Fertilizer provides much of the raw material (nutrients) that allows plants to keep their systems in order, to manufacture their own food, and to grow. Without the essential nutrients present in the soil and available to the plant, plants will rob them from other tissues and exhibit symptoms of a nutrient shortage. In containers, you'll often see older leaves yellow & fall from a lack of nitrogen. The plant is actually extracting the mobile N from older leaves, sacrificing them in effect, to supply it to newly emerging leaves. Nutrients that are not mobile, will often manifest symptoms that indicate a shortage in new leaves.

As long as a plant is actively growing, it will utilize the nutrients in fertilizer. As temperatures drop below 50* F, the plant slows growth & thus its use of N. When plants are not using N, it is better to keep its concentration lower. It can feed the bacteria that causes root rot and it also feeds the bacteria that breaks down the structure of the soil.

For containerized trees & shrubs I usually alternate feedings about every 2 weeks with 5-1-1 fish emulsion then 20-20-20 MG, Peter's, or a similar product. As temperatures begin to cool (in Sep in my zone) I eliminate the N from my fertilizer program and change to a 0-10-10 blend of either fish emulsion or a chemical mix. Because I use an organic 5-1-1 in my summer program, there is ample residual N in the soil as winter approaches & the plants fare very well on the altered diet. I can see no difference between chemical fertilizers and organics. Both work well in containers.

In spring, if you are looking for maximum growth, fertilize as leaf buds are opening or for conifers, as candles begin elongating. If you wish your plants to remain more compact, hold spring applications until leaves have formed & matured or candles have stopped elongating & are open. This will keep internodes short, leaves smaller, and provide nutrients when the tree is concentrating on cambial (girth) and root growth.

I am seeing frequent advice to use grass clippings only, as fertilizer in containers. I'm sorry, but if it was an effective method of nutrient delivery, because the supply is unlimited and free, every greenhouse or nursery operation in the world would be stuffing their containers with grass. One of the main attributes of a sound fertilizer program is the growers control over delivery timing and quantity/type of nutrients. Obviously this is lacking in the grass clipping suggestion. There are additional issues that would be associated with the practice as well.

Good luck.

Al

Controlled release fertilizers release nutrients slowly (if at all) when the weather turns cold. The 3-4 months the fertilizer is supposed to last is based on perfect conditions (70-80 degrees). They will release faster in the heat, slower when its cold. Watering frequency could have an effect on rate of release as well.

I usually add more Osmocote in August...my growing season usually extends into November.

And I agree with Al--container plants will not do well on grass.

Jason

Good point about the controlled release fertilizer. Wish I'd thought of it.

Al