Gardeners ask master gardener Paul James about reusing potting soil, the best time to water container plants, and more.
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Master gardener Paul James fields questions from gardeners:
Q: Paul, like you, I grow all kinds of plants in containers. Can I reuse the potting mix?
A: Absolutely. After all, potting mix is recyclable, and it would be a waste to throw it away. I replace about one-third of the mix each year. Simply dig one-third of the potting mix out of the container with your hands or a trowel. Add an equal amount of fresh potting mix or compost, and blend the mixes together. Actually, I only do this when I have a container or two to plant.
When I have a lot of potting to do, I dump all the potting mix from my containers into a wheelbarrow. Then I add fresh potting mix or compost equal to about one-third of the total, and refill my containers. Of course, I do this in batches since I now have around 144 pots to fill.
If any of your plants suffered from diseases of any kind during the previous growing season, you might want to sterilize the potting mix before you replenish it. And to do that, the first thing to do is moisten the soil thoroughly. Slowly pour boiling water over the old potting mix. Let the water drain, and add another round of boiling water.
If you live in an area where winter temperatures stay below freezing, say from Zone 4 and northward, you may want to remove the potting soil from your clay pots before winter sets in. Otherwise, you may find that your pots look like. You may also want to consider buying double-fired pots. They're a little expensive, but they can be left outdoors during the winter even with potting mix in them.
You can also recycle old potting mix by dumping it in a compost pile. During the following spring, mix up a batch of potting mix by combining two-thirds store-bought potting mix with one-third homemade compost.
Q: Is there such a thing as a best time to water container plants?
A: Well, some people think so, and my own experience confirms the latest research on the subject. Years ago, I watered my container plants early in the morning, just as I do my landscape plants. But a few years ago, for reasons I don't even remember, I decided to switch to watering my container plants in the afternoon. In no time at all, I noticed an incredible difference in the overall health of my plants, and recently, two university researchers published results on the same thing. They narrowed the best time to water container plants to between 3:00 pm and 6:00 pm. Incredibly, their results showed a 60 to 70 percent increase in plant growth. Apparently when container plants are watered early in the day, they experience water stress by midday. And water stress has a cumulative effect on the health of plants.
Q: Which plants can survive in containers outdoors year-round?
A: It depends on where you live and the plants in question. From Zone 5 and northward, only the hardiest perennials are likely to survive in containers left unprotected outdoors during the winter months. And while the plants may survive, chances are the pots may not. From Zone 5 and southward, a good many plants will do just fine, and likewise, the farther south you go, the longer the plant list gets. Determining which plants will survive the winter outdoors is largely a matter of trial and error. So my suggestion is, if you're not sure, remove the plant from its container in the fall, and plant it directly in the garden.
Q: Where in the world do you store all your containers?
A: I store them all over the place, including the barn, the garage, along a wall of the house and just about anywhere I can find room. But while dealing with that very dilemma just last fall, I had a brainstorm. I decided to stack them in a random sort of artsy way along a wall next to my patio, and I must say that I think it looks pretty cool. Of course, they won't stay there for long because I'm preparing to fill them all up with plants.
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