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We have never given our shade trees any fertilizer. Are we correct in assuming they should be fed just like any other plant? If so, how often and when is the time to do it?

You are correct. Shade trees are a tremendous asset, adding considerable value to your home, besides cutting down on noise, lowering the temperature in summer, and acting as a barrier against cold in winter. In addition, they act like giant filters, reducing pollution in the air and giving us oxygen in return. Feeding them once a year is good business. Anytime from early spring until mid-August is a good time. Later than this, new growth might make them susceptiple to winter cold.

Any balanced fertilizer can be applied underneath the dripline of the branches. A good way to apply is to punch holes with a crowbar about 18 inches deep and about two feet apart, around this circle. A gallon of liquid plant food per hole (mixed according to directions) can be used, or you can apply dry fertilizer at the rate of one pound for each inch of trunk circumference. Divide the poundage evenly between the holes.

Fertilizer spikes and slow-release fertilizers are also on the market. Read directions before using.

The leaves of our blueberry bushes are turning yellowish with greenish veins. We scattered peat moss around the roots when we planted them last year and we have fed them a regular fertilizer, but it doesn't seem to help. Our soil is quite sandy.

Blueberries need a very acid soil (pH of about 4.5). The symptoms you describe indicate your soil is not acid enough.

Your County Cooperative Extension agent will test the soil and tell you what pH you have. Then you can use a formula for acidifying sandy soil.

The following amounts are for 100 square feet of soil. If the pH is 5, add 2. 4 pounds of aluminum sulfate; if it is 5.5, add 4.8 pounds; for a pH of 6.0 add 7.2 pounds.; if the pH is 6.5, add 9 pounds; and if the pH is 7, add 11.4 pounds.

The aluminum sulfate should be spaded into the ground carefully around the plants.

For a clay soil the amounts of aluminum sulfate should be increased about 2 1 /2 times the above amounts. Also, add a mulch of sawdust wood chips or oak leaves of 4 or 5 inches. Roots are shallow and mulches help to retain moisture around them.

Tiny black insects that hop like fleas are riddling the leaves of our potato plants with hundreds of little holes. Is there a type of flea that attacks plants? How can we get rid of them?

What you have are flea beetles, not related to fleas but bearing their name because of the way they hop. They usually appear when plants are young, then disappear as quickly as they came.

Chemical gardeners use Sevin to control them, but if you want a natural control you can dust with wood ashes or talcum powder.

Friends have a plant they bought at a roadside stand which is covered with flowers that look like miniature orchids. They said the name on the label was ''Poor Man's Orchid.'' Could you give some information about this plant? I cannot find it in any of my garden catalogs.

The plant is schizanthus and is listed in many catalogs. It can be grown outdoors as an annual or indoors as a potted plant. From seed, it takes five to smx months to bloom profusely.

Seeds produce plants with shades of rose, purple, gold, red, salmon, violet, white, yellow, and pink. The plants are notd to care for, and directions should be on the seed packet.