Tomatoes fruits setting on different sizes & nutrients formula

by Ray
(PJ, Malaysia)

Well, I'm having another problem planting hydroponics tomatoes during the fruiting stage (about 5th cluster flower), I found the tomatoes fruit setting or growing in different sizes at same cluster. For example, the 1st cluster fruit, 1st/2nd fruits are big (about 100mm dia.) while 5th/6th are very small (about 30-40mm dia.). What is the cause on this? is it because of the nutrient or is it normal?

Furthermore , I'm mixing my own fertilizer as following (listing the macro-nutrients only) :-
1) PN (Potassium Nitrate ) - 25 Kg
2) CN (Calcium Nitrate ) - 33 Kg
3) MKP (Mono-Potassium Phosphate) - 8 Kg
4) Mg (magnesium sulfate) - 18 Kg
5) Sop (Potassium sulfate) - 4 Kg

The above contains will mix into the 48 gallon water and about 8 liters of it will be taken to mix with 600 gallon water. (which should be able to get about EC - 2.0) Is this the nutrient formula work well as I use this formula for vegetative and flowering/fruiting stage. (only play around with EC)? I experience it before, working only OK, fruits are small especially fruits after 3-4th cluster.) Should I change it during the flowering/fruiting stage? As you mentioned before, during the flowering/fruiting stage, the Phosphate should be higher, should I add more in MKP ?

Some of the article I went though before, they advice to add calcium / Potassium higher during the fruiting stage, therefore I was wondering what nutrient need more actually? Please advice on the nutrient formula as mentioned above.

Answer: Ray- some tomato varieties tend to set fruit all at once, while other varieties will fruit a little at a time over a longer period of time. It sounds like this is just normal, and you have a variety that behaves in that fashion. As your tomato plants begin to produce fruits, you should adjust the nutrient solution to have high Phosphorus. Decent amounts of Nitrogen and Potassium are still required during this period. It is important the fertilizer also contains a good amount of Calcium, which helps to transport other nutrients within the tissue of the plants. Having Calcium available to the tomato plants as they fruit will help prevent blossom end rot in your tomato crops.

A good N-P-K ratio for the nutrients as you begin fruiting would be 2-4-2, 15-25-15, or 10-25-10 (all of which fit my description above). As far as nutrient strength....the EC of your solution can be slowly increased from young tomato plants to fully mature and fruiting plants. As you slowly increase the EC from week to week, pay close attention to the leaf tips of your plants. At the first sign of leaf tip burn, you should consider this nutrient solution strength to be your "upper limit", and may want to even back down the nutrient strength a little bit.

Looking at your nutrient list, for your flowering/fruiting formula I would recommend using significantly less Potassium Nitrate and (in it's place) use more mono-Potassium Phosphate. This reduces Nitrogen, increases Phosphorus, and still includes a good amount of Potassium and Calcium. This should give you a solid base formula for big tomatoes. I chose to reduce the Potassium Nitrate instead of reducing Calcium Nitrate because Calcium is so important to the healthy fruiting of tomatoes. There is room in the formula to dial back the Magnesium Sulfate a little bit, also.

On very hot days, when the tomatoes use more water, you need to mix the nutrient solution up slightly weaker than you normally would- otherwise, the tomato plants may consume too much fertilizer on hot days. The other option would be to ALWAYS run the EC at slightly less than the maximum. This still produces very good results, and also gives you a little safety "buffer zone" against over-fertilization. Hope this helps you out Ray, and Happy Growing!