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| Photo Credit: Tammy Clayton |
| This rose plant is very yellow, with the newest leaves definitely pointing toward a lack of iron in the potting mix. The problem can be fixed with an application of bonemeal or chelated iron. |
No matter what shade your green thumb, chances are you’ve got (or once had) at least one plant in a container, most likely potted up in some blend of store-bought potting soil or mix. This soilless media was designed to grow plants in an unnatural environment. After all, plants grown in plastic containers in regular soil are prone to many problems, since plastic pots don’t allow air to flow through. Plus the few small holes at the bottom just aren’t adequate drainage for real soil. So professional growers and home gardeners have turned to natural, soilless blends to assist in getting air to root systems and create quick drainage. (Both are necessary to succeed in growing plants in containers.)
No matter what brand of potting mix you buy, it’s sure to contain varying portions of fine pine bark, perlite or vermiculite and perhaps a pinch of topsoil. But the common main ingredient among the different brands is sphagnum peat moss. Sphagnum is naturally very acidic, with a pH of 3.5-4.5. (High acidity means the same as low pH.) Overall, soilless media have very low pH levels. While manufacturers blend in dolomitic lime to help raise the pH, there can still be problems when trying to grow plants that don’t like acidic soil. | Add Photo to Journal |  | | Photo Credit: Tammy Clayton | | This Loropetalum is either suffering from not enough water or the potting mix has too high of a pH level (alkaline). |
It’s also hard to get a good bead on the pH within the mix of the medium, so it’s typically stated as a pH range like 3.5-7.5. (Most likely this is from the loose, fluffy sphagnum versus the weighty chunks of limestone.) And some parts of the bag can be less acidic than others as the lime shifts around during shipment.
While many plants adapt to lower pH levels, others turn a sickly yellowish green and begin declining. And yes, some will die quite rapidly. But luckily you can do something about this unfortunate situation. If you know what pH your plants prefer, you can amend your potting soil before you plant. Sometimes adding more lime is fine, but other plants might do better with a little topsoil added into the mix. | Add Photo to Journal |  | | Photo Credit: Tammy Clayton | | The yellow leaves on these Japanese cleyera show signs of drought and a lack of available nitrogen in the potting mix. |
In my own small nursery, I potted plants up with my own mix of 50 percent topsoil and 50 percent Michigan peat with a regular soilless mix and vermiculite. Incidentally, plants I brought in from another grower required far more watering than those I potted myself. The plants also had a different leaf color (mine were a deeper green, while the plants I brought in had a yellow tinge to the leaves). Customers swore they were buying two different plants when they bought one growing in my mix and one from another grower. But after a few weeks in the ground, that difference in foliage color disappeared.
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| Facts |
- Whether you plant something in the ground or in a container, knowing the range of pH level that each plant does well in is important to gardening success. pH is measured on a scale of 1-14, with 7.0 being neutral. Anything lower than that is acidic, and anything above is alkaline.
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| Tips |
- No matter what kind of plant you want to grow in a container – tree, shrub, vine, perennial or annual – be sure to keep a constant eye on its health. Some plants will do absolutely fine in a one-size-fits-all potting mix – but other plants have specific needs not met by regular blends. If plant health declines, the problem may be in the mix.
- Michigan peat is completely different than sphagnum peat moss and peat moss. Michigan peat contains a lot of moist humus and rich black soil. If you find a source for Michigan peat, by all means indulge in a bag or two. Then mix 50 percent topsoil and 50 percent Michigan peat, and you’ll have the “perfect” garden soil with very little acidity.
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| Faqs |
- Q: Are sphagnum peat moss and peat moss the same thing?
A: No. Some potting soils use silty peat moss and not sphagnum moss. Colorado State University tested many retail brands of potting soils and found the results of mixes with plain peat moss rated poorly. So always check the label. - Q: What kind of planter is better: plastic or terra-cotta?
A: Plastic containers don’t breathe, so plants will grow slower in them than in terra-cotta. Try this experiment: Take two identical plants, pot one in clay and one in plastic, then grow them next to each other. Care for them the same, and in about a month compare them. While the potting mix in the clay pot will dry out faster than the plastic pot, the roots of the plant in the clay container will grow more rapidly as they reach for the air at the sides of the pot. And remember: Healthier roots make for healthier plants!
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