Plant nutrition & Deficiencies

Understanding, reading & reacting to your plants needs can sometimes seem daunting, & when you don't know what's causing a problem, it can be hard to know what action to take. Here are a few pointers that may help: Nutrient availability is directly proportional to pot size, (big pot = more nutrition), I know that sounds obvious but people still over-do it, either feeding a plant that doesn't need it, feeding too much in relation to factors such as plant/pot size, or feeding too frequent. If you have used the correct size pot for the plants stage of growth, and have a good quality horticultural potting soil/mix that has sufficient nutrients, adequate drainage & aeration, then deficiencies should not appear early on unless something else has gone awry. This is where it is important to be able to distinguish between deficiencies where not enough nutrient(s) are being provided & pH lock-out deficiencies where the nutrients are being provided but cannot be "accessed" because of the soils pH becoming imbalanced. This can be caused by the over-zealous use of chemical fertilizers and can lead to a build up of salts in the soil, which cause the pH imbalance, making one or more nutrients unavailable to the plant, causing its deficiency.

A chart showing the optimum pH level needed (6.5) to effectively absorb all of the nutrients.

Click to expand...

In extreme cases this will lead to a multi-nutrient deficiency which then makes diagnosis even harder, as you are dealing with multiple symptoms. If the build up of these salts is severe, the plant will suffer "burn" as it tries to address the high levels of salinity in the soil, through an osmotic response, which draws moisture out of the plant in an attempt to fix the problem, "drying" out your plant, burning its roots and turning its leaves to a crisp. This is why flushing is beneficial if you are suffering from this, to leach out those salts. There are ways of determining what the culprit is, such as testing the soils run-off, to determine its pH level, and then taking the appropriate action, instead of what most inexperienced growers do, which is to assume the plant is suffering a deficiency from scarcity of nutrients & feed it even more, or start applying fixes without addressing the underlying problem. Using a very rich, highly fertilized "hot" soil/mix can also cause problems as they can have far too much nitrogen in them, which can cause burn, & a very high EC (salt) level, & so can still have high salinity levels even if the grower has not started to over-feed their plants with nutrients yet. When watering, water thoroughly until you have run-off, you don't want a lot, as this would be futile & leach out nutrients, you want just enough to know that every part of the medium is sufficiently hydrated. Obviously, you don't have to water like this everyday, just use your best judgement. This becomes easier to gauge as you become accustomed to understanding the amount of water your plants require. This practice is also beneficial as it will allow you to constantly monitor the pH of the soils run-off, & therefore observe the "condition" of your soil. Wet & dry cycles do stress the plants, and exacerbate any issues you may have to do with salt build up. A few millimetres of dry soil on top isn't going to do any damage, but not watering until the soil is coming away from the sides of the container, probably taking days, or even up to a week or more is not a good idea. The reasoning behind why people insist on letting their soil dry out to make the roots "explore" the pot to "seek out" moisture, thereby increasing growth & mass, etc. is not the way to grow strong, healthy roots, and the negative aspects of this practice can far out-weigh any perceived positives; if you have a good quality soil-mix, with adequate provisions for drainage & aeration, then a good watering schedule will not cause root rot, or negatively impact root growth, nor starve them of oxygen or cause any of the other problems people fear unless other factors are at work, such as soil compaction, excessive over-watering, or letting the pots sit in water for too long. And remember that oxygen is supplied to the roots by complex processes & reactions, and is not just derived from the air, because the soil is allowed to dry out.

Are you trying to convince yourself of something? Just trying to figure out the point of this rambling. Which by the way has a few valid points along with the many invalid points.

Sorry you feel that way bud. Care to elaborate on the "many invalid points"?

I guess what I'm trying to say is soil/substrate composition, condition & pH are paramount; soil pH should be constantly monitored & adjustments made as necessary. Adding fresh layers of soil/compost throughout the grow is always beneficial & helps replenish it. Any application of fertilizer with nitrogen in it will over time increase soil acidity, so observing/adjusting the soils pH is crucial. Look after the soil & everything else will fall into place.