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DON'T FORGET to FLUSH

tapla (mid-Michigan, USDA z5b-6a)
6 years ago
last modified: 6 years ago

I bet I write instructions that describe how to flush a planting's soil at least once every other day, and probably more often than that. I think it will be much easier to start a thread I can link to than what I've been doing.

For the most part, regular forum contributors and participants are miles ahead of Grower Average, who navigates the growing experience more by feel than faculty. One thing that is poorly understood by Grower Average is the impact that his/her chosen soil has on the ability to keep a plant healthy. An extremely high % off-the-shelf soils hold too much water for extended periods; so much so that root function and root health are negatively impacted by the lack of oxygen that accompanies soggy soil. Root metabolism and water/nutrient uptake is an energy driven process. Plants "burn" food in the presence of oxygen to fuel these processes. Insufficient oxygen levels in the root zone = poor root health = a suffering plant. The plant cannot be healthy unless the roots are healthy.

So, Grower Average often devises a work-around to avoid soil saturation and poor root health. (S)he accomplishes this by watering in small sips - just enough to moisten the soil, but not so much it creates the soggy conditions that sap vitality. The problem with this strategy is, the solution creates a different problem; that being, watering in small sips ensures that ALL of the salts found in tapwater remain in the soil. As the level of salts in the soil solution increases, the plant's ability to take up water and the nutrients dissolved in water decreases. Normally, water moves through cell membranes TOWARD a higher concentration of salts inside of the cell. If the level of salts in the soil solution = the level of salts in the cell, no water moves into the cell. In the case where the level of salts in the soil solution is higher than the level of salts in the cell, water actually moves OUT of the cell. This kills the cell by a process commonly referred to as fertilizer burn. Curing salts actually pull moisture from meats to the surface, where it can evaporate, this is an example in the extreme of how salt affects water movement into and within the plant.

Fertilizer solutions contribute to this issue because all the salts that go unused by the plant also accumulate in the soil, contributing to salt levels. A sister issue to a high level of salts in the soil is a skewed nutrient ratio. Plants do best when the ratio of nutrients in the soil is as close as possible to the ratio at which the plant absorbs the nutrients. When the 2 ratios become divergent, a excess of nutrient A can cause a deficiency of nutrient B; this, while contributing unnecessarily to a higher salt level.

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When it comes to providing a healthy environment for roots, you can see there is plenty of incentive to control soil salt levels and prevent nutrient ratios from becoming skewed. We can easily do this by flushing the soil with some regularity, which is the equivalent of pushing the salt level and nutrient ratio reset button. With an appropriate soil, this can be done with little thought and virtually no worry, every time we water. With soils that simply hold too much water and demand that we water in sips to prevent root health/function issues, we need a plan. Different circumstance sets require different solutions, so be sure to ask. You can find much more about soils if you click me.

To flush the soil of a planting: Water with room temperature water until the soil is completely saturated. Allow the planting to rest for 15 minutes to an hour to allow as much of the salt accumulation as possible to go into solution, then pour a volume of room temp water equal to at least 10X the volume of the pot the plant is in slowly through the soil. This will remove most of any accumulation of offending salts and resolve any skewing of nutrient ratios. It's a good idea, no matter what time of year, to fertilize most plants immediately after flushing the soil. Try to be sure you're using a fertilizer that has a ratio as close as possible to the ratio at which the plant uses nutrients. The NPK % listed on fertilizer packaging is not its ratio. 7-7-7 and 14-14-14 are 1:1:1 ratios. 9-3-6, 12-4-8, and 24-8-16, are all 3:1:3 ratios. Container growers should try very hard to avoid use of fertilizers advertised as 'bloom-boosters', or any number with a middle number (Phosphorous) higher than either the first or third numbers (Nitrogen or Potassium). These fertilizers can badly skew nutrient ratios with even the first application). On average, plants use about 6x as much N as P, so there is NO potential for a positive outcome when supplying many times as much P as the plant requires. I, and a large number of other members, use Dyna-Gro's Foliage Pro 9-3-6. It's designed to closely mimic the uptake ratio of the average plant, and has many other attributes not commonly found in other fertilizers. It also has ALL of the nutrients essential to normal growth. Summarized, it makes fertilizing as easy as it can be, and from 1 container.

The reason for flushing can be traced to the fact you're watering in sips, trying to avoid over-watering; so now that you've over-watered by flushing, what to do? You'll want to get rid of the excess water in the pot. The picture below will supply a visual that should help clarify different methods. Image A represents the soggy layer of soil that refuses to drain from overly water-retentive soils by the force of gravity. Simply put, varying soil properties result in varying heights of the water colume that produces soil saturation. This level is always the same ht for a given soil after the soil has been saturated. Simply by tipping the pot (see B), you can see the level of saturation is the same ht, but the volume of soil that CAN contain saturated soil is greatly diminished.

Figure D represents how reducing the volume of soil in the pot that CAN remain completely saturated, thus reducing the volume of excess water the planting can hold. Adding a wick through a hole in the bottom of the pot where bottom meets side wall can further reduce the amount of water a soil can hold.

If your planting is easy enough to handle, flush the soil over the sink any time you wish. Then, put Newton's First law of Motion to work. In part, it states that an object (the water in the pot) continues to move at a constant velocity (and in the same direction) unless acted upon by a force ..... After flushing the soil, hold the pot in your hand and move it up and down over the sink. You'll immediately see that on the reversal from downward to upward, a measure of water exits the soil, and the sharper the reversal, the greater the volume of water. You can remove all excess water from a pot using this simple trick.

I mentioned ballast above. It's a VERY effective method of eliminating almost 100% of excess water retention if done correctly, and you can find more detailed info here.

Al

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