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The Bay Gardener

by Dr. Frank Gouin

Bring Your Potted Plants Indoors

But first, repot them

If you are moving plants into your home after they have spent the summer outdoors, make certain that you are not bringing in plant pests as well. Houseplants that have been outdoors frequently become infested with scale insects, aphids and spider mites. It is simpler to rid the plants from insects while they are outside than after they have been brought indoors.

If the plants are capable of tolerating a good heavy hosing, there is nothing like syringing the plants with a strong jet of water. The garden hose is adequate; don’t consider using a pressure washer.

A good, heavy, thorough syringing with a fine but strong stream of water will rid most plants of aphids, mites and plant hoppers. But it will not dislodge scale insects.

Most scale insects on houseplants will be tan to yellow brown. Look for them clinging to stem, petioles and the underside of thick-leaf foliage plants. Heavy infestations should be scraped from the plants using a butter knife, popsicle stick or tongue depressor to avoid damaging the tissues. The plant should then be thoroughly sprayed with a four-percent concentration of horticultural oil or summer oil. These are safe to use and approved for use by organic gardeners. Oils kill scale insects and their eggs by suffocation, and it will also give a shine to the foliage.

Another good practice is to knock the plant out of its pot and examine the roots. If roots are circling the outer edge of the root ball and there is little room for expansion or there is little visible potting medium, the time has come to slash the roots and transfer the plant into a larger container.

To slash roots, take a sharp knife and make four to five cuts through the root mass from the top of the root ball to the bottom. This will force the old roots to sprout new roots at each cut. Another method for stimulating new roots to grow is to pull the old roots from the root mass, thus disrupting the existing root system.

Don’t be afraid. Unless you slash or disturb the old roots, the plants will not initiate new roots into the fresh potting medium.

Next slam the bottom of the root ball on the ground to rid it of old potting medium. Press new potting medium firmly between the walls of the pot and the old root ball. Then bounce the bottom of the container on a hard surface to distribute the new medium around the roots and into any pockets.

Allow about an inch of freeboard between the potting medium and the edge of the container. Water thoroughly until water flows from the bottom of the container. You may need to add additional potting medium after the excess water has drained away.

Vinegar as Herbicide

Q I’m wondering about the effectiveness of vinegar for weeds. I understand USDA has been testing various applications (different concentrations of acetic acid, different kinds of weedy plants). Would something like that work?

–Leigh Glenn

A Back in the early 1990s, I did research with vinegar, acetic acid. To kill weeds with acetic acid, you must apply it at concentrations above 15 percent. Acetic acid is an organic acid that leaves no soil residue. However, it will kill only green succulent vegetation and does not kill roots. Perennial plants with extensive root systems and plants with rhizomes will return.


Ask Dr. Gouin your questions at frgouin@erols.com. All questions will appear in Bay Weekly. Please include your name and address.


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