Q: Is it OK to reuse potting soil to repot a plant? (e-mail reference)

A: The answer is no! Always use fresh, pasteurized media for repotting. Use a new pot or one that has been thoroughly cleaned!

Q: I used to have good luck growing pansies in a pot, but for the past four years they have started turning yellow and the buds have dried up. I don’t see any aphids on them. I have sprayed, which hasn’t helped. I noticed a friend’s pansies were also turning yellow. What can be wrong and what can I do in future years to prevent this? (Fargo, N.D.)

A: Perhaps you are expecting too much from them. They do best in the cool weather of spring and fall. Recent hot weather, especially when the plants are grown in containers, could be the cause of their decline. Otherwise, I suggest going for enriching the soil with sphagnum peat moss. Our plantings in Williston and Dickinson still look good at least in part because of that treatment.

A: I don't know about the fish/plant combo, but paper white narcissi and amaryllis make good bulbs for such planters. Generally, a "rock garden" is established just for physical support, but if you had another means of doing that, that would be acceptable as well. My concern is for the fish. How would the oxygen that it needs get into the water?

A: Experts will tell you what they experience under their conditions, which are often not very well explained. Generally, you should know the approximate volume of the container the plant is growing in put approximately that amount of water in each time you water. This will, of course, result in the water coming out of the bottom of the container since it is filled with soil. But like you, I find this is fine for a small container but a headache for a larger one, so I don't do it, choosing instead to water a couple of times a week (when I think of it) with the same amount of water each time, about half a gallon. And, believe it or not, the plant does beautifully for me under this treatment. So, my "expert" advice? Go back to what you were doing before all the experts confused the issue. The fungus you're seeing growing is a saprophyte, not a parasite, and will not harm your plant. Simply scrape it off or repot.

Q: Can you please answer the following questions; my husband and I are not agreeing.

Question No. 1: If I replant a baby houseplant (from a 1-inch pot) in a too-large pot, will it die? Is there a very slight chance--let's say 10 percent maybe--that it will not die but live and not grow much, or not at all?

Question No. 2: Can a plant go into shock and die if it's moved to a different house, a different state or even to a different room in the same house? (e-mail)

A: I'll be glad to settle marital difficulties such as this. Here are the answers to your questions:

No. 1: No, not very likely.

No. 2: Yes, very likely.

Now, for some explanations. The usual recommendation is to repot plants to the next nominal size to make it easier to maintain the plant. Putting it in too large a pot may lead to overwatering, which is the No.1 cause of houseplant death.

Houseplants are human assignments because Mother Nature doesn't recognize them as being part of the natural ecosystem. This puts houseplants pretty much on their own in their relationship with the humans interested in them. So if we move them into a poorly lit, drafty room, and they somehow adapt to that site over time by dropping leaves and slowing growth (known as acclimatization), we should pretty much leave them alone. Light intensity varies dramatically with very little movement around a room. This has been proven many times with a light meter. Moving a plant from under a ceiling fluorescent light to a corner may represent a 25 to 30 footcandle drop in light intensity, or more, which could spell doom for the plant.

SOME movement is good for a houseplant. It tends to build stronger, stockier plants. But hard shaking may rupture cells or tear root or stem tissue, which could lead to death.

Q: As the chill fills the air, it reminds me that soon I will have to move my house plants back inside. Any tips you can pass on to me in preparing my plants for indoors? (Carrington, N.D., e-mail)

A: I would suggest repotting with fresh potting soil, in completely cleaned up containers or pots (or new ones if necessary). Hosing the plants off with a spray of water and following up with some insecticidal soap usually does the trick as well. In situations where my house plants have obviously had the attention of some leaf munchers, I isolate them in a plastic bag with a no-pest strip overnight. That procedure usually works quite well for us.

Q: Do you think that clay pots are better than plastic pots for indoor plants? I just love the look of the terra cotta pots so much better, but I am wondering if I am doing any good for my plants. (e-mail)

A: Concerning clay pots: It is tempting to say that they are better than plastic, but I have never seen a plant grow with any difficulty in either one, as long as there was free drainage. Many people feel the way you do concerning the look of the terra cotta pots, hence their continued success in the marketplace.

Some people like the plastic pots because of their ease in cleaning, lighter weight, and greater color range for interior decorating. The choice is up to the individual.

Q. Last fall I repotted some house plants in some new potting soil. Now when the soil on the top gets dry it starts to get white like the enclosed sample. Can you tell me what the problem is?

I also am wondering if I can spray my iris bed with anything this spring to control the weeds. (Tripp, S.D.)

A. The white you are seeing is salt crystals. Nothing to worry about, unless the plants' quality starts to decline.

Once weeds get started in an iris bed, they are difficult to control. I've dug a couple up in my lifetime to get rid of weeds, and it is not fun.

Q. When I plant flowers in containers the soil becomes so hard the water runs right through and out the drain holes. The plants are not getting the water that they need. 

A. If you add copious amounts of sphagnum Canadian peat moss to the container mix, I guarantee that it will hold water much better than it ever has.

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