UNITED STATES—No more fertilizer! . . . almost. The main exception is turf that might need a bit of fertilizer if it must stay green through the coldest part of winter, but that is another topic for later. Otherwise, most plants start to go dormant through autumn, and should be as dormant as they get by the middle of winter. Fertilizer later than now could be as logical as espresso just before trying to get to sleep.
Keeping marginally frost sensitive plants up past their bedtime can have serious consequences. Lemon trees are not often damaged by frost in the mild winter weather here. That is because they stop growing through late summer, and the last of their new foliage matures before autumn. Fertilizer applied too late can stimulate late new growth, which is more likely to be damaged by frost.
Plants that like a last application of fertilizer as late as the end of September, such as roses, use it for their last minute preparations for dormancy. It actually takes a bit of effort to abscise (shed) foliage. Besides, healthy foliage is easier to abscise than distressed foliage is. Well fed roots, although significantly subdued by dormancy, work later into winter, and get an earlier start in spring.
Roses are, of course, not as likely to be damaged by late application of fertilizer as lemon trees are. They know better than lemon trees do about what to do when the weather gets cool. They just go dormant. Much of the extra nutrients get ignored as they leach through the soil with winter rain. Many of the nutrients become insoluble and unavailable to plants as winter weather gets cooler.
Autumn is the season for allowing most plants to slow down and get ready for winter dormancy. Trying to get them to be as green and productive as they were in spring can do more harm than good. Only plants that are active through winter, such as cool season vegetables, cool season annuals, and some types of turf, might appreciate moderate applications of fertilizer. If newly installed plants want fertilizer, they should get only enough to keep them happy until they get more next spring.
Highlight: mulla mulla
The common name sounds funny, but it is easier to pronounce than the Latin name. Mulla mulla, Ptilotus exaltus, is an Australian species that has been locally available longer than its limited popularity suggests. It may seem to be more peculiar than it is because it is grown primarily by specialty growers, who happen to grow many cool plants that should be more popular than they are.
Like many species that are grown as annuals, the mulla mulla is really a short term perennial that can perform for a few years, but is unfortunately more often grown as a warm season annual. It will finish blooming soon, but if left in the garden through winter dormancy, young plants should resume in about April or May. It can succumb to frost if the weather gets cold enough through winter.
Although it can survive with less, mulla mulla prefers somewhat regular watering, and good sun exposure. New spring growth develops rather vigorously without getting much more than half a foot high and wide. Fuzzy cylindrical blooms that stand above the foliage are about three inches long. Floral color is pinkish mauve, with a silvery sheen. Deadheading promotes subsequent bloom.
Horticulturist Tony Tomeo can be contacted at tonytomeo.com.