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Nursery Media - Air in your mix...what's the big deal? — 01/29/2018View Details

Growers pay close attention to water and fertilizer. And we know that woody ornamental roots require a well-aerated growing mix - at least 20% free air space - to get enough oxygen to promote healthy growthand prevent disease. Yet, how often do growers neglect to seasonally monitor their mix for its porosity –its free air space after irrigation?

If you need to verify the porosity of your own mix, try this easy method. Keep detailed records for various crops, start to finish:

1. Choose several potted plants from a block to test. Tape over the pot drainage holes.

2. Carefully add water to each pot until you just begin to see it at the top of the container mix.

3. Without tilting the pot, remove the tape to catch the draining water for a minute or so.

4. Accurately determine the cc or ml volume of water using a small measuring cup.

5. Using the cm scale on your tape measure, determine your pot dimensions to calculate soil mix cc volume. Formula: πr 2 h (3.14 x average radius squared x mix height) for roughly cylindrical pots like a #1 or #3. For conical pots, the formula is the same, but divide result by 3.

6. Divide the collected cc’s of water by total soil cc volume. Multiply decimal result by 100 to get your percentage of unfilled pore space in the mix. (Air replaces all the water you collect.)

Consider how important AIR is to your potted woody profit experience…

What’s your test result? Most woodies grow best in a potting mix of 20-30% porosity. Root expansion and mix decomposition diminish free air space throughout the growing season, so a mix may test 27% to start, but by season’s end it may decline to 12-15%. If your mix tests below 22-24% from the get-go, consider using a more coarse mix, even if you just cautiously set up a significant side-by-side contrast trial. You’ll be glad you did.

Untrained crews may press down a mix too tightly at potting time. Stacking on a pallet after filling flats – it’s a poor handling practice if your potting mix gets compressed. Summer heat tends to subside after mid-late August. But unless trained otherwise, irrigation staff may complacently rely on irrigation timers instead of lifting pots and flats – using experienced judgment before cranking on the water.

How often do supervisors get riled up if a crew person lets a block of plants dry out too much, but if that same person over-irrigates, hardly anyone notices? In so doing, do supervisors effectively train irrigation crews to drown plants?

Watering crews have your checkbook in their hands. Over-watering containers - not

allowing them to dry down during the irrigation cycle - means a mix has less time with the minimum air needed to support vigorous, healthy roots. Phytopthora and other root infections may develop, getting progressively worse before they’re apparent.

These practices all foster inadequate soil mix porosity - conditions ripe for root disease and failure - literally at the finish line. What changes might you make in your operation if this provokes your concern? How may we help you with more information?

An excellent mix in our propagation experience is 75% coarse bark, no more than 10% coarse peat, and 15% perlite or pumice. You may wish to evaluate 90% coarse bark + 10% coarse peat. Baled bedding plant mixes, used for vegetable starts and plugs, are too expensive to use in large pots. But with thoughtful irrigation practice, as long as you incorporate slow-release fertilizer and include calcium, magnesium and micro-nutrients, even a pure bark container medium can grow healthy woody plants you’d be proud to offer.

At Heritage, we regularly evaluate our growing media for porosity, EC (soluble fertilizer level) and moisture. Simple methods - using a salt meter, lifting plug trays or pots to judge their moisture level – are easy but critical staff training elements. We closely monitor root development so we send you nothing but the most healthy, white-rooted woody liners at the end of the season.

We offer these ideas to help you profit with our plants, so they will grow up like healthy kids and make us all proud. It’s just a tangible, specific example of how Heritage is distinctively different. We aren’t just your supplier; we’re your growing partner.