The Best Fertilizer for Tomatoes at Different Stages of Growth
The best fertilizer for tomato plants contains macronutrients such as Nitrogen, Phosphorous, and Potassium as well as essential micronutrients such as Magnesium, Calcium, Boron, Zinc, etc.
If you're new to gardening, growing tomatoes and picking the best fertilizer may seem like a daunting task. But, don't let that get to you. With the right guidance, you're going to have an amazing crop, year after year. Whether you're growing tomatoes from seeds or planning on buying seedlings from the local nursery, plant nourishment is a topic you don't want to be ignorant about.
But before we proceed, let me get one thing clear. There is no single fertilizer that works best for all gardens. If there were, gardening would be simple and arguably, also outright boring, wouldn't it? Let's take a look at some facts and fertilizer options to help you pick the right ones based on the stage of growth.
Important Facts That You Must Know
- The fertilizer requirement of tomato plants depends on the stage of growth. But it is important that every nutrient be present at all times, the suggested ratio is what changes.
- The roots of tomato plants, in general, aren't deeper than 6-7". I would keep this in mind when mixing fertilizer into the soil.
- Commercial fertilizers have a number series such as 10-8-10 which basically stands for N-P-K. This means the fertilizer contains 10% of nitrogen, 8% of phosphorous and 10% of potassium with the rest being filler material.
- Phosphorous is crucial for the growth and development of roots as well as the fruit and it is, therefore, an important nutrient in the initial stages and then again in the final stage.
- Nitrogen takes care of the foliage, but too much nitrogen leads to bushy plants with little or no fruit.
- Potassium helps the plant grow rapidly and produce flowers and fruit. But it's very important when it comes to photosynthesis and tolerance to some diseases.
Once the tomato seedlings have germinated, they are going to grow very quickly with an initial burst in growth prior to their flowering. As a rule of thumb, it is safe to assume that they would bear fruit within four months of being planted. Of course, this depends on many factors such as the type of tomato plant, the soil, and the environmental conditions.
Tomato seeds do not need any added nutrients to germinate as the seed contains sufficient amounts to put up the first true leaves. If you're planning on planting from seed, you may be interested in my guide on planting tomato seeds to help you get the first stage right. If you are at the stage where your seedlings are ready to be transplanted or if you've got some store-bought plants, you should check out my guide on transplanting tomatoes.
If these steps are not done right, no amount of fertilizer will help. Keep in mind that plants like all life are very resilient and you don't need a pro to get through this stage. But knowing exactly what needs to be done, sure does help.
Ensuring That the Plant Gets to the Nutrients
Before getting into the facts of nutrition, you first need to make sure that your tomato plant would be able to get to the fertilizer you've incorporated into the soil. For this, you're going to need to make sure that your watering techniques lead to deep rooting. The plants aren't just going to be growing in height and girth, but they are also going to branch out, causing them to be top heavy. You may want to provide external support to prevent the plants from drooping and falling over. Deep roots also help in this regard.
Secondly, it is best to place your tomato plant in the garden or a big container, since small containers lead to the clumping of roots, the end result being the plant not having sufficient exposed roots to take up the nutrients it needs.
Fertilizer While Transplanting Tomato Plants
As specified in the list of facts above, phosphorous is vital for the growth of roots while potassium helps with flowering and general growth while nitrogen helps with the foliage.
All plants need nitrogen to grow. Most naturally occurring soil contains sufficient nitrogen for plant growth. But, if you're using a major portion of say coconut husk or some other kind of filler material, you're not going to have enough nitrogen in there.
You would know for sure only if you've tested your soil. However, as a general rule of thumb, if you are using fresh compost, you do not need to add any nitrogen, just phosphorous at the initial stage of growth, that is, soon after transplanting the seedlings. You may not even have to add phosphorous if your compost contained a lot of banana peels and bones.
Bone meal is a great way to stick to organic fertilizers while at the same time ensuring that your tomato plants have sufficient phosphorous to grow strong roots which in turn results in the opportunity to produce a lot of fruit.
Bone meal, as the name suggests is a fertilizer made up of ground animal bones, usually beef bones, but other animal bones including fish bones may be used. Today, most commercial bone meal products available are in the ratio of 3-15-0. One of my favorites is the with a 2-14-0 ratio. The essential micro-nutrient calcium in this mix also prevents blossom end rot, a common tomato plant disease. Jobe's Organic bone meal fertilizer
How to Use Bone Meal?
Before adding bone meal it is advisable that you check the pH level of the soil. If it is above 7, you should work on reducing this before adding the fertilizer. Bone meal is a slow release fertilizer and it takes up to 4 months to completely break down in the soil. This is why one application at the rate of 1 pound to 10 square feet (1 kg to 2 square meters) is all you may need. Notice that I have used the word "may".
It's best to use a combination of bone meal and organic fertilizer spikes, but it's totally understandable if you don't want to use bone meal because it's an animal product. In that case, I would measure my soil and add a bit of traditional phosphorous fertilizer available at your local gardening store or on Amazon.
I would definitely recommend you place 3 to 6 inches away from the stem of your tomato plant just after transplanting. This is even more important if you're growing your tomatoes in a container as the plants use up the nutrients pretty fast. Jobe's 6-18-6 organic fertilizer spikes
You don't have to get yourself Jobe's fertilizers, all you need is a spike that contains a higher percentage of phosphorous and at the same time a decent amount of nitrogen and potassium. Fertilizer spikes just need to be pushed into the soil. Watch the video below for a quick demonstration. In general, they last around 2 months before being used up.
How to Use Fertilizer Spikes
Symbiosis and Organic Tomato Fertilizers
If you are planting in your garden, you may want to consider Organic all-purpose fertilizer. The only reason I'd recommend this is because there are beneficial soil microbes and fungi that help plants grow through a process of symbiosis. Dr. Earths
For example, the fungi Myccorhizal reaches far into the Earth and transports phosphorous to the roots of the plants in exchange for sugar and starch. I first learned about this from Grow It Organically and I'd recommend that you read the page to learn more about other Phosphorous sources.
If you have a well-performing garden, you may already have a high level of activity and symbiotic systems in place and you may not need to artificially induce some into the environment. I'd only recommend you do this if you have a garden that does not get green on its own or if you have added a lot of new inert topsoil.
I Always Suggest Organic Tomato Fertilizers for Two Reasons:
- It's better for the environment and your local water table.
- They are easier to use and are less potent. Inexperienced gardeners that use factory produced concentrated chemical fertilizers (not natural powdered rock) tend to overuse which leads to "lockout", a defense mechanism where the plant completely stops absorbing nutrients due to the high concentration which could negatively affect the plant.
The Growth Phase (Pre - Flowering)
For determinate tomato plants, there is a clear distinction between the growth phase and the fruiting phase. This is not the case with indeterminate kinds. This guide deals with determinate varieties. For indeterminate plants, you're going to need constant fertilization with fertilizers of 8-32-16 or 6-24-24. Basically, the nitrogen content is 1/4 of phosphorous and at least 1/2 that of potassium.
Nitrogen is an essential component during the growth phase of your determinate varieties because it helps form a lot of the structures such as chlorophyll which is essentially the green part of the plant that aids photosynthesis. It also helps aid the formation of genetic material among other things.
If you have good soil and use a lot of compost, you will not have to bother adding any nitrogen. But, if you notice the bottom leaves turning yellow this is a sign that the plant needs more Nitrogen than it is receiving. There are also other causes of yellow leaves, it need not be a Nitrogen deficiency. Not to scare you, but yellow leaves are also an indication of excess Nitrogen, but more often than not it's due to a lack of it.
I personally choose to use compost at the start and then every 2 weeks after the first month I add in some compost tea. This provides sufficient Nitrogen and also replenishes some of the other macro and micronutrients.
Making Compost Tea
Potassium: Just Before Flowering Until the End of the Season
If you want your plant to produce a lot of flowers, it's going to need that constant source of nitrogen, not too much though, because this would only promote the growth of leaves and not flowers. More importantly, this is the time your plant needs some good potassium fertilizer.
I've not really spoken much about Potassium all this while, but it is an important nutrient that helps promote strong growth along with Nitrogen. The only reason I didn't mention it earlier, is because I would be doing it now. If you recall, I did say that your Potassium levels should be at least double that of your Nitrogen if you add fertilizer to your garden. Go ahead and buy yourself some 8-32-16 or 6-24-24 and add it as per the instructions on the pack or you could do what I do, as explained below.
Home Made Potassium Fertilizer and Tea
I collect a few banana peels, chop them up into pieces (an inch or so or circlets as seen in the image below) and bury them in my soil. Some go deep in where I expect the base of my roots to be while some stay up to just an inch below the soil. Banana peels are a great source of this essential nutrient and when you bury the peels, they are a source of slow-release potassium which aids plant growth throughout.
But, that's not enough if you want a lot of flowers. While your plant is growing, keep collecting any banana peels (chop them up) and soak them in a big container, could be an old paint can or even a collection of bottles, but it should be something that you can cover up so that the smell of rot does not spread nor do you want creatures getting attracted to it. Keep adding to this with new banana peel as the season progresses.
Next, find out how many days on average it takes for your specific variety of tomato plant to flower (not fruit). Up to two weeks before this date, start pouring in some of that water you've been collecting. Depending on how much you've got and how concentrated it is, you may have to dilute it or just use a little every other day.
I cannot really give you a deeper explanation on this as this is something you'd figure out from experience. You're going to have to wing it by keeping an eye on your plant. If you notice that growth is slowing down stop adding any more. You can't really go wrong if you keep an eye on the plant.
Onset of the Fruit Until They Are Ripened
During this phase, the plant still needs Nitrogen, but not in large amounts. If your plant has grown well until now, there's no need of especially adding any nitrogen into the soil.
Phosphorous is one of the most crucial nutrients for good fruit. Potassium is also important, so continue adding some of that potassium tea but maybe once a week, not more.
It is important that I state that most garden soil does, in fact, have sufficient phosphorous and by this stage your plant if in a garden would have developed some symbiotic relations that provide it with the necessary phosphorous.
You could always add some if you notice that your fruit is not developing well, this is something you only learn through the experience of the first crop or by testing your soil.
In the first year, there is no harm if you add in some fertilizer that is high in phosphorous. If you choose a fertilizer, maybe go for something on the lines of 8-32-16 at this stage.
Required Micro and Macro Nutrients
Below is a quick summary of the most essential macro and micro-nutrients and a list of some of the important functions they perform. Please note that the list is not exhaustive in any sense.
Continuous growth of foliage.
Root and fruit development and it also helps fight stress.
Continuous growth, aids in photosynthesis and makes the plant less susceptible to some diseases.
For root and leaf growth and helps produce firm tomatoes.
Helps keep the plant green, improves flowering and fruit quality.
Boron and Zinc
Flowering and even ripening of the fruit.
One Size Does Not Fit All
As a conclusion, I need to clearly point out that the guide you've just read covers the growth requirements of tomato plants with a focus on fertilizing general garden soil.
What kind of fertilizer mix you need for your garden depends on the kind of nutrients present and the microenvironment of your tomato bed. You can either learn this from experience or by testing your soil.
Some other points to keep in mind:
- Sandy soil and container gardens would need fertilizers more often than sticky, clay-like soils as sandy soils do not hold nutrients as well.
- Do not let fertilizer onto the leaves of the plant. If you dissolve fertilizer in water, make sure that you water on the ground and not from the top irrespective of the time of day.
Over Fertilization of Tomato Plants
It's common knowledge that a lack of nutrients results in stunted growth, an increased likelihood of disease, no or not the best fruit, etc. But, as already mentioned earlier in this article, excess fertilization is bad and can even be worse than a lack of nutrients in the soil.
Your tomato plant could struggle and grow and produce some tomatoes if the soil is infertile, but it could die due to over fertilization. Do not let this sentence scare you. It's not easy to over fertilize and fixing it is an option, too.
The Common Signs of over Fertilization
- One of the possible causes of yellowing of your tomato leaves could be an excess of Nitrogen in the soil. Under a condition of excess nitrogen, tomato plants do not absorb a sufficient amount of water which results in some of the older leaves yellowing prematurely.
- Excess nitrogen would also lead to a lot of leaves and flowering is put off. Only experienced gardeners who know when to expect blossoms would be able to detect this problem.
- A heavy build-up of sediment and fungi growing on the top surface of the soil.
- Yellowing and wilting of lower leaves. There are so many issues that lead to yellowing leaves, that you need to be an expert to tell the difference.
- A sudden loss of leaves.
Dealing with over Fertilization
- The decay process uses nitrogen, so one way to treat excess nitrogen in the soil is to add mulch or for even quicker results saw dust on to the soil. Mixing in some sawdust and not just placing it on the top would be a better way to use it.
- If you notice fertilizer build up through white salts on the top of the soil, scrape off the top layer and dispose of it.
- Pour a lot of water and let it drain out if in a container or just let it run away or soak into the Earth if it's out in your garden. Do this a few times, it's known as flushing or leeching in case you want to look it up online.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.