Perfect container mix every time, what could possibly go wrong?

Over the years, you no doubt have (or will) perfect your own secret recipe for the perfect container mix to suit your needs. In with the pine bark goes a careful blend of sand, compost, or peat moss etc.

And, over the years, you’ve probably had a few dud mixes or unexpected poor growth or plant loss. What happened? Did the pine bark over-age, or another ingredient change somehow? When did it happen? A dud batch today may have been caused by slow, unperceivable processes gone unnoticed months ago.

Fines can be expensive for the over-aged…

Old supplies risk over-aging which increase the amount of ‘fines’. Pine fines pack closer together due to their small particle size, making a tighter substrate with less airspace. This higher density has a double impact on cost:

  1. More substrate is needed to fill a container
  2. A given volume is heavier to ship

Less airspace means poorer drainage and leads to a wetter substrate. Even if plants can tolerate this, it increases the risk of water-logging and requires careful management of watering.

Don’t forget to wet and turn

Not moistening components before mixing decreases aeration. For example, mixing dry sphagnum peat moss and dry pine bark leads to low porosity and poor moisture retention. The moss isn’t spongy and can’t keep the pine bark structure well separated.

Even aged and stabilized composts dry-out when stored undisturbed, requiring moistening every few weeks, especially if they heat-up.

Regular turning of inventory is important. Dry bands and anaerobic pockets will form in undisturbed mixes, and temperatures will climb. Also, the less stable the mix, the more frequently it will need turning (possibly every day) and it will need turning until it no longer heats beyond 140ºF. Windrows that are too tall (over 10’) make inventories difficult to turn and increases the risk of damaging temperature spikes.

Pine-fresh headaches

Unstabilized green/ fresh pine bark catalyzes rapid decomposition and heat/ moisture loss in stored container mixes. This greatly increases the chances of anaerobic conditions and requires for careful aeration and water management. Temperature spikes even char bark particles, unpredictably altering their physical and chemical properties.

Aged pine is much more stable, but poor management of the aging process will create an inferior mix containing anaerobic pockets.

Anaerobic workout

Moisture, temperature, and oxygen must be carefully managed in substrate inventories to prevent anaerobic conditions. These conditions usually lead to acidic conditions (pH<3.8) and high electrical conductivity (EC >1mScm-1) that damages/ kills nursery crops.

In un-turned inventory, dry bands, gray with mycelium, appear 2-3’ from the top of the pile. This impervious layer starves beneficial aerobic microbes of oxygen and creates anaerobic conditions.

Anaerobic microbes generate acetic acid and, with moisture, extract many salts including potassium. This leads to pockets of low pH, high EC, and high potassium concentrations. This kills or stunts the growth of plants.

KYM – Know Your Mix

It’s hard to measure the quality of each component and it’s effect on a complex mix. The best strategy is to have the Low Air Filled Porosity (AFP), pH and Electrical Conductivity (EC) of the completed mix tested on delivery. Before the damage is done.

Insist on scientifically-proven quality controlled container mix. WE DO.