One of the most frequently asked questions at the recent Horticultural Demonstration and Show at Montgomery Mall was "What shall I do with my Wandering Jew? It has green leaves at the tips but the rest of the stems all the way back to the pot are brown and papery."

This stringiness of wandering Jew is characteristic of that family of plant. The plant should be pinched back regularly before the hanging branches become very long. This practice encourages new growth on the stems near the surface of the pot. you cannot restore the brown stems to life. Cut them off. Use any good green growth at the tips as cuttings; either root them in water and plant them later or insert them in the soil of the same pot to grow and fill in bare spaces in the pot.

Indoor gardeners sometimes write to ask where a certain plant can be found.Where can I buy Elfin Herb? Who sells Pink Polka Dot or Satin Pothos?

A search for plants during the summer is often frustrating. Many stores, anticipating less demand, have not replenished their stocks or have reduced the numbers of kinds of plants they offer. Also, during these months growers are busy propagating quantities of plants to supply the demand that will arise when the indoor gardening season begins in earnest as cooler days arrive.

Furthermore, throughout the year an extensive selection of plants is not always available at plant stores. This is situation that might be changed if indoor gardeners were to ask for greater variety. Requests for desired varieties by name would give growers a reason for supplying them.

A Regular reader asks, "How can I get my spider plant to produce plantlets?"

Much has been writen about trying to induce spider plants to bloom and produce plantlets. Research reported by Purdue University has shown that flowering and plantlet production are affected by day length. Short days, i.e. daylight for 8 hours and uninterrupted darkness for 16 hours daily, greatly increase flower and plantlet production.

The experience of others is that keeping the plant potbound results in the production of plantlets.

A grower of my acquaintance believes that when the plant is ready it will produce plantlets (with good care), regardless of what the gardener does for it.

Grace Su, of Rockville, writes: "The leaves of my Swedish ivy keep turning yellow then falling down. Could you tell me what the reeason is and what I should do?"

Your Swedish ivy has probably had too much water. Make sure that the pot's drainage hole is not clogged. Do not let the plant stand in water for more than half an hour. If the soil has become compacted, the roots may have rotted from lack of oxygen, in which case the plant should be repotted. This is a good time of year to take cuttings; select some of the ramaining healthy portions of the plant and start some new plants for the coming indoor gardening season.

Doris Whitehurst, of Chevy Chase: "My newly purchased croton has tiny thin roots all over the surface of the soil in the pot. Is this normal for this type of plant? I thought I should repot it in a larger pot. It is about 11 inches tall and seems quite healthy on the windowsill in the office where it gets sun almost all days."

To determine if the plants is potbound, turn it upside down and jar the pot against a table or shelf to remove the plant from the pot. If the soil ball is a mass of entangled roots, allowing no leeway for additional growth, reportting is recommended. Use a pot of the next larger size and add fresh soil. Cover the surface roots lightly with some of the fresh soil. Water the plant and set it in bright light but out of the sunlight for a few days.

Terri Lester, of Fairfax Station: "I would like to know a safe and effective way to rid my Zebra Plant of the small scale on the underside of the leaves. Also I would like to know precautions to be taken to be sure that insects are not brought into the house on plants brought in from the patio in the fall."

The safest way to remove the scale from the Zebra plant leaves is to pick them off with your fingernails, or to lift them off very carefully with the point of a nail file or penknife.

Bringing plants into the house before frost will be the subject of a future column. In the meantime use preventive measures such as brisk spray from the garden hose or, if insects are present, use a rotenonepyrethrum houseplant insecticide, following instructions on the container explicitly.