I have two videos that go along with this blog article. I wanted to do two videos about fertilizing that would give you some information to best design your own routine. There is no single method for fertilizing your indoor tomato seedlings and transplants. As with any gardening activity.... ask 1000 gardeners and you will get 1000 answers. All different but yet with similar themes.
A plant can not tell the difference between organic and inorganic fertilizer. So use what you prefer and what is available in your area. I don't like the organic products for indoor use. They just smell bad. But fish emulsion and other products will be used in my greenhouse and garden beds. Every product has a use if used with a plan.
The biggest point I want to stress is to use a water soluble fertilizer at 1/2 strength. Some people even use 1/4 strength. Your tomato seedlings and transplants do not need a full strength fertilizer. The plants are small and most liquid fertilizers have a ratio of N-P-K (nitrogen, phosphorous and potassium) that are just to high for plants in seed cells and small cups.
I also want to mention that gardening is a global activity. What we have here in the US in ways of fertilizer choices, convenience and labeling, is not found in every Country. We can only use what we have available to us.
The video shows you the general size of the seedlings for first fertilization. You are waiting for the first set of true leaves to establish. There is a range, because you have to take into account whether or not there was fertilizer in the starting mix. Or does the plant look green and fine or a bit yellow or purple? Sometimes the are signs to fertilizer other times it is just time, because the plant grows to size.
Now the question might be how often to fertilize them after the first feeding. Some gardeners wait until they get outdoors. Some gardeners do a very very diluted strength at each watering. Again it varies. The key is that you do not need full strength.
My practice is about every 10-14 days with 1/2 strength liquid fertilizer until they go outdoors. Sometimes I have used a starting mix that is fertilized. Sometimes my transplant mix is amended with a fertilizer I like (again at 1/2 strength or less). I still stick with my 10-14 day 1/2 strength liquid fertilizer routine. The key is really staying at...yes 1/2 strength or less.
What is the best ratio on NPK for liquid fertilizing? I don't know the exact answer but I prefer something close to 3-6-3 when diluted at 1/2 strength. It took me years to get to that number. I was brainwashed for a long time for higher numbers. I've seen no difference at this ratio compared with something like Miracle Gro Tomato Food which is about 18-18-21. At 1/2 strength it is 9/9/10.5. Either one has worked for me. Less seems just as effective.
Finally as you establish your routine... remember less fertilize is better in the case of tomato seedlings and transplants. You can over do it. It is tempting to give them more of what you think is a good thing. But problems do happen. Have you every salted a tomato or chopped cucumber? What happens? The liquid is drawn out from the tomato and cucumbers by the salt. The higher external concentration of minerals/salt pulls liquid out. The same thing can happen to your plant when there is to much fertilizer around the roots. The roots can get damaged, the plant gets damaged and problems start. I explain that in this video.
Now... all this being said, damaging your plants with fertilizer is very hard but it can happen. Practice a 1/2 strength routine or less and you will be fine. These videos are for information so you can use it to develop and establish your own practice of fertilizing.
Good Luck in Your Gardens,
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