Nutrient required by tomotoes during hot & raining day

by Ray
(PJ, Selangor, Malaysia)

Hi Jason, I'm planting tomatoes in my farm using hydroponics in tropical country Malaysia, which is hot (about 24-30c) most of the time. Therefore, what nutrient (N-K-P)? Should I put more during the hot period? Else way, during cloudy and raining days, what nutrients do tomatoes required more? or is it the same??? how about the EC required for hot and raining (cloudy) period.

Beside that, what nutrient do I need to put more if tomatoes start flowing ? P or K ?? or need to lower the N ? Where can I learn how to control the nutrient during the grow of the tomatoes and also the change of the weather?

Answer: Ray- whether cloudy, rainy, or hot, your tomato plants will be fed relatively the same. During the vegetative stage, tomato plants should be given a fertilizer a little higher in Nitrogen, but still containing a good amount of Phosphorus and Potassium. Something like 18-12-12 would work well, for example. For younger tomato plants, 500-700 ppm strength nutrient solution may be appropriate. For more mature plants in the vegetative stage, 800 or 900 ppm may be OK. If you notice any leaf burn, it is a sign that you have reached the upper limit of nutrient strength that you will want to feed to your plants.

When switching to flowering, a fertilizer high in Phosphorus should be used. Something like 12-18-12 or 10-20-10 should be fine, as you still want some Nitrogen and some Potassium in the mix. Nutrient strength will vary a little from one crop variety to the next, but flowering tomato plants should be able to handle 900 ppm nutrient strength. Keep a close eye on your plants for the first sign of leaf tip burn- when you see this, record your current nutrient solution strength. You may also want to back off this number by 50 ppm or so- the feeding program is basically ideal at that moment.

Be sure your fertilizers are complete (contain all secondary and micro-nutrients). Calcium is especially important in growing healthy tomatoes (it transports other nutrients through the plant). One problem I can foresee is high humidity. High humidity prevents tomato plants from transpiring. No (or little) transpiration also means little or no water uptake....which also means little or no nutrient uptake. In this way, high humidity (when ongoing and persistent) can cause symptoms in your tomato plants that mimic a nutrient deficiency. These symptoms include blossom end rot- which flowering tomatoes may exhibit when there is not enough Phosphorus or enough Calcium in the fertilizer.

If you get your nutrient solution strength close to the maximum your plants will tolerate, than this is how you manage your nutrients in relation to the weather: In hot weather, plants will use more water. If they use more water, they will also use more nutrients. If you were already feeding them close to the max, than you come to the following conclusion: During periods of unusually hot weather, you need to mix up your nutrient solution weaker than you would normally mix it up at.

As far as learning how to mix the fertilizer up and use it properly....there are three things you need to pay attention to. One- what your fertilizer mix is made up of (as far as N-P-K ratio). Two- what strength you mix the nutrient solution up at....you will need an EC meter or a TDS meter in order to test and maintain your nutrient solution strength each day. Three- the pH of the nutrient solution. Ideally, the pH of your hydroponic nutrient solution should be between 6.0 and 6.2, which is the pH at which the maximum number of nutrients are available to your plants. To learn a little more about mixing your nutrients and maintaining your nutrient solution properly, be sure to read my how to grow hydro page. Hope this helps you out Ray, and Happy Growing!