The seeds are in the canister, packed behind a porous filter, ready and waiting to take what is being termed the ''raw-space test.''
The payload is small but significant, in the view of horticulturists with the George W. Park Seed Company, who have selected 46 flower and vegetable varieties to blast off aboard the new space shuttle Challenger early next year, possibly in January.
The results of the test could contribute to the designing of food-growing techniques at future space stations.
There should also be some interesting and beneficial side effects for gardeners here on Earth.
Among the vegetable seeds selected for the space venture are basil, sesame, watermelon, tomato, and edible soybeans - all important for a space station hoping to grow enough to satisfy its fresh-food needs on site.
Marigold, portulaca, and salvia are among the more popular flower varieties.
Previous payloads have all gone up in totally sealed containers; the seeds, in contrast, have been packed behind a porous filter so that they will be directly exposed to the vacuum environment of ''raw space'' with its temperature fluctations, changing gravity forces, and radiation.
When the payload returns, the space-journeying seeds will be examined by the scientists at the Park laboratories in Greenwood, S.C.
Then they will be grown alongside other seeds that remained on the ground at the Kennedy Space Center as well as others that were retained in the Park seed-storage facilities.
The horticulturists will be checking for seed-coat integrity (split seeds) germination rates, induced dormancy, vigor, and genetic mutations.
Parks, the company that led the field with aluminum-foil packaging in 1962, hopes to develop still better packaging methods as a result of these tests.
The horticulturists are also intrigued by what might come of seed mutation, the possible result of being exposed to radiation.
Mutants are frequently valueless, but every so often one has turned out to be vastly superior to its brethren.
A mutant passes on its changed form and vigor to its offspring, so a truly improved specimen can become the parent of generations of superior plants to follow. Testing garden soil
The advice has been around for some time: If you want to take the guesswork out of feeding your plants, do what farmers have been doing for decades and get your garden soil tested.
State extension services generally offer soil testing, and while it is done year round, the optimum times are considered to be the fall and spring.
The trouble with such tests in the past, however, has been with the interpretation of the results by the county agents. The same test results could prompt widely different recommendations from different agents.
To overcome this problem, a handful of states have recently turned to the computer for aid.
Computerized - and very expensive - equipment is now available that can analyze the soil sample and then make the basic recommendations, depending on the type of crop to be grown and whether medium, high, or very high production is desired.
Massachusetts is one state that has invested in this advanced technology. Ohio and Minnesota either have adopted or are in the process of adopting the new technology.
Dr. Clarke Nicklow of the University of Massachusetts Extension Service in Waltham predicts that the technology will spread steadily around the country.
Extension services are designed principally to serve the home state, but ''yes, we will accept soil tests from out of state,'' says Dr. Nicklow, who adds that he would prefer to get them in the fall rather than in spring, ''when suddenly everyone wakes up to the need for a soil test.''
(Write to the University of Massachusetts, Soil and Plant Tissue Laboratory, 240 Beaver Street, Waltham, Mass. 02254.) Cabbage for compost
Most green garden waste rots down readily in the compost heap, but cabbage and broccoli stems are an exception.
The answer lies in shredding them, or chopping them up into inch-long pieces before putting them in the compost heap.
Another option: Bury them 6 inches deep in the very bed they came from - or anywhere else in the garden where you do not plan to plant members of the cabbage family nxt year.