Compost Guru Frank Gouin Answers all our Questions

Dr. Frank Gouin

Posted by Susan Harris
I’d heard Dr. Frank Gouin’s name mentioned almost reverentially for years and wasn’t about to miss his winter workshop at Homestead yesterday.    So without further ado, here’s what I learned.

About Gouin
Gouin is a pretty darn famous plant physiologist who taught and conducted research at the University of Maryland for 33 years until his retirement 14 years ago.  (He authored more than 700 published papers!)  He hasn’t stopped teaching, though, and Master Gardener classes are just one of the many venues for his lectures.   His chief accomplishments over the years include cloning the Wye Oak and developing a hot-sauce animal repellent, thermal blankets for container-grown winter ornamentals, and Osmocote 18-6-12.  That’s on top of his findings about composting, the subject he’s researched since 1972 and for which he’s best known.  He set up the compost system for Disney World, which now composts and reuses 80 percent of its waste, and many, many other clients.

Gouin, who lives in Deale, still grows Christmas trees, wreaths and swag for sale from his “Upakrik Farm”.   Catch his column in the Bay Weekly.

Compost Starter
This is important, and something we usually do wrong.  If you’re using a commercial compost starter (because your garden soil isn’t nutrient-rich) don’t let it sit in the bag, dry out, then just sprinkle it over your compost pile – that would be a “total waste”.  That starter has to be “activated” (who knew?)  Make a mud-like mix of soil or starter plus water plus 1 cup of sugar, stir well, let it sit for a day.   Then add 1/4 cup of a cheap dish detergent (for stickiness), stir again, and mix that into the compost.  For extra speed, add 2 cups of urea (nitrogen fertilizer) to the mud.  (To speed up the composting, definitely chop up your leaves first to increase their surface area.)

The Carbon/Nitrogen Proportion Needed for Compost to Happen
Another really, really important point is that compost happens best when the carbon-to-nitrogen ratio is 35-25 to 1.   Dry leaves alone have a ratio of 80 to 1, so that’s not enough N, but fresh grass clippings are perfect for providing the needed nitrogen.  Never, ever add sawdust, though – it’s SO high in carbon (400-800 to 1) it basically never breaks down.  If no grass clippings are available to add the required nitrogen (which is typical in late fall when we gather our leaves), use urea or blood meal.

The Moisture Needed for Compost to Happen
Dry leaves also simply don’t decompose into compost – without  water.  The mix should be about 50% water, in fact, and dry leaves are only about 3%.  Grass clippings,  however, are 80% water, so we see another reason that dead leaves and grass clippings compost together so well.  Gouin’s favorite tool for measuring the moisture of his compost bins?  His own bare hands!   He seemed to enjoy the squeamishness on the faces of his audience as he described reaching bare-handed into compost operations of all sorts – including chicken waste.

Composters and Bins
Small tumblers don’t have enough volume to stay hot and actively composting over the winter – only really large tumblers will do the job all year.  And don’t turn your compost more often than once a week because turning cools down the whole operation for a while.  And one bin or tumbler won’t do the job, either – because you need to stop adding fresh items and let the composting begin.  So Gouin uses and recommends a three-bin system.

Sign on Gouin's Truck

Benefits of Compost
Gouin applies 1-2 inches of compost as a mulch that provides a balanced diet of nutrients (something he refers to as “mineralization”).  Sadly, commercial farming operations typically apply just the big three nutrients – nitrogen, phosphorus and potassium (NPK) – but no trace elements, so yields decrease over time because they’re simply depleted.

Another amazing benefit of compost is disease suppression.  For example, where there’s black shank disease, amending soil with compost eliminates the disease problem.  Similarly, where root rot is a problem, amending the soil with 25-35% compost solves that problem and eliminates the need for fungicide – because compost contains not one but three naturally occuring fungicides.  He further explained that both beneficial and disease-causing microorganisms are killed in the process of decomposition, but only the beneficials come back after cooling.

What about Commercial Composts?
Their quality depends on the inputs, and vary quite a bit.  Just never apply more than 1 inch, then 1/2 inch the next year and thereafter.  The very popular Maryland Leafgro is very good, one of the best yard-debris compost products in the whole U.S. – just don’t overdo it.

Will Compost Inhibit Seed Germination?
He calls his an old spouse’s tale (a term Gouin prefers to the sexist term “old wives tale”).   He uses compost in seed germination mixes (with peat) all the time, and the seeds germinate just fine.

About Peat
Gouin’s preferred potting soil is 2/3 compost and 1/3 peat.  Asked about the dire warnings about peat being harvested unsustainably, he agrees that that used to be the practice, but no more.  At least the Canadian peat supplies that make it to our stores are now harvested sustainably – they remove just 6-10 inches, then allow the peat bog to restore itself for the next 20 years.

Kitchen Scraps
Can they be added to the compost operation?  Absolutely, as long as they’re buried deep inside.  “No rat’s going to burrow into 180-degree compost.”   Kitchen scraps are heavy in nitrogen and if you have no dead leaves to provide the needed carbon, just add some shredded newspaper or cardboard to the mix. (Though not too much cardboard, which is loaded with boron – and sorry I didn’t catch why that’s bad).)

“Horse manure is terrible” – it’s full of weeds.  Turns out horses don’t have an efficient digestive system.   Then when sawdust is added, as it often is naturally in the stable, that just makes it worse.  (Straw would be far better as stable bedding).  Chicken, cow and pig manure are just fine, though – their digestive systems are more efficient.  Again, make sure it’s not mixed with sawdust.

About pH
Asked if oak leaves produce acidic compost, Gouin says not to worry, that composted oak leaves have the same pH as any other leaves.  But here’s what I found most enlightening about compost and pH: that even acid-soil-loving azaleas grow well in ph-neutral soil if the organic matter content is high enough.  So if you add compost regularly and increase your soil’s organic matter content to 5 percent or so, then the actual pH level just doesn’t matter!

Wood Chip Mulch
We’re hearing that wood chips are terrible mulches because they draw nutrients out of the soil (they’re needed to break down all that carbon in the wood chips) and Gouin says this is true.  Hardwood mulches also create a manganese residue, which again is a problem.   Pine bark mulch, being a softwood, is fine – though Gouin says that mislabeling can and does occur.

This is interesting – Gouin told us that worm castings (the product of worm composting) aren’t as valuable as conventional compost because it doesn’t have the high lignin content found in, for example, dead leaves.

Compost Tea
There’s all sorts of controversy in the gardening world about the value of aerated compost tea, so naturally I asked Gouin to weigh in.  He echoes many academics in their assessment that while it provides nutrients, “It’s very hard to find research that supports compost tea” as a disaese suppressant.  And even for its nutrient-providing benefits, Gouin thinks that regular compost is better.  If you do use compost tea, make sure to keep it aerated.

More Big Tips

  • Buy a compost thermometer.
  • Don’t cover your compost bins and piles.  If it’s raining a lot, just shape the pile like a teepee to let the rain run off.  During dry periods, flatten the pile so that water is retained.
  • Coffee grounds compost well.
  • Black walnut leaves can be composted – no problem.
  • Fireplace ashes should never be added to compost piles – their pH is too high.
  • Should bins be in sun or shade?  It doesn’t matter.
  • If you do composting wrong, your neighbors will know it – by the smell test.  Insufficient oxygen is the biggest problem with people’s compost systems, and it causes the whole pile to stink.  Too much nitrogen?  Also, the stink.  Too much water?  Stinky.  “The smell is enough to gag a maggot.”

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