Many gardeners believe that bulbs for summer blooms -- true bulbs, tubers, tuberous roots, corms, rhizomes -- should be dug and stored after frost kills the tops. But that's true only of some of them.

Tuberous begonia and caladium tubers and tender amaryllis bulbs should be taken indoors before the first frost. Glad corms can be dug and stored after the first frost. Dahlia tubers, canna rhzomes and Peruvian daffodil bulbs should be dug and stored after the tops are killed by frost.

When dahlia leaves are blackened, immediately cut off stems six inches from the ground and dig. Be careful not to break the remaining stem from the tuber: If this is broken off, the tuber is no good.

Turn the dahlia clumps upside down so the stems can drain, and leave them in the sun the rest of the day. Take them indoors to continue drying for a week or two, then store, unseparated, in baskets of slightly damp vermiculite (or perlite or peat) and cover with newspapers. Store them at 40 degrees to 50 degrees F. Division is done in early spring.

After canna tops are killed by frost, dig carefully to avoid breaking the roots, dry in the shade and store upside down in a cool cellar in peat, vermiculite or buckwheat hulls. Divide them in the spring.

Gladiolus corms can be stored in open trays or hung up in old nylons in a cool cellar. They can be cleaned and divided anytime during the winter.

Peruvian daffodils must be stored in a warm place for at least six weeks after digging for flower buds to form. Do not break the roots.

Tubers of tuberous begonia and caladium can be dug after the leaves turn yellow. If they're growing in pots, simply store the pots in a cool, dry place away from frost. If they're in the garden, dig them with some soil around the roots. Caladium tubers should be stored at temperatures no less than 60 degrees F.

Amaryllis cannot tolerate being frozen, and should be dug in the fall before the first frost. It's important to retain the roots on the bulb from year to year. Store the bulbs in moist peat moss or vermiculite where the temperature won't go below 50 degrees F. After a few months of storage they can be forced indoors as pot plants.

To grow amaryllis as a pot plant, put the bulb in a pot slightly larger than the diameter of the bulb. Plant only half the bulb beneath the soil and water thoroughly. When flowers begin to form, fertilize the plant every other week. t Q: We want to plant some evergreen shrubs that bear red berries to give color to our yard during the winter months. Can you suggest a few? A. American hollies are good, but they may get too big unless pruned regularly to keep them from getting too tall; Chinese Burford hollies are very good; Pyracantha loses most of its berries during winter, but its red and orange berries color in August and September and hold for several months; and Nandina and Aucuba are good in areas where they will survive winter temperatures. Q: I'd like to grow blueberries if it's practical. What are the problems with growing them? A: The main problem is birds. Unless the plants are completely covered with netting the birds may get the fruit as it ripens. Blueberries require an acid soil with a pH of about 4.8. Acid peat moss can be used for this and to provide organic matter, which is desirable for the soil. The peat should be thoroughly mixed with the soil. Q: A gardenia plant was given to me three years ago. It was covered with flower buds, but since then there have few blooms. How can I make it bloom regularly? A: The gardenia sold as potted plants for Easter are forms of Gardenia veitchii. They require a night temperature of 62 degrees F. for flower bud development, and a day temperature about 70 degrees. If the night temperature goes to 70 degrees, buds may form, but they drop off; if it goes below 60 degrees, plant growth may be retarded. This applies only to certain varieties, including those grown as potted plants for the home. Q: In our back yard we have 12 dogwoods that we dug in the woods when they were small. Some are 10 to 12 feet tall and appear to be healthy, but there's no sign of flower buds. What could be wrong with them? A: All healthy dogwoods usually bloom -- and most unhealthy ones also, when they're old enough. Trees growing naturally where they came up from seed may be five to 10 years old or older before they start to bloom. Withholding nitrogen fertilizer to slow down growth may encourage them to start blooming. Q: I dug my vegetable garden last week and have it ready for spring planting. I didn't plant a cover crop. Is there really any serious danger of erosion of the soil? A: In areas where the ground may be frozen or covered with the snow much of the winter, there's not likely to be much erosion. In other areas, it may be better to plant a cover crop of winter rye. The seeds are not expensive and they germinate in a few days. Dig it under in early spring. Q: Squirrels are digging up my tulip bulbs. Is there anything I can do to prevent it? A: Cover the area where the bulbs are planted with one-inch mesh wire. Peg the wire down, and if the appearance bothers you cover it with a thin mulch. Remove it in the early spring. Q: I have an avocado tree eight feet tall, started from a seed. It's in my greenhouse and doing fine. Can I ever hope to get fruit from it? A: The main problem will be pollination. An unusual characteristic of the avocado tree is sex-reversal of the flowers that prevents pollination. In commercial orchards this is overcome by interplanting compatible varieties to insure cross-pollination. Q: Will ammonium sulfate harm the beneficial bacteria in my garden soil? A: There's no evidence that ammonium sulfate will harm beneficial bacteria. On the contrary, both the ammonium nitrogen and the sulfur supplied by this product might enhance bacteria growth. Q: Is sawdust all right to use to mulch my roses? Will it make the soil too acid? A: Sawdust is an excellent material to use as a mulch for roses, strawberry plants, berry bushes and shrubs and for vegetable and flower gardens. The sawdust reduces crusting of soil, conserves moisture, helps rainwater move into the soil and provides some control of weeds. Contrary to popular belief, sawdust does not make the soil acid. The final effect of sawdust is to help maintain or slightly increase the alkaline reaction of soil. s