- Author: Susan Flaherty
What do the numbers on fertilizer sacks indicate?
The “big three” nutrients show on bags are nitrogen, phosphate, and potash which provide N, P, and K elements. They are the ones declared on a bag of fertilizer. If you see the combination of 5-10-5, it means that the bag contains 5% nitrogen, 10% phosphate, and 5% potash by weight. These aren't in a pure form but with other material.
How do each of the “big three” fertilizer elements help a plant?
1) Nitrogen is an essential element of chlorophyll that helps a plant produce starches and sugars. Since nature seldom provides it in sufficient quantities, fertilizers are used to augment what is naturally available.
If a plant is deficient in nitrogen it will be small, the older leaves turn from green to yellow, then finally brown but remain attached to the plant. Stalks are slender and few new ones develop.
2) Phosphorous is associated with cell division. It contributes to stiff stems, flowering, and seed production. In acid or alkaline soils it becomes unavailable to plants so it is important to manage the pH of the soil for efficient uptake as well as providing adequate amounts of supplemental phosphate. Fertilizers bags show the amount of phosphorus content in terms of percent rock phosphate (P2O5) for historical reasons.
Phosphorus deficiency causes the whole plant to be dwarfed. The foliage is a dark. dull green, and often the stems turn purple. Areas between the leaf veins also can become purple, while the edges turn yellow. Loss of lower foliage follows.
3) Potassium is essential for movement of the sugars in the plant, the utilization of nitrogen, root development, and it also hastens maturity. It can be depleted over time in soils as plants grow.
A potassium deficiency results in the leaves becoming mottled with yellow between the veins, then turning brown and dropping. Plant growth will be stunted. Potassium in fertilizers is measured in potash form (K2O).
What is the best fertilizer for perennials and annuals?
The best fertilizer is the one that provides just enough of the elements lacking in the soil and no more. A balanced fertilizer—one with no zeros in the analysis like 15-5-10—will usually work.
Should I buy organic fertilizer?
The “big three” elements in organic fertilizers can be highly complex and are unavailable to plants until they have been broken down into simpler forms by soil organisms. Since these organisms are partially dormant at temperatures below 60 degrees and grow progressively more active up to 90 degrees they are not very effective in early spring. However, some add organic matter, an advantage not provided in synthetic or mineral fertilizers.
In either type of fertilizer the plant nutrients must be in a usable form before they can be used by the plant. This process of conversion happens naturally based on environmental conditions for both types, but organic materials are usually slow to release.
The choice is also driven by one's philosophy toward gardening.
My friend has horses and will give me manure. What should I know about using it in the garden?
It can be a valuable soil amendment. One caution: Many owners use pesticides to control insects or parasites, or feed hay that has may have been treated with an herbicide, so manure should be well composted in a separate pile before being applied to the soil. Cow manure can be a valuable soil amendment if allowed to rot in a compost heap during the winter in preparation for spring use. Check out: http://smallfarms.oregonstate.edu/sfn/f09Herbicide In the Eastern Sierra we tend not to have issues with local animals.
Remember that un-composted manure can carry human pathogens. You should take measures to ensure that plenty of time passes before harvest after using raw manures.
When should one apply fertilizer?
For permanent plantings such as trees, shrubs, evergreens or perennial flowers , fertilizer may be applied in the fall or spring with equal success. For annual flowers or vegetables it is recommended that fertilizers be applied just prior to planting.
- Author: Jan Rhoades
To provide a good home for our plants we need to incorporate some organic matter, usually compost – but not an overload – just the right amounts over time contribute to long term soil fertility, good soil structure and increase the soil's capacity to hold water and air.
All those amendments have their place and their purpose. What are you looking for? How much do you need? How is this product applied? What's in it? Keep in mind that this is an annual event, or even a seasonal event if your gardening season is long and you plant crops successively. Someone once said, “Begin with the end in mind.”
There are organic fertilizers such as compost, aged manure, rock phosphate, soybean meal, and fish meal, and there are inorganic fertilizers that are available either as a single nutrient or multi-nutrient product. These fertilizers can be slow release providing nutrition over time or soluble like an athlete's energy drink, providing quick nutritional value.
Most soil has some residual nutrients, however, only a soil test can assess what is there. Fertilizing without the results of a soil test is like eating everything in the pantry hoping to get the nutrition you need. Additionally, this practice can exacerbate an existing problem or imbalance. A soil test will also tell you the pH which, if too high or too low, can affect the uptake of nutrients present in the soil.
A soil test is a good place to begin to understand what kind of amendments might be needed to build your soil. Generally, DIY kits are not as reliable as sending a soil sample to be analyzed by professionals.
We all want to be thrifty, however, there are a few things you should never add to your garden soil:
- Un-decomposed wood chips or sawdust – these materials are high in carbon but lack enough nitrogen to decompose quickly – so they use up nitrogen that plants want and need.
- Fresh manure can harm plants due to elevated ammonia levels. – Use only aged, composted manure that has reached at least two heating cycles (130-140 degrees F) Also, know that nitrogen levels in composted manure are low and phosphorus and potassium levels are higher – so adjustments will have to be made. Also, salt levels will be higher.
A good way to remember all this is that fertilizers feed plants and compost feeds the soil. Nutrients alone cannot keep plants healthy if they are living in poor soil. Compost improves the mobility of air, water in the soil, and makes nutrients more available to plants.
Finally, there is such a thing as too much compost and too much fertilizer. Armed with the results of your soil test, you will be able to make wise choices about what to buy, how much to use, and when to apply it. When in doubt, a good quality all purpose composted soil amendment and an all purpose fertilizer are probably a reasonable way to get started. Of course, be sure to use them as directed on the bag.
For more in depth information on soil and composting be sure to use the links on the website. This year, biggest tomatoes ever – right??