Early Garden

Tomato Fertilizer | Fertilizing Garden Tomatoes

Tomato Seedlings | Soil Preparation | Planting in the Garden | Liquid Fertilizer | Tomato Fertilizing Tips

Plants require food just as we do, and just like our diets change in different stages of our growth, so do a plants.  We're going to take a look at feeding your growing tomato plant at different stages of it's life cycle, and take a look at the different kinds of tomato fertilizer you can use to help keep your plants healthy as well as produce the most, best quality fruit.


After your tomatoes germinate, they are getting their nutrition from the seed itself as well as the soil.  But that will be exhausted pretty soon and you'll need to feed the little fellas.  Seeing as how tomatoes should be transplanted to larger containers when they show their first true leaves, what I've always tended to do is water at transplant time with a weak 10-52-10 liquid fertilizer. From this point they get a weak balanced 10-10-10 every week until ready to go into the garden.  Monitor closely though, you want a nice rootball, not a lot of top growth.  Not too much nitrogen, not too often, and get lots of light.

Soil preparation

Now that you have your tomato seedlings started indoors, you can make your way outside as soon as the ground can be worked.  Tomato fertilizing starts before you even get them in the ground!  That's right.  You can do a lot of your tomato fertilizing at the soil preparation stage.  If you have your tomato garden layout done then you can start adding some compost to the soil and work it in as soon as possible.  

I'm a believer in bonemeal as a great tomato fertilizer because tomatoes love phosphorus (the middle number on a fertilizer package). It should be added in the fall before you plant, but if you are a little behind go ahead and throw some in now for a later season release of phosphorous. I used to recommend putting a spoonful of bonemeal in the bottom of each planting hole, after digging really deep and mixing it in a bit, making sure not to contact the root, but I don't do that now.  Primarily because there have been some suggestions about phosphorus overfertilizing leading to leaf chlorosis, a problem that I've had personally. When in doubt, you can't go wrong with a soil test.

You can also add some fertilizer, about 2-3 pounds per 100 square feet of area, which will help carry you through the season.  Remember, that compost has a small amount of nitrogen in it, probably the best form of nitrogen for your plants, but too much nitrogen means green growth but not much fruit.  Therefore, keep the first number low on your fertilizer, like 5-10-10 or 5-20-20.

If you find you aren't able to do this kind of work for some reason, then hang tight.  You can still work some compost in just around the tomato hole at planting time.  Something I've done for years is to dig a big hole where the plant is going to go, probably 1-2 feet wide and as deep as I can get it in my clay soil, probably the depth of a shovel.  Then I make a mound of the removed soil next to the hole for a couple weeks.  This lets the clay soil warm up in the hole around the plant as well as the soil that will be replaced in the hole.  When it comes time to plant, take half of that soil and mix it with compost, and add a teaspoon of bonemeal (if you think you need it), or mix with a small amount of 5-10-10 or 5-20-20 organic fertilizer.

Lastly,  if this seems like to much work, you can skip it all together and opt for one of the prepared water soluble liquid tomato fertilizers that can be applied throughout the season.  Preferably an organic one such as seaweed or fish emulsion because they tend to be more beneficial for the soil.

Planting in the garden

The day you plant out your tomatoes into the garden is a recommended time to fertilize.  Why bother if you've just added all that great compost and fertilizer?  The roots of your tomatoe plant are still tightly nit into a ball no bigger than the container they were potted in, and therefore they have not spread out into that rich soil around the planting hole yet to get that food.  Not only that, they've probably depleted the nutrients from that potting soil they were in.  A liquid fertilizer at this time is perfect because it will give the plant some instant nutrients to assist in coping with transplant stress or shock, and  help those roots grow, so they will venture out away from the plant and be able to draw upon the nutrients in the surrounding soil for the remainder of the season.  Some folks like to water the transplant while still in the container, before it gets transplanted.  I'd tend to agree, not only because you'll save fertilizer and apply it where needed, but also because a moist ball exits the container easier than dry soil.  However, if the surrounding soil in the ground is dry then this water will wick away quickly, or if you water the planting hole afterwards it will leach out of the root ball.  Best bet is to fertilize weakly in the pot, and then again around the planting hole once the transplant is in.  Even if you are reading this a few days after you've transplanted to the garden, there is still time to fertilize by watering at the planting hole directly.

Once they are in the garden, you'll probably want to fertilize tomatoes about once a week for the first month until those roots venture out.  At this point more nitrogen is ok because you don't mind some initial top growth.  I like fish emulsion.  Since you want to grow the roots as well, potassium (3rd number on fertilizer container) is important.  Many state that phosphorus (2nd number on fertilizer label) promotes root growth, but at least one research paper has stated that this is an incorrect assumption that results from a complex situation with nitrogen, manganese and iron, leading to leaf chlorosis.  Because phosphate can overfertilize your crops and nitrogen cannot, play it safe with an organic balanced fertilier at all times, unless you are trying to correct a specific situation to save a plant.

After your plants are established and healthy, you can cut back fertilizing to once every 3-4 weeks, plus at flowering and heavy fruit set times.  Remember to reduce the nitrogen number after plants are established to a fertilizer like 5-10-10.

Liquid Fertilizer

Spraying on a liquid tomato fertilizer from a garden hose sprayer Even if you've done verything else above by preparing your soil and adding amendments, there are 2 times in the season where you would probably want to use a liquid fertilizer anyway, 1) when the fruits begin to bud or flower, and 2) when the fruits have set and the plant is heavy with tomatoes.  Keeping your tomatoes properly fertilized at these times of stress should mean less chance of flowers dropping, greater chance of fruit set, less chance of deformity or disease, and better quality fruit.

Tomato Fertilizing Tips

Plants are picky about feeding.  Too much nitrogen and you get a lot of green but few fruits.  Too little fertilizer and the plant starts to show signs of stress.  You need the right kind of tomato fertilizer at the right time.  The only way I can remember this with all the other gardening activities is to keep a garden journal of when I fertilized last and with what.  You should do the same.  At the time you make that journal entry, write the next scheduled feeding on your calender.

Lastly, recognize that everyone has an opinion or plan when it comes to fertilizing tomatoes.  Remember that your plants will give you signals.  Although there are some general guidelines, you have to remember that tomato fertilizer and the presence of micro-nutrients is a complex balance that isn't easy to understand for the home gardener.  Sometimes a nutrient deficiency can appear in the plant not because of a lack in the soil, but because of the over abundance of another nutrient that is preventing the plant from using it.  That's why most professionals suggest it is best to work at building up your soil over time with organic components like plenty of compost, peat moss or rotted manure.  Practically all of your tomato fertilizer requirements can be made up with just this single step.