QUESTION: Our lovely, healthy oakleaf hydrangea and the bigleaf one near it never bloom, though they put out lots of new shoots each spring after their winter dieback. They get bright sun part of the day and filtered sun for the rest. What's wrong?

ANSWER: These hydrangeas bloom from old wood. If they keep dying back to the ground, they will remain flowerless no matter how many new shoots they make.

Bigleaf (Hydrangea macrophylla) is a Zone 6 plant. Oakleaf (H. quercifolia) is rated to Zone 5. But though both can sometimes survive where they should fail, both can also die back where they should flourish.

If the plants are exposed to strong winter winds, try wrapping them with burlap. Or move them to a more sheltered location. If these protections don't work, it's too cold; macrophyllas are out.

But do try planting other oakleafs before you give up. Dwarf forms have a better chance of benefiting from snow cover, while the straight species is sometimes hardier than cultivated varieties.

If you get lucky, the payoff is huge flower clusters, in addition to handsome leaves, great fall color and appealing winter bark.

While you are planting, don't forget old-fashioned peegee (H. paniculata) and hills of snow (H. arborescens). They are less refined than oakleaf types, but they are hardier and bloom on new wood, so dieback is seldom a problem.

And you may want to try Endless Summer, a new hybrid bigleaf that is marketed as able to bloom on both old and new wood. Its true splendors remain to be seen, but the cold-climate macrophylla-deprived are greeting it with glad cries.

Sources for hardy hydrangeas include Forestfarm, 541-846-7269 or forestfarm.com; and Arrowhead Alpines, www.arrowheadalpines.com or 517-223-3581.

Endless Summer is available at well-stocked nurseries.

QUESTION: I have window boxes on the second floor of my weekend house on the ocean. Trying to get plants to survive in them has been a nightmare.Please suggest some that bloom in semishade and don't need water during the week.ANSWER: No wonder your dreams are disturbed; not many plants can meet such a daunting set of requirements. But if there is enough soil (boxes at least 10 inches wide and deep), and if you add water-retaining granules to help it stay moist, there may be hope.How much hope depends on what you mean by semishade and how close you are to the water. Drought-tolerant bloomers tend to be sun-lovers, while plants that flower in the shade are inclined to need plenty of water. And few indeed are the flowering plants that are big fans of salt wind.Consider using this year to conduct survival trials. In every box, plant one or two each of browallia, torenia, hardy geranium (cranesbill), lamium, nasturtium and vinca. Plant several kinds of tender geranium (Pelargonium), including zonal and ivy-leafed. Try a few Non-Stop begonias in any boxes that are out of the wind.None of the plants will be at its best under your conditions, but it is likely that at least a few will put on a respectable show. If you keep records and take a few snapshots, you will know what you can use to make a pleasing design next year.QUESTION: As usual, our tomato plants are loaded with big green fruits that won't ripen before killing frost. Our success at ripening them on the windowsill has been mixed to poor. Are there any special tricks?ANSWER: Tomatoes must mature on the plant to ripen well after picking, so focus on those that are starting to turn color, or at a minimum are pale rather than dark green.Keep them away from the windowsill, where they will be alternately too hot and too cold. Ideal ripening temperature is about 60 degrees. Up to 70 is fine, below 50 is not.Keep the fruits separated, spread on trays or individually wrapped in newspaper. Check them frequently and remove any that show signs of decay. Early fruits keep better than late ones, fruits from healthy plants far longer than those from plants with disease.Wrapped tomatoes ripen more rapidly than those that are exposed to air, and tomatoes enclosed in a paper bag with one or two half-ripe bananas will ripen even faster. The accelerator is the ethylene gas given off by the fruit.Address questions to Garden Q&A, The New York Times, 229 W. 43rd St., New York, N.Y., 10036, or by e-mail to gardening@nytimes.com. Those of general interest will be published. Unpublished questions cannot be answered individually.By N.Y. Times Service