I'd love to know how you fertilize your container-grown plants. This is directed in part to tapla, who I know has thought this through, but also to the rest of you. I definitely under-fertilize , . . and I'd like to make amends, without spending a fortune.
fertilizing container-grown plants
I get asked this question frequently, or a variation like: "I want to feed my plants the best - what's best & how often should I feed?". Most people queried, would look right past the question and hand you a box or direct you to the fertilizer section of a plant store for "plant food".
Actually, you cannot feed your plants. Food provides energy - fertilizer does not. Plants manufacture their own food during the process of photosynthesis when the pigment chlorophyll traps the energy of the sun in a molecule of carbon dioxide and water. The result of this miraculous reaction, without which the earth would be uninhabitable, is a molecule of glucose - sugar - a carbohydrate - photosynthate. The molecule acts just like a battery, storing energy from the sun that can be translocated to all living plant parts for immediate use, or stored in living cells - roots, leaves, and cambium for later use.
In order for a plant to make and use food efficiently, certain elements need to be available to the plant. In fertile garden soil, it is likely, even probable that that the nutrients will be available in a usable concentration. In container culture, it is a virtual certainty that we will have to accept the responsibility for providing nutrients in usable concentrations for the term of the planting if we are to expect plants to grow at or near their potential genetic vigor.
The three main elements or compounds that are needed for plant metabolism are nitrates, phosphates, and potassium (NPK), and they represent the bulk of ingredients in balanced fertilizers. We term these ingredients macro-nutrients, sometimes referred to as “the majors“. Also included in the macro-nutrient category, but necessary in lower concentrations are magnesium, calcium and sulfur. Rounding out the list of nutrients needed to keep plants healthy are the micro-nutrients, or “the minors”. These nutrients include iron, boron, zinc, copper, manganese, molybdenum, chlorine, cobalt, and nickel. Please note that some of the minor elements, or micro-nutrients are required in such minute amounts that deficiencies are rare in garden soils, but more common in container media. For that reason, it is good practice to insure that you use a fertilizer that is complete, including the minors. If the minor nutrients are not listed on the fertilizer package, and you’re unsure that your soil contains an adequate supply, an excellent way of providing the minors while furnishing major nutrients is to use a granular soluble or insoluble product (e.g, STEM or Micromax). Organic fish and/or seaweed emulsions as part of your supplementation program can also be effective, but here I'll concentrate on the major elements.
Now that we've have seen that fertilizer is not plant food, but a way of delivering some of the raw materials or building blocks that plants need to make their own food and keep their systems orderly, I'll briefly say that it is important that we insure the soils we use contain adequate/appropriate volumes of air and water so as to make nutrient uptake possible and efficient, but that is another subject I won't dwell on today.
You can probably use a schedule or timetable to fertilize plants & have them be reasonably happy, but I use a different approach. If you do choose to fertilize on a regular schedule, it makes no sense to continue to fertilize when plants are quiescent due to chill, heat, or other unfavorable cultural conditions, Under these conditions, you might extend the preset intervals. Plants need more nutrients when robust and actively growing and less when they are "coasting".
I use a two-pronged approach to my fertilizing. The first thing I do is note leaf color of older leaves. N is a very mobile nutrient in plants. When it is deficient, plants "rob" it from older leaves to use in the production of new vegetative growth. So, when I see a lightening of leaves toward a lighter green or yellow, especially older leaves, and I'm sure that other cultural conditions are what the plant requires for good vitality, it indicates to me a need for supplemental nutrients.
A simplification of how I fertilize is: I attempt to get a higher percentage of N to foliage plants or those that are being grown for a reason other than blooms or fruit. Highly nitrogenous fertilizers support the plant during the growth of leaves and foliage. For flowering/fruiting plants, the phosphatic portion of fertilizers aid flower/fruit production, so I'll usually include the intermittent use of a fertilizer with higher percentage of P. Potassic compounds (K) stimulate the growth of roots and are included in adequate percentage in all complete fertilizers I use.
I use both chemical and organic fertilizers. As noted, but worth repeating, I determine the need for fertilization by leaf color. When leaves lighten and fertilizer is needed, I mix a recommended full strength solution of 20-20-20 soluble granular fertilizer and add a full strength solution of 5-1-1 fish emulsion in the same mix. This mix, I'll apply to foliage plants & plantings that are not dependent on blooms for their beauty. This is pretty much my standard for these plantings. For blooming plants, I'll use the same 20-20-20 fertilizer with a 2-3-1 fish emulsion included - UNLESS leaf color is good. If leaf color is good - I'll substitute a bloom-inducing, soluble formulation like 10-52-10 or 15-30-15 and still use the 2-3-1 emulsion. In all cases, I'll apply these solutions to well-hydrated plants growing in moist or damp soil, thoroughly saturating the entire volume of soil in the container.
I prefer the reliability and immediate action of the chemical soluble fertilizers for results, but understand the wont of some to remain organic. Generally speaking, organic fertilizers do release nutrients over a fairly long period, but there is a potential and considerable drawback in depending solely on them. They may very well not release enough nutrients to give the plant what it needs, when it needs it for best vitality. Organic fertilizers depend on soil organisms to break them down into elements the plant can assimilate, so most of them are effective only when soil is moist and soil temperature is warm enough for the soil organisms to be active. This soil organism population is a boom/bust proposition in container soils due to the extreme variables of temperature, moisture and pH. Nutrients in chemical form are immediately available for plant use and exhibit no dependency on soil biotic activity for availability. Plants do not care whether their elemental building blocks are provided in chemical or organic form.
Well, I certainly never intended to go on so long; and I know I bored some into leaving before they got this far, but for those that made it to the end, I hope my thoughts were clear enough to provide some insight.
Al Fassezke
This message was edited Feb 3, 2007 4:15 PM
This message was edited Feb 3, 2007 6:52 PM
Thanks once again Al...I just have to learn not to over fertilize my plants....Sure wish I knew how to put a link on here...for your soil mixtures!!!
happy - macomb....You might want to read Als soil mixtures at post #1608726...
Demstratt: Thanks! Here's the link to Al's soil mixture: http://davesgarden.com/forums/t/527353/. Actually, I had dmailed Al after reading that post, which is what triggered this thread!
Al: You indicate that you stir a good big of time release fertilizer into your planting mixtures. After that is used up, do I understand that you do not replace it as such, but just follow the above protocol?
Hi, Happy_M. I usually recommend that folks building their own soils add a CRF to the mix, and I often add it to help ease my fertilizing responsibilities early in the summer when I'm most busy in the gardens and with bonsai plants. It certainly is not necessary though; and in many instances I forgo its use. If you wish to minimize expense, don't mind the little extra effort it takes to mix & apply solutions, and think the program outlined above has merit, just skip it (the CRF).
Al
Thanks. My question is different. I want to ease fertilizing responsibilities on an on-going basis. So once the CRF has worn off, do you just stir more into the top of the soil?
Thanks happy....A few friends on another site wanted to see Al's soil mixtures!!!
You can do that, yes; however, CRF is not as effective and does not yield as consistent a dosage when broadcast on top of soils. It is dependent on temperature and dissolution in both condensate and irrigation water for delivery of nutrients. Mixing into the upper surface is better than strictly broadcasting after the initial supply you included when you first composed the planting or soil is depleted.
Sorry I missed your meaning.
Al
All you information is so helpful -- I really appreciate it! So what do you do when the CRF runs out? Do you just rely on non-CRF fertilizers go-forward?
For years whenever I plant anything that blooms in a container, I just use a good potting soil and then mix Color Star in the top 10 inches of the soil before I put the plants in...it is a 19-13-6 with all the other goodies in it, including blood and bone meal...we have only had yesterday and today with sun in over 30 days......take a look at what one day did to petunias....
Wow! That is gorgeous.
There is no intent to discredit Bettygail's beautiful results, but I think we should probably be looking at an increase in soil temperature that made reluctant buds pop on her planting instead of any one brand of fertilizer. I've found very little difference, if any, in the chemical fertilizers I use and the blood/bone meals she mentions are very slow acting in soils and offer no particular benefits that chemical forms of nitrogen and phosphorous don't offer. That said, I would encourage anyone to use products and delivery methods that DO work for them, and Bettygail's got "sumpin good goin' on" with what she's doing, so keep up the good work, Bettygail.
Al
Zone 8b, Southeast, TX Lake Sam Rayburn
Dear Al,
For so long, I have longed to have healthier plants. Now with your detailed description of what a plant needs and how to supply plant needs, I may have a better chance of accomplishing growing healthier plants.
I am most thankful that you took time and effort to share this useable inormation.
I know you do plants well!
Thanking you in advance for my healthier plants, I am
Sudie Goodman, a Happier Gardener
I do thank you Al for providing this very good information. What is your take on adding compost to potting mix? Is it a good way of providing macro-nutrients?
- Brent
Finished compost is not particularly effective at delivering macro-nutrients to plants at optimum rates in container media. Major elements can be found in roughly the following percentages: N - 1 - 2%, P - .5 - .9%, K - .2 - .4%.
Unfinished (immature) compost breaks down quickly in containers. There are also several properties of immature compost use in container soils that can affect plant growth. Immature composts may have high C:N ratios, high soluble salt concentrations, high concentrations of organic acids and several (I think I read 12?) other phytotoxic compounds, high microbial activity, and/or high respiration rates.
For optimum plant vitality, compost you might choose to use in a container medium should always be of highest quality. Please be sure it is mature and stable to avoid plant growth problems. A primary problem with immature compost in containers is that it uses O2 from soils so it will be more likely to have a negative effect on soil oxygen levels.
If you asked the wrong question & really meant to ask about micro-nutrients: compost does supply some micro-nutrients. Type and amounts vary depending on what the compost is made from, but there are many other vehicles aside from compost that deliver micro-nutrients reliably.
I find it easy to leave compost out of my container soils entirely. It is not difficult to reliably supply all essential plant nutrients and grow perfectly healthy plants with either organic or chemical fertilizer/supplements and w/o the use of compost. Besides - it's much more valuable in the garden and beds. ;o)
Al
This message was edited Feb 28, 2007 11:08 PM
Yes, you caught me...I did mean to ask about micro-nutrients but you answered both questions. Over the past several years I have been adopting organic practices for my lawn and gardens. I am a rather inexperienced container gardener but I can see where containers can require a different approach than "in the ground" gardening. Again...Thanks!!
- Brent