Pick a Horticulturist’s Brain Today


by Susan – Part 2 of my interview with Mitch Baker of American Plant Food.
Here I was talking to an
actual horticulturist, one who taught the soils section for my DC
Master Gardener class (and was terrific!), one who’s doing videos for
MonkeySee.com (coming this month), why not pick his brain?  My thinking

  • What’s he think of our topsoil debate?  Bagged topsoil is, at best, a composted blend or river bottom silt. Look for
    something that’s at least fully composted.  He urges people to spend more for a really good product, like Bumper Crop or
  • How long can we go without watering our lawns before they DIE?  Six weeks for most species.
  • How do does treat his own lawn?  Around Labor Day he applies an
    organic fertilizer like Ringer or Bradford, overseeds with a turf-type
    tall fescue, and applies calcium.  He applies nothing in spring.
  • What about applying compost instead of fertilizer?  It only
    supplies about half the 2 pounds of nitrogen per 1000 sq needed by
  • Other lawn products he recommends are Safer Lawn fertilizer (8-1-1,
    with micro-organisms), which can even be used in the summer; Safer
    Grass Stimulator, which is kelp and does not include the
    micro-organisms; and compost tea, another product that’s slow-acting
    enough to be used when it’s hot.
  • What fertilizers does he recommend for the garden?  For perennials and woodies, an organic
    fertilizer in the late fall, so they’ll be ready to do their thing the
    following spring.  That provides the  actual
    nutrients.  Then for the "biology," the microorganisms, use compost tea.  Conversely, if you use leafmold mulch (as I do) in
    combination with compost tea, that’ll do the trick.
  • Why all the disagreement about which mulches are best, which harm
    plants, etc.?  Mitch says it’s because of overapplication of mulch, which we’re seeing
    now more than ever, up to 10 inches, plus those damn mulch volcanoes. 
    He recommends 1 1/2 to 2 inches, max!  At that modest amount, he
    says that all mulches will do the job (weed suppression, temperature
    moderation, etc).  Even bark will break down if it’s applied thinly
    (less than 2 inches) and if the biology is there (cue the compost
    tea).  Even the dreaded iron oxide used in those butt-ugly colored
    mulches are no problem when the mulching is a thin layer.  And our worries about magnesium leaching from shredded hardwoods?  Again it’s no problem
    if the mulch is applied thinly.  The only exception is wood chips – they really do tie up nitrogen and pull it from the soil.  So unless
    it’s composted first, use it only on paths and play areas, not around
    plants.  Okay, roger that.

My take-home message from chatting with Mitch – why not try an organic fert in the garden
this fall?  Maybe my poorer-performing plants will finally perk up.  My laissez-faire attitude may fit my
hippie-dippie personality but is doing nothing really the best practice?  Results will be reported right here on the Rant.


  1. Mitch’s advice is regional, for sure.

    In my own experience here in the Pacific Northwest, lawns can go dormant in summer, and green right back up once the rains begin. No supplemental watering needed if you don’t mind the tawny lawn look during summer.

    In addition, I’ve noticed that leaving the grass clippings on the ground instead of bagging them up keeps all of that nitrogen where it’s needed and saves me work by not having to dump bagged clippings and not having to go back over the same area with a fertilizer spreader.

    Regarding the often stated warning about wood chip mulches pulling nitrogen from the soil: my understanding is that this has been proven false. Yes, the top 1/2 inch of soil in immediate contact with wood chips does contain less nitrogen than the deeper soil, but to suggest that nitrogen is being pulled up through the deeper layers of soil to satisfy the needs of wood decaying microbes on the top paints a scenario that defies the laws of physics, not to mention microbiology. We generally mulch around trees, shrubs and perennials to keep weeds down, but these plants generally have pretty deep root systems, and I rarely see evidence of nitrogen deficiency in mulched landscapes. In addition, if nitrogen were being pulled up through the soil profile by some unknown force, it wouldn’t matter how deep the wood chip mulch was, since an umlimited supply of nitrogen would cause that mulch to all break down at the same rate, wouldn’t it? Instead, 2 inches of coarse mulch takes a few years to break down to the point where it needs to be replenished. Maybe in the sandy soils of the Chesapeake Bay area, there’s more nitrogen movement, but in clay soils it tends to stay put. The warning about wood chips and nitrogen seems like one of those notions that gets repeated over and over in gardening and landscaping literature without checking for accuracy.

  2. Right on, Ellen, regarding your comments about both grass clippings and wood chip mulch!

    Also, as per my article, “Improve your soil by raking less,” in the current (October 2007) issue of Fine Gardening magazine, research at Michigan State, Purdue and Cornell conducted more than ten years ago has shown that mowing, quite literally, feet of tree leaves into lawns each autumn not only doesn’t hurt turf if done correctly, but can actually improve it over time!

    Plus, keeping autumn leaves on our property reduces municipal fuel consumption, thus improving the environment and slowing the rate of local tax increases!

  3. Question concerning compost tea: If the microbial life in compost tea is aquatic, how does it survive in a non-aquatic environment, i.e. soil application, in order to benefit the soil ecology?

  4. In response to Daniel’s comment: A number of microorganisms that you find in aquatic environments are able to survive in soils. Soils are not dry ecosystems – and each soil type has it’s own characteristic ‘water-holding capacity’ where water is retain between the different minerals components of soil (sand, silt & clay) – so almost always some water is available as microhabitats in soil where microorganisms that prefer more aquatic environments can thrive. Water enters soil via capillary action (from the water table) and as rainfall – so while your soil often appears ‘dry’ – there is almost always a measurable amount of moisture present (and remember that microbes are small). With that said, rarely does the introduction of microorganisms to soil result in a more beneficial microbial community – perhaps in the short term, but rarely in the long term. Also, it is misleading to think that the organics used to promote microbial growth in compost teas just benefits beneficial microorganisms – those pathogens such as Pseudomonas sp and Burkholderia sp. love those organics as much as anybody (aka any microbe) – and if anything, those teas benefit the more fast-growing, opportunistic microoganisms that can take advantage of the readily available carbon source (it’s all in the kinetics!). If you want a diverse and plentiful soil for your gardens – the best thing to do is to support the microbial community that has already adapted to that particular soil type and environment by enriching the soil with degradable materials – nothing beats leaves and grass clippings that come right from your own lawn.

    (Okay, for all you out there screaming RHIZOBIUM – those are high concentrations of one microorganisms that forms a species-specific relationship with plants in the vicinity – the percentage of the inoculum that actual connects with a legume root to form a nodule is really, really low. It’s an overkill kinda thing – and the Rhizobium numbers don’t increase considerably in the native soils over time.)

    Hmmm. This was a geeky moment.

  5. Now that’s what I’m talking about!

    The real world is geeky – we just need to figure out a way to explain it clearly and make it applicable to the stuff we see and do every day in our lawns, landscapes and gardens!

    Sharing the “hippie-dippie” stuff is fun, but I want to encourage the Garden Rant ladies to continue pursuing the fascinating geeky stuff and delivering it in a way that’s clear, understandable and applicable.

    You have a very powerful voice, ladies, and I look forward to watching it evolve!

    Great stuff, Pam!

Comments are closed.