Organic fertilizer for indoors?

Would someone please refer me to a thread addressing organic fertilizer for indoor plants, if there is one?

Or, if anyone has had any experience with such fertilizers, please fill me in. I've found one, but it's basically only worm castings "tea".

Organic fertilizers like fish emulsions and teas tend to increase the likelihood of gnat infestations. Accompanying their use often, is an algal scum at the soil surface that hardens and becomes hydrophobic when it dries, making it difficult to get water to penetrate this layer.

Organic fertilizers rely on the activity of soil organism populations to break them down into elemental compounds that plants can absorb. These populations vary widely with cultural conditions like temp, soil moisture levels, fertility levels, pH ..... so their populations are closer to boom/bust than stable. This makes delivery of nutrients from organic sources erratic or unreliable. Because organic fertilizers tend to remain in soils longer than chemical fertilizers, they have a greater tendency to 'carry-over' from fertilization to fertilization. When this occurs, you may believe you are observing a nutritional deficiency, when actually there are plenty of nutrients in the soil, but no soil organisms to make them available. If you fertilize again, there is the same risk of over-fertilizing that you would with chemical fertilizers; the difference is you may not see the results of over-fertilization until conditions next favor a large soil biotic population. Since you are unlikely to know when populations are high and soil solutions high in total dissolved solids, you probably wouldn't think to attribute it to overly-fertile soil, and might even fertilize again, thinking it might relieve the observable symptoms.

IMO, when measures of the degree of difficulty and the effort:success ratio are taken into consideration, the chemical fertilizers win, hands down. I do, however, respect the fact that there are those who cannot abide by using chemical fertilizers. In the end, it's a personal choice that will be based on a number of factors aside from just results and facility.

Al



This message was edited Feb 20, 2009 7:55 PM

I just want to not worry about salt buildup in the pots as some of my plants are quite large and it would be difficult to flush them out every year. Thanks for your input though. Food for thought.

All the nutrients that plants use are salts, and anything dissolved in water is a solute - like salt, and has the same effect as salt. Even sugar dissolved in soil solution (water in the soil) can cause high levels of TDS (total dissolved solids), EC (electrical conductivity), and fertilizer burn.

The key to keeping a low level of solubles isn't in the fertilizer you use. Tap water can contain high levels of solubles & cause salt-related difficulties, even if you don't apply ANY fertilizers - organic or chemical. A well-aerated, free-draining, and durable soil that you can water copiously at each watering to flush the salts from the soil is the key to preventing salt build-up in soils. Slow (poorly aerated) soils that remain saturated for extended periods invite salt build-up because you must water in small sips to prevent root rot. Salts from fertilizers and irrigation water ALL remain in the soil and accumulate when you must water this way. As salt levels increase, it gets increasingly difficult and finally impossible for water to move into plant cells. In severe cases, the salt levels can become so high it actually reverses osmotic flow of water so it is pulled FROM cells instead of entering them. When there are high salt levels in the soil solution, the plant actually dies of thirst while in a sea of plenty. The solution is in your choice of soils, not the choice of fertilizers.

Al

I have prepared my potting soil pretty closely to your recommendations on other threads, so maybe I won't have the problem with salt buildup as the soils are very free-draining. So you're saying that using even compost tea will not prevent salt buildup if the soil is poor-draining?

I wouldn't look at compost tea as being a fertilizer--it has very low N/P/K levels. Not that it can't be beneficial in the garden for other reasons (helping encourage good microbes, etc) but it is definitely not a substitute for fertilizing.

That's right. Compost tea will not reduce salt accumulation. The only way to reduce salt levels already in the soil is through dilution/removal (out the drain hole). If you are using a well-aerated soil, half the battle is already won. The other half is up to you and watering technique. As long as you remember to flush the soil regularly (every watering is best), salt accumulations should never get to the point they are troublesome - unless you have extremely hard water and fertilize heavily. Frequent fertilizing at low doses and regular flushing the soil keeps nutrient levels high enough to prevent deficiencies and still low enough to facilitate the uptake of water.

Al

I use only rainwater for all of my potted plants indoors and water heavily when needed (runs out the bottom hole). If I fertilize at low doses frequently, I'll have less salt buildup?

I'd not have any plants if I relied on rainwater. It may rain here in April -or not-. :-)

"If I fertilize at low doses frequently, I'll have less salt buildup?"

Well, that depends. Low doses of fertilizer won't do the trick alone. You have to be preventing their accumulation in soils by watering profusely enough to carry a good portion of them from the soil when you water. This also allows you to use a fertilizer that might not have an ideal NPK ratio, and still prevent nutritional deficiencies. The concept is a little complicated, but I'll explain that last part if you're interested.

Here is something I wrote for another forum about watering. You might find it helpful:

* Watering technique is very under-rated in container culture and can easily make the difference between success and failure. To illustrate: When an apprentice goes to Japan to study under a bonsai master, he will often spend 6 months or more doing nothing but learning how to water before he is entrusted with any work on the master's plants.

Ask a greenhouse plantsman what he feels is the most important job in the successful rearing of a crop, and his answer will be "proper watering".

* A generalization - the more often your planting needs water, the healthier the roots will be, as long as you don't forget to water. The need to irrigate frequently indicates good aeration and drainage, which insures that air is returning to the soil before anaerobic conditions cause the death of fine rootage. Watering also forces old, CO2-rich air from the soil and pulls O2 rich air in behind it.

* Don't water on a schedule. Water when the rootzone is first dry to the touch. This can mean watering new plantings (shallow roots) when the lower parts of the container are still wet, but for established plantings, water when the soil at the drain hole feels dry - or use the sharpened dowel trick. Your sense of touch registers 'dry soil' when soils are still about 40% saturated. Plants, however, can still extract water from conifer bark and peat down to about 30% saturation - after that, water is held too tightly for plants to access.

* Your soil should allow you to water at every watering so that water drains freely from the drain hole. The best way to water a container is: Wet the soil until you 'feel' the container is about to start draining from the bottom and stop. Wait 10 minutes and add additional water until about 10-15% of the total volume of water applied in both applications exits the drain hole. The first water allows dissolved solids to dissolve into solution, and the second watering flushes them from the soil.

* If you cannot water as described above w/o risking root rot, your soil is inappropriate. You may be able to correct by adding a wick through the drain hole of the container to remove excess water in the PWT (perched water table) until the planting is mature enough to do it on its own.

Al

Thanks Al. It's pretty clear... I think. I'll see what happens over the next few months.

Mortswife: Luckily, we get lots of rain and melted snow here. I have two rain barrels and one 300 gallon tank that I fill up during the summer, and it lasts me all winter for my indoor plants. I got "hooked" on using only rain water for my houseplants when I first did so with my stubborn orchids, which just sat there for two years after first blooming right from the garden center. Within 6 months of watering them with rain water, they all burst into bloom. Even though I'm on well water, and have a reverse osmosis system for drinking water, I'm convinced that my plants are healthier by using rain water on everything indoors.