EC, pH and water uptake in hydroponics

Monitoring the interaction of EC, pH and water uptake in hydroponics can prevent most issues and this post explores the interaction with guidelines.

Hydroponic growing

Growing marijuana hydroponically is a method of growing cannabis plants without soil. The plants get fed by soluble fertilizers that are dissolved in water. Hydroponic gardening can be more productive than soil growing, but it is not nearly as forgiving. Soil works as a buffer for nutrients and holds on to them longer than a hydroponic grow medium does. Hydroponic grow mediums contain no nutrients – all the nutrients are supplied via a nutrient solution. Contrary to popular belief, hydroponic gardens often require more care than soil gardens. Because the plants grow faster, there are more things to check and way more things that can go wrong.

The electrical conductivity (EC) and pH of a hydroponic system are vitally important and their interaction is recapped in the next section.

EC and pH

Hydroponic systems are reliant on the composition and formulation of the nutrient solution to supply all the essential elements required for optimal plant growth and yields. However, nutrient solutions are complex and their composition changes as mineral ions are extracted when they flow through the root system. Ideal pH is 5.8 during veg for cannabis and 6.0 during flowering. Best results can be achieved by allowing pH to swing between 5.8 and 6.2.

Deficiencies in hydroponic production are more common than toxicities, as plant uptake of many elements has the potential to strip out nutrients at a rapid rate, particularly from recirculating solutions.

The most common deficiency problems in hydroponic crops are potassium in fruiting plants like tomatoes; iron under certain environmental conditions; nitrogen in some readily growing, highly vegetative crops; and calcium in many species, such as lettuce, tomatoes and peppers.

Deficiencies might or might not be the result of an actual deficiency in the nutrient solution with hydroponics. The problem of overfeeding and nutrient lockout is the main aim of this post, especially on how to prevent it before your plants start showing strange symptoms like the photo below.

nutrient lockout in hydroponics
Nitrogen deficiency in early flower caused by nutrient lockout.

EC, pH and water uptake in hydroponics

Starting with reverse osmosis water can prevent most of the issues when growing with hydroponics. The table below is a reference to assist hydroponic growers to keep the perfect growing environment going.

Water LevelECpHComment
StaticStaticStaticPlant not feeding/drinking, change EC, check meters. Usually, lowering the EC a little (by 0.2) should get the plant feeding again.
StaticStaticRisingpH buffers probably raising pH. This is usual. Having a static water level is not though, a slight reduction in EC (by 0.2) or a res change should resolve this.
StaticStaticFallingUsual cause of this is when media has been rinsed at a lower pH than you require. The other possibility is that too much CO2 has been pumped into the water. Change your res and look at the volume of air pumped plus look at your air source. Res change is recommended.
StaticRisingStaticPlant is leeching nutrients, raise EC by 0.2.
StaticRisingRisingPlant is leeching nutrition, raise EC. An unusual state. The rising pH is probably caused by nutrient leeching back. If these are alkaline, it will lead to the rise in pH. Could also be pH buffers.
StaticRisingFallingAs above. Res change, plus increase in EC.
StaticFallingStaticPlant eating but not drinking. Not ideal. Lower EC by 0.2.
StaticFallingRisingAs above but rising pH is a better sign. Lower EC slightly or res change.
StaticFallingFallingFalling pH along with falling EC but no drop in water level suggests a res change. Depending on other symptoms, lowering EC after res change.
FallingStaticStaticPerfect conditions. EC and pH are at the correct level.
FallingStaticRisingNormal state most people encounter. Nothing to worry about, carry on doing what you are doing unless other symptoms are showing or pH swings by more than 0.5. If pH swings too much, change res and lower EC.
FallingStaticFallingRes change plus a change of EC. Lower EC if over 1.4, raise EC if lower than 1.0
FallingRisingStaticPlant is drinking more than eating, lower EC by 0.2.
FallingRisingRisingPlant is drinking more than eating, lower EC by 0.2.
FallingRisingFallingPlant is drinking more than eating. Lower EC with a res change.
FallingFallingStaticHungry plant, raise EC by 0.1. Very good situation to be in. Nutrient buffers are working and plant is taking a balance of nutrients.
FallingFallingRisingAlmost as above, usually considered almost perfect, raise EC by 0.1.
FallingFallingFallingRes change. Raise EC by 0.2 on new res.

Lastly, a word of wisdom is to always start with half of the recommended dose of nutrients and work up.

References

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