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This column is for those who purchase flowers for their boxes and pots with all the optimism held within a sunny spring day, only to feel like you’re doing them dirt by planting into soil used the previous year. Recycle potting soil? What, are you dirt cheap?
Personally, I think you’ve reached higher ground.
As a practical matter, my experiences have been good re-using soil — with a hedge. Well, four of them actually.
— The plants grown in the pot the previous season were healthy.
— The biggest part of this season’s plants having been removed prior to over-wintering.
— The soil dries out over the winter.
— You plant next spring with healthy plants.
In a greenhouse the running joke is that a commercial growing mix, sometimes called a sterile mix, is soil until it hits the floor, whereupon it becomes dirt, is treated like dirt and carted off in a dumpster or manure spreader. Obviously greenhouse growers do this because the size of their profit depends upon every little plant unit going to market healthy.
So, wouldn’t you know it, every greenhouse is a breeding ground for plant disease. No wind. No rain. No winter storms to stop disease. Oh baby, a hothouse, unfortunately, doubles as an incubator for plant scourges like fungi, bacteria and insects, which spread viruses. Consequently, growers go to great lengths to prevent disease, and dumping floor sweepings is one of the cheapest places to start.
Your flower pots at home are a different matter. There are plenty of natural disease controls stopping plant problems before they truly take off — a dry climate, wind, rain and winter being among them.
Healthy plants given a favorable environment will resist most diseases — just as you and I resist most diseases if we’re not weakened. That’s the money statement.
Which brings me to what can go wrong if you reuse soil.
Peat moss, a growing plant prior to being harvested, is actually pretty sterile stuff. Sphagnum peat, the type of moss most often used, grows in bogs and creates and exists in an environment that is more acidic than most plants and many bacteria can tolerate, so weeds and disease are reduced as problems for growers.
Like good paper towels, peat holds more than its weight in water and yet, when the excess water drains away, there is plenty of air in the soil for roots to thrive in. It is truly an almost perfect medium for growing little plants.
This gets even more arcane. Long fiber peat is better than short. Golden is better than black. Block cut is better than sucked up with a vacuum mounted on a tractor.
Of course, vacuumed-up, short-fibered black peat is cheapest and easy to find.
Peat fiber dynamics are important to plant geeks like me. One fascinating aspect is that peat moss behaves like a woolen sweater. It shrinks when it dries out. It simply won’t regain its original size once it’s shrunk. Shrink and swell daily and the fibers break into smaller fibers becoming finer and finer.
The fines clog up the open spaces in the soil. Air is as important to roots as water. Re-used peat over time becomes muck. Muck and air do not share the same spaces. Mixing in some fresh peat, say 25 to 35 percent each year, will add some life to your potting soil. Put the old peat in the bottom of deeper pots. In standard-size plastic window-boxes, which are really too small for growing plants through summer, mix it up well. Throw in an extra new handful or two.
Make sure it’s new. Not the stuff that over-wintered at your local peat center. That soil works well as filler, but only slightly better than the peat already in your pots. That’s because the pH in stored soil mix rises over time, particularly if it is wet.
I’m assuming that we all know that pH is to acid or alkaline as edible is to hot or cold. For example, when it comes to plants, pH pretty much determines what’s edible for dinner. A too high pH (alkaline) and plants don’t get enough iron, even if it is in the soil. A too low pH (acid) and the manganese and iron balance gets out of whack and can get a little toxic, leaving a yellow herringbone pattern stamped across your geranium leaves.
Commercial soils contain calcium as a way of raising the pH of the naturally acidic components in soil mixes. The calcium does a number of useful things. It is a way of providing calcium to growing plants, prevents wild swings in pH (buffering capacity) and moderates the uptake of nutrients (balanced cation exchange capacity).
However, in moist stored soil the calcium continues to break down, dissolve, freeing more of the calcium and its pH raising properties to the soil mix. Most annual flowers, with a few exceptions, grow best in a soil with a pH of 5.8 to 6.2. I have seen stored soils attain a pH of 7.8, which grows a pretty yellow plant.
You can lower the pH of your soil simply by fertilizing more often with an acidifying blend like 20-20-20 fertilizer — the most common blend used in over-the-counter fertilizers. How often is more often? Three times a week would not be too frequent. Most commercial growers fertilize pots and baskets two days in a row then go one day without, and so and so on. Some growers, in an effort to manage alkaline water, feed constantly with a reduced rate. From what I’ve seen, the average homeowner or business should feed more often, if they want their flowers to reach full potential. Controlling soil pH is one of the reasons to fertilize.
After all that folderol about soil, here is the overriding reason to re-use soil: If you plan to spend only so much per spring on your gardens, flowers come in more colors than peat.
Personally, I think you’ve reached higher ground.
As a practical matter, my experiences have been good re-using soil — with a hedge. Well, four of them actually.
— The plants grown in the pot the previous season were healthy.
— The biggest part of this season’s plants having been removed prior to over-wintering.
— The soil dries out over the winter.
— You plant next spring with healthy plants.
In a greenhouse the running joke is that a commercial growing mix, sometimes called a sterile mix, is soil until it hits the floor, whereupon it becomes dirt, is treated like dirt and carted off in a dumpster or manure spreader. Obviously greenhouse growers do this because the size of their profit depends upon every little plant unit going to market healthy.
So, wouldn’t you know it, every greenhouse is a breeding ground for plant disease. No wind. No rain. No winter storms to stop disease. Oh baby, a hothouse, unfortunately, doubles as an incubator for plant scourges like fungi, bacteria and insects, which spread viruses. Consequently, growers go to great lengths to prevent disease, and dumping floor sweepings is one of the cheapest places to start.
Your flower pots at home are a different matter. There are plenty of natural disease controls stopping plant problems before they truly take off — a dry climate, wind, rain and winter being among them.
Healthy plants given a favorable environment will resist most diseases — just as you and I resist most diseases if we’re not weakened. That’s the money statement.
Which brings me to what can go wrong if you reuse soil.
Peat moss, a growing plant prior to being harvested, is actually pretty sterile stuff. Sphagnum peat, the type of moss most often used, grows in bogs and creates and exists in an environment that is more acidic than most plants and many bacteria can tolerate, so weeds and disease are reduced as problems for growers.
Like good paper towels, peat holds more than its weight in water and yet, when the excess water drains away, there is plenty of air in the soil for roots to thrive in. It is truly an almost perfect medium for growing little plants.
This gets even more arcane. Long fiber peat is better than short. Golden is better than black. Block cut is better than sucked up with a vacuum mounted on a tractor.
Of course, vacuumed-up, short-fibered black peat is cheapest and easy to find.
Peat fiber dynamics are important to plant geeks like me. One fascinating aspect is that peat moss behaves like a woolen sweater. It shrinks when it dries out. It simply won’t regain its original size once it’s shrunk. Shrink and swell daily and the fibers break into smaller fibers becoming finer and finer.
The fines clog up the open spaces in the soil. Air is as important to roots as water. Re-used peat over time becomes muck. Muck and air do not share the same spaces. Mixing in some fresh peat, say 25 to 35 percent each year, will add some life to your potting soil. Put the old peat in the bottom of deeper pots. In standard-size plastic window-boxes, which are really too small for growing plants through summer, mix it up well. Throw in an extra new handful or two.
Make sure it’s new. Not the stuff that over-wintered at your local peat center. That soil works well as filler, but only slightly better than the peat already in your pots. That’s because the pH in stored soil mix rises over time, particularly if it is wet.
I’m assuming that we all know that pH is to acid or alkaline as edible is to hot or cold. For example, when it comes to plants, pH pretty much determines what’s edible for dinner. A too high pH (alkaline) and plants don’t get enough iron, even if it is in the soil. A too low pH (acid) and the manganese and iron balance gets out of whack and can get a little toxic, leaving a yellow herringbone pattern stamped across your geranium leaves.
Commercial soils contain calcium as a way of raising the pH of the naturally acidic components in soil mixes. The calcium does a number of useful things. It is a way of providing calcium to growing plants, prevents wild swings in pH (buffering capacity) and moderates the uptake of nutrients (balanced cation exchange capacity).
However, in moist stored soil the calcium continues to break down, dissolve, freeing more of the calcium and its pH raising properties to the soil mix. Most annual flowers, with a few exceptions, grow best in a soil with a pH of 5.8 to 6.2. I have seen stored soils attain a pH of 7.8, which grows a pretty yellow plant.
You can lower the pH of your soil simply by fertilizing more often with an acidifying blend like 20-20-20 fertilizer — the most common blend used in over-the-counter fertilizers. How often is more often? Three times a week would not be too frequent. Most commercial growers fertilize pots and baskets two days in a row then go one day without, and so and so on. Some growers, in an effort to manage alkaline water, feed constantly with a reduced rate. From what I’ve seen, the average homeowner or business should feed more often, if they want their flowers to reach full potential. Controlling soil pH is one of the reasons to fertilize.
After all that folderol about soil, here is the overriding reason to re-use soil: If you plan to spend only so much per spring on your gardens, flowers come in more colors than peat.
