Some types of plants, shrubs and trees will thrive with an extra boost of nutrients in the fall, while others will either ignore them or become overwhelmed with the nudge towards flowering in winter and not do well in the following spring. The thinking among gardeners used to be that, in general, fall was not a good time to fertilize, since plants were about to go dormant. But current thinking has changed, or at least become more specific, with root boosters seen as helping plants make it through the winter with better results in the spring.
There are almost as many types of fertilizers on the market as there are plants in your garden! All contain their own propietary combination of micro and macro nutrients. However, all will contain these three basics:
- Nitrogen - stimulates the production of chlorophyll which promotes leaf growth
- Phosphorus - supports the development of roots, stems, flowers and fruit
- Potassium - strengthens plants' ability to resist disease and strenthens its root system
Read the labels on the fertilizer packaging to learn the breakdown of its contents. Since nitrogen and phosphorus have the biggest effect on what the plant produces above the ground, look to potassium -- which strengthens plants' root systems and lowers their stress levels -- as the most important ingredient for fall fertilizing.
Fertilizers can be applied effectively in a variety of methods:
- Slow Release - easy application, just sprinkle granules around plant base and let water and worms do the rest! Nutrients break down slowly and can last up to six months.
- Side Dress - applied in rows along the garden, avoiding stems and crowns; works into soil.
- Top Dress - applied all around the root base and mixed in with existing soil.
Perennials are usually planted in groupings and are vying for the nutrients and sunshine that are up for grabs in your garden. Fertilize perennials in early fall, so they have time to absorb nutrients and build strength for producing buds in the spring. Shrubs and trees can be fertilized in late fall, giving their root systems a good foundation for making it through the winter.
Don't go overboard! Fertilizer and plant labels provide a wealth of information. And being too generous with fall fertilizing can create leaf burn and ultimately do more harm than good. You are fertilizing the root systems in October through early November, not the leaves. Some plants are in much less need of fertilizing, are particularly hearty and may not benefit from the extra attention. These are yarrow, butterfly weed, dianthus, sea holly, hyssop, false indigo, red hot poker, lavender, coneflower, speedwell, catmint, beard toungue, Russian sage, creeping phlox, salvia, stonecrop sedum and ornamental grasses.
Perennials that will benefit the most from adding nutrients in the fall are mums, lupines, lilies, astilbe, tall phlox and delphiniums.
Once temperatures begin to drop, with night time dipping into the 40s and 50s (you'll recognize it as great sleeping weather!), top growth has slowed, but roots continue to maintain plant health and strength. Choose a fertilizer with lower nitrogen levels, since you don't want to stimulate above ground growth. Encouraging root growth and building each plant's strength and endurance in order to produce more buds in the spring are reasons why fertilizing in the fall is a good idea.