Everything you need for mixing MasterBlend

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This article describes how to properly mix MasterBlend and the equipment needed.

MasterBlend, also known as 4-18-38 tomato fertilizer is a very inexpensive and effective hydroponic plant food. It is best combined with Magnesium Sulfate (Epsom Salt) and Calcium Nitrate. Generally, the ratios should be 2 parts MasterBlend, 1 part Epsom Salt, and 2 parts Calcium Nitrate. Basically, use half the amount of Epsom Salt that you would use for the MasterBlend and Calcium Nitrate amounts respectively.  For peppers, I use 2.0 grams/gallon of MasterBlend, 1 gram/gallon Epsom Salt, and 2.0 grams/gallon Calcium Nitrate. I might bump the ratios up to 2.4/1.2 for mature plants. For greens and lettuce, I’ll use 1.6/.8 ratios.

You can source out the materials separately, but I’ve found them on Amazon fairly cheap, all in one package. You absolutely DON’T want the kind that has all three components mixed together in one bag. Get the ones that have them separated.  The reason is they need to be mixed in the proper order. Also, the premixed bags will be inconsistent anyway. The MasterBlend and Epsom Salt could be combined together in the same jug if needed, but I find it easier to mix one thing at a time. You want to always mix the Calcium Nitrate last. This is to prevent a nutrient lockout from occurring. I’ve seen a lot of misinformation online/YouTube showing the Calcium Nitrate mixed second, but this is wrong. The proper order is 1. MasterBlend 2. Epsom Salt 3. Calcium Nitrate.

You’ll need some accurate gram scales to measure the ingredients. I have one that I found on Amazon, AWS brand that weighs up to 600 grams. It’s very inexpensive, I’ve used the same scales for years with no problems. It works with a 500-gram calibration weight, which I also purchased, but I rarely ever need to use it. When I do need to calibrate, it’s only off by about .1 grams.

If you want to mix a gallon, the steps are as follows. Adjust the strength as necessary. If you’re mixing for seedlings I would adjust this by half or quarter. If you’re mixing for a larger container, like a 5-gallon bucket, for example, adjust the amounts up to as needed.

Mixing Process

  1. Fill the container halfway with water. I use tap water, but use whatever you feel is best.
  2. Measure 2 grams of Masterblend and put in the container. Put the lid on and shake it well.
  3. Measure 1 gram of Epsom Salt (Magnesium Sulfate) and put in the container. Put the lid back on and shake.
  4. Add a little more water to the container, filling up to about 2/3 full.
  5. Measure 2 grams of Calcium Nitrate and put in the container. Put the lid back on and shake well.
  6. Top up the container with water.
  7. Check the pH and adjust if necessary to around 6.0 +/-  .2. With my tap water, it comes out close enough, but you might need to adjust yours.
  8. It’s good to check the EC/ppm strength when mixing a new batch. This will give you a point of reference for future batches too. I usually don’t go higher than 2.0 EC for peppers.

Tools Needed

You can also premix concentrates of each ingredient. This saves some time I think. Here’s a video I made showing the process of making premixed concentrates.

Here’s a video I made on the pH meter I use, by Apera Instruments.

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