Monday, June 1, 2015

Mystery of the Disappearing Mulch

I've  heard plenty of new gardeners complain bitterly that the mulch they use simply disappears. Poof. Most of them believe that it melts or dissolves into the ground, disappearing between the lava rocks. I've heard people say that they put down weed cloth over the lava rock before making their lasagna gardens because they don't want their organic material to wash down between the rocks and disappear. Other gardeners will say that buying or hauling in mulch material isn't worth it because it just disappears. Aaaaahhh, the mystery of the disappearing mulch! Where's Sherlock Holmes when we need him!

Whenever a gardener complains to me about disappearing mulch or compost, apparently hoping for advice or sympathy, I respond , "Of course. I want my mulch to disappear!" 

Mulch and compost seems to disappear because it is decomposing and being consumed by soil life, thus being converted into something that my plants can use as fertilizer. So if it doesn't disappear through the seasons, I'd be worried that my soil was "dead". And if the mulch/compost doesn't degrade, then my plants and garden worms aren't getting fed. So I say, rot baby rot! 

Here in the tropics the mulch and compost seems to decompose fast. Where my homestead is located, the temperature is constantly moderate and we get a decent amount of rain. So conditions are ideal for the soil microbes and the worms. Add to these facts that I don't get cold winters, my organic material gets the opportunity to decompose 12 months a year. The process never stops. When I gardened in NJ, the growing season was much, much shorter. So mulch lasted "the season".....which actually was only 3 months for most crops. That's no different than how long I expect my mulch to last here. It's just that in New Jersey mulch only needed to be applied once, sometimes twice during the year. Here in Hawaii where I can garden year around, it needs to be applied at least four times a year. It just seems to be more than usual, but it's not. 

I rake or till a bit of compost into the soil between each crop. Some of the old mulch also gets worked in. Then I apply fresh mulch. This cycle repeats itself with each crop. Thus each new crop is being fed by the decomposing mulch from crops before them. 

So rather than bemoan disappearing mulch, rejoice that the system is working. I do. I'm glad to see my mulch decomposing. It means that I never need to buy expensive store bought fertilizer. 


  1. Your posts about ash and mulch got me thinking. What kind of soil do you mostly find in HA? Back in Iowa we had glaciated soil. Deep loam full of minerals and organic matter. Perfection (where they didn't let it erode down to the Gulf of Mexico). Of the 3 main kinds of soil seems like Hawaii soil wouldn't be heavy clay or sandy. Seems like it might be a kind of loam with high organic matter. I've never got the shovel out and dug down.

    1. Soil type varies greatly from island to island. On Big Island, there are several regions of different soil types. I'm not much into all the soil science, so I don't recall the names. But all Hawaiuan soil is made up from volcanic derived material (lava, ash, pumice, lava sand, pele's hair, cinder) and degraded organic material. The soils here are young, thus no sandstone, limestone, glacial deposits, etc.

      On my homestead I have soils that are hydrophobic and other areas that are the opposite. But most spots are layers of degraded, fine particle organic material located between lava chunks and boulders, or atop pahoehoe or blue rock. It has been challenging to get this soil to grow vegetables well. Only with the addition of lots of compost, mulch, manures, cinder, and sand have I been able to create successful gardens.

      My soil at the seed farm only five miles away is completely different. It is a fine powdery, hydrophobic dust amid a lot, lot of lava rubble. I'd say 95% lava. While grass and Christmasberry trees thrive, just about anything else struggles. It is taking quite a bit of effort and material to upgrade this soil into something that will grow vegetables.

      The comment about the shovel brought a smile to my face. In Ka'u, a shovel isn't the tool of choice. One is better off with a pick or O'o bar. Too many lava chunks for using a shovel. my gardens I can use a shovel. That's only because for years I've been removing the rocks.

  2. Thanks for your reply. I had never heard of hydrophobic soil. I would have said immediately that we have hydrophobic soil but we don't. It just seems that way. When it gets really dry here you can fill a hole with water and the water will not seep down. It just stays there like it's in a clay bowl until it evaporates. But It's not true hydrophobic. Hoo boy, seems like everywhere I go or want to go there are major soil challenges. My husband wanted to make sure that if this plan to move to Hawaii works out that we find a place that has soil. His reasoning was so we could make a horse arena and also have pasture. Now I see that there's another reason if I want a small garden. I remember the Miranda's saying they fed hay to their horses because the pasture grasses were so full of moisture as to not be nutritious. Isn't that the oddest thing? Here you have this paradisical environment that turns out to have major challenges to growing things. A place where tropical plants get so big that one is tempted to say "Honey I shrunk the adults!". (I felt that way in the botanical preserve by Hilo.)

    Is an O'o bar something to chip lava with? Is that related to A'a? I love Hawaiian.