Q A guest brought a dozen roses from the florist, and I arranged them immediately in a tall vase. Before the evening was over, however, the heads of eight of the roses had drooped. We might have thought that they were stale except that they were in bud. What could have caused this?
The stems of roses and certain other flowers, such as Dutch iris and large mums, will sometimes seal over, or the ends of the stems may become blocked with air so that water flow is impeded.
Any cut flower should have about an inch of its stem cut off, diagonally, with a sharp knife before it is put in warm water.
Placing the base in a cool spot for a half hour helps the flowers take up the warm water and also causes the cells to expand. However, if the heads flop over, don't give up. Cut off another half inch of stem and place in 3 or 4 inches of water that is warm enough to be tingly to the fingers.
Set the flowers in a cool spot (near 50 degrees F., if possible), and the chances are that the heads will pop back up within an hour.
Q I always supposed that insecticides made from plants were harmless to pets and people. Now a friend tells me that some insecticides, such as rotenone, can be very harmful. What do you say?
Rotenone's properties were discovered in South America when natives were seen using the root of a plant called Derris (D. elliptica) to make fish float to the surface for easy harvest. It's also harmful to beneficial insects, and spraying on blossoms should be avoided because of damage to bees.
Although our modern chemical pesticides are more potent, care should be taken when using any type. Do keep them away from pets and children.
Vegetables and fruit should always be washed thoroughly to remove sprays, whether grown in the garden or bought from a store.
Q Last July my tomato plants wilted, and I wrote to you asking for advice. You diagnosed the difficulty as fusarium wilt and suggested planting next year's plants in a different spot. You also recommended that I plant resistant varieties. How do I know which varieties are resistant? If I plant other vegetables where the tomatoes were last year, will they also get the wilt?
Fusarium doesn't bother other vegetables. We now have many tomato varieties that are resistant to both fusarium and verticillium, listed in catalogs as VF or VFN after the name of the tomato.
The ''N'' signifies resistance to nematodes. You may also see a ''T'' or an ''A,''or both. These signify tobacco mosaic and alternaria wilt resistance.
Q Since we have lots of autumn crocus, I was interested in your explanation of the difference between saffron crocus (lavender with red stigmas) and mystery lily, not a crocus but lavender colchicum, which may be toxic. My gardener husband further comments that stigmas from some saffron crocus taste musty, and also that they are tricky to grow, sometimes getting only one bloom per five corms.
Only Crocus sativus is the true saffron crocus. There is another lavender crocus with red stigmas (C. medius), but it does not have the saffron taste. You can be sure you have the true species by ordering from a reliable bulb company.
All crocuses, including C. sativus, need a sunny spot and well-drained soil. Your husband is right. No one should think of saffron crocus in a home-garden situation as 100 percent failproof.
Q We had pink phalaenopsis orchid for three years, and it bloomed each year for several weeks. Recently the leaves turned brown, then blackish; lopped over; and the root rotted. The only difference in care was that we left it on our sun porch this fall, which dropped to 50 degrees F. (10 C.) at night. Usually we have moved it to our kitchen for the cool months. We found no insects on the leaves or in the growing medium.
Phalaenopsis cannot stand a temperature below 60 degrees F. (15 C.) for any length of time. The range for night temperature should be 60 to 70 degrees F., daytimes in the low- to mid-70's. Extremes in temperature (low or high) will cause bud drop. Protect from the bright sun.
Don't forget the World Orchid Conference to be held in Miami March 5-12, 1984 . It's sure to be spectacular.
Q I love those miniature French pickles called cornichons and find recipes for making them in various publications. I want to grow my own cucumbers, but cannot find any reference as to where to buy seeds of miniature cucumbers.
Nichols Garden Nursery, 1190 North Pacific Highway, Albany, Ore. 97321, lists them in its catalog under Pickling Cucumbers: Cornichon De Bourbonne.
The catalog goes on to say: ''Make tiny sour cornichon pickles to eat with your pate, meat loaf, and cold cuts. Recipe included. You need fresh tarragon.'' This herb is also included in the catalog.
If you have a question about your garden, inside or out, send it to the garden page, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115. Doc and Katy Abraham are nationally known horticulturists, authors of several books on gardening, and greenhouse operators for more than 25 years.