material in bulk.  On Hawai’i Island in Puna we have Sanfords and Puna Rock. I prefer Puna rock. You can have the material delivered or you can pick it up yourself.  Call the quarry to help you determine how much you will need.

They have a couple of mixes that are decent but in no way the same as building your own compost at home.  You will have to enrich these soils. Look for cinder soil and mac nut compost.  

Those two items plus a load of manure mixed in with a little agricultural lime and you have yourself a garden that is ready to grow.  Over the years you will be able to enrich it to make it more healthy, but it will still be able to grow for you, but in a limited capacity.

I would like to add that many growers choose to use black cinder in their mixes as well.  It helps add drainage and micronutrients. This may be a better choice than cinder soil which has a red cinder mixed into it, which is not as good as black cinder. You can mix the black cinder with topsoil to make your own cinder soil mix. 

I have noticed over the years though that as the organic material breaks down it tends to leave an overwhelming amount of cinder in its wake.  Peat moss can be a good substitute for this problem, but the price of it can add up quickly.

Until the full spectrum of nutrients has been added to the soil, you may only be able to grow certain crops.  The best thing you could do to enrich it quickly would be to grow a cover crop that gets tilled in before you plant anything else.  This will ensure a healthy start for your soil and give you more success over the longer term.

Enrich Your Soil With Microbes

To enhance your soil even further, adding beneficial microbes to the soil can have a huge impact on how well your plants grow. You can accomplish this by creating a compost tea or through IMO’s.

To make a compost tea, I get some finished compost or worm castings, place some of it into an old sock or pantyhose and put it into a 5 gallon bucket with an aerator from a fish tank.  Let it sit for 24 hours and then spray it on my plants and soil within 2 hours.  

There are commercially available compost tea brewers that can be used for this purpose as well.

Another method to enhance microbes in the soil would be to create a pile of IMO’s, or Indigenous Micro-Organisms.  This is a technique laid out through Korean Natural Farming that harvests and replicates the natural microbes that already exist on your land.  These microbes do a fantastic job of increasing yields from poor soils.

Chop and Drop to Build Soil

Like I mentioned earlier, the bulk of the nutrients in the tropics are locked up in the organic matter of all of the plants, not the soil.  It is very important to get that organic matter to the soil where it can break down and leave its nutrients behind.

For perennials, that may just mean pruning branches and leaving the cuttings on the ground as a mulch. For your vegetable garden that may involve growing cover crops that get chopped and tilled into the soil.

This can also be accomplished through composting, but the chop and drop method is more geared to the lazy gardener like me.  Why duplicate the work of nature? I like to let nature do the work wherever possible.

Related: Hawai’i Food Forest: Feed Your Garden With Nitrogen Fixing Plants

Plant Perennials Instead of Annuals

Lastly, why even bother with all of this?  By importing soil we draw on resources that can be better used elsewhere.  Maybe your property just isn’t meant to grow annuals? Fruit trees can grow pretty well in our rocky and degraded soils with just a little mulch.

When you import soil, you run the risk of importing deadly pathogens and invasive critters onto your land.  Is it worth the risk?

I didn’t bother with it myself for almost two decades.  Now I am at the point where I would like to produce a little more of my favorite foods, so we are building a raised bed to grow those tasty annuals such as tomatoes, zucchini and peppers.

Whatever it is you choose to do, start growing food.  Don’t let the soil of the tropics stop you from doing otherwise.  

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Sean Jennings

Sean has been living simply Off-Grid in Hawai'i for over 18 years. He lives debt free on Hawai'i Island with his family and over 40 chickens. When he's not tinkering around the homestead, he's off exploring the shorelines for fish & surf.

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