Fertilizer, in simple terms, helps plants grow. It provides a bit more of what growing plants crave. In some situations, it compensates for nutrient deficiencies. Fertilizer can be organic or synthetic. Various formulations serve a variety of purposes. Custom formulations appeal to plants with discriminating taste, such as citrus, orchids and roses. Slow release fertilizer lasts for a month or two.
Of course, proper scheduling of the application of fertilizer is very important. Fertilizer can actually become toxic with excessively frequent application. Fertilizer that provides significant nitrogen to promote vegetative growth after bloom can inhibit floral growth prior to bloom. Fertilizer that promotes root growth for new plants is unnecessary for mature plants. The diets of plants are variable.
Summer lingers later here. Regardless of the weather, it is now autumn. This is when deciduous plants start the process of defoliation for their winter dormancy. Evergreen plants are less obvious about their winter dormancy. Some remain active and even bloom through autumn and winter locally. Nonetheless, cooling weather and shortening days inhibit vascular activity of almost all plants.
Except for cool season vegetables and bedding plants, not many plants benefit from fertilizer applied this late. New plants might appreciate a bit just to help them adjust to their new environment. Some deciduous plants, particularly roses, like a last late application of fertilizer as they get ready for their long winter dormancy. Lawns might want fertilizer this late or perhaps later to stay green.
Otherwise, it is getting late to utilize fertilizer.
Late application of fertilizer can be very detrimental to plants that are sensitive to cool weather. Such plants typically finish growing through summer. By autumn, their mature foliage and stems are either resilient to minor frost, or are dieing back (defoliating) for winter dormancy. Fertilizer can stimulate premature development of new growth that will be much more sensitive to even mild frost.
For many of us, this might seem to be irrelevant. We do not apply fertilizer to our landscapes and gardens. Some of us who use fertilizer do so mostly for seasonal vegetable plants and flowering annuals. Such plants will either not be around long enough to get fertilized again this year, or are cool season plants that are on a completely different fertilizer schedule through autumn and winter.
Two other main exceptions that that might continue to get fertilizer after summer are lawns and houseplants. Some types of turf grasses, particularly those in older lawns, can get a bit pale through the the cooler parts of winter, so appreciate a boost. Houseplants are mostly immune to the cold weather outside, so continue to to crave nutrients, even if slowed somewhat by shorter day length.
So, except for lawns, houseplants, and incoming and outgoing annuals and vegetables, most other plants in the garden do not need to be fertilized again until weather begins to warm next spring. Not only do they not need fertilizer, but some could be inconvenienced by it. They know what time it is, and that they should now be slowing down for winter. Fertilizer can interfere with the process.
There are a few reasons why plants slow down or go dormant through winter. Some of the nutrients that they need to maintain active growth are less soluble or otherwise less available to them at cooler temperatures. There is less sunlight too. Plants from climates with cooler winters tend to be more proficient with winter dormancy. Many are deciduous to limit damage from wintry weather.
Some plants might use a late application of fertilizer to get ready for winter dormancy. Others might just ignore it as it leaches through the soil. Those that are from milder climates might try to use it to continue growing later than they should. For plants that are potentially sensitive to frost, growth that develops too late will not likely mature soon enough to be resilient to even mild winter frost.
This is why fertilizer can be applied to many plants one last time about now, but no later.
Autumn is for planting . . . but not much else. While it is important to get certain new plants into the garden before cool and rainy weather, other gardening chores will not be necessary while plants are becoming less active before winter dormancy. Raking falling leaves is probably the biggest of the new chores that are specific to autumn.
Formal hedges that have been getting shorn regularly since spring may not need to be shorn again until next spring. They simply will not grow much between now and then. If possible, pittosporum and photinia should not be shorn once the weather gets rainy. Their freshly cut stems are more susceptible to certain diseases while wet than during dry weather.
Citrus and tropical plants should not be pruned late because pruning stimulates fresh new growth that will be susceptible to frost later in winter. Even if tender new foliage does not get frozen, it can get discolored and disfigured by cold weather. Cool weather inhibits vascular activity necessary to sustain the development of healthy new foliage anyway.
For the same few reasons, fertilizer will not be necessary later in autumn. Fertilizer can potentially stimulate new growth when it is not necessarily wanted. Also, some nutrients in fertilizer are less soluble (or chemically unavailable) while the weather is cool. Only plants that grow through winter, like cool season annuals, vegetables and grasses, will want fertilizer.
Planting is done in autumn because plants are either dormant or less active than they had been during warmer weather. They can take their time to disperse their roots into comfortably cool and damp soil. Evergreen plants do not draw as much moisture from their roots while foliage is cool and damp. Deciduous plants draw even less moisture without foliage.
Spring blooming bulbs get planted in autumn not only so that they can disperse their roots leisurely, but also because they need to get chilled to bloom well. Bulbs can be phased, so that those planted earlier will bloom before those of the same kind planted later. However, if planted too late, they may not get sufficient chill.
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.
‘Fertilizer’ is a polite term for ‘recycled vegetation’.
‘Recycled vegetation’ is a polite term for something else.
This is not a synthetic type of fertilizer that gets tossed about or poured on. It gets added to compost and allowed to compost some more before being spread out as a mulch over the surface of the soil, just before chipped vegetation gets dispersed over the top. Alternatively, it sometimes gets mixed into the soil. It is quite useful. You can’t beat the price.
It is recycled differently from the compost or chipped vegetation (from a brush chipper). It is recycled through a horse, or more specifically, two horses. As the picture above suggests, it begins at the front of the horse, and ends at the rear of the horse, which is not pictured.
The horses happen to be quite efficient at recycling vegetation. They do it all the time. They are probably doing it right now. I would describe the process, but I do not know how it works.
Three times weekly, on Mondays, Wednesdays and Fridays, some poor sucker must go to where the horses live and work to collect the binned ‘fertilizer’, and deliver it to the compost pile. By the time it gets mixed into the compost, and composted more, it is not recognizable. Otherwise, it might be a problem in the parts of the landscape where it gets dispersed with the compost.
The landscape seems to like it. Only a few plants with special needs get any sort of synthetic fertilizer.
This sort of recycling is not new technology. It has been around as long as horses have been serving humans. In fact, it was not even invented by humans. Horses were doing it long before humans merely discovered, refined and took the credit for it.