Fertilizing Tomato Plants

Fertilizing tomato plants is necessary for optimum growth (both for the plants and the tomatoes). But is there a best way to fertilize? And what about organic fertilizers versus chemical?

Let’s take a look at feeding your tomato plants.

Fertilizing Tomato Plants Organically

Organic fertilizers tend to break down slowly, releasing their nutrients into the soil over time. By “feeding the soil” the plants become stronger and less prone to attack from insects and disease. A good organic approach would be to use a combination of compost, peat, aged manure (or the bagged varieties from the store), and organic amendments such as blood meal and bone meal to create a rich soil.

With this approach, additional fertilizer is usually only necessary only once or twice a season; just after the blossoms appear, and again when a plant is laden with fruit. Good organic fertilizers for this use include fish emulsion, seaweed emulsion, and “manure tea” (fresh manure placed in a large container, filled with water, and allowed to “steep” for about a week). Make sure to dilute any such liquid fertilizer until it is the color of weak tea; even organic fertilizers can “fry” plants if applied too strong!

The organic method of gardening also benefits the environment by not adding chemicals that can upset the balance of nature. We’ve all read about how these chemicals can harm wildlife, not to mention ourselves when they infiltrate the water system. Chemical fertilizers work quickly, but they also leach out of the soil quickly.

Using Chemical Fertilizers

Having made the pitch for the organic method, I realize that not everyone is comfortable using organic methods yet. I do urge you to give the matter some thought, but if you much use chemical fertilizers, here are some general rules:

Fertilizer strength is measured by the percentage of nitrogen, phosphorus and potassium (N-P-K) to inert ingredients. For example, 6-6-6 means there is 6 lbs. of nitrogen, 6 lbs. of phosphorus and 6 lbs. of potassium per 100 lbs of fertilizer. A mixture of 4-12-6 would mean 4 lbs. of nitrogen, 12 of phosphorus and 6 of potassium per 100 lbs.

Look for fertilizers with a higher phosphorus (middle) number. Phosphorus is what fuels the production of flowers, and flowers are how fruits are formed. Try to make it a relatively balanced mix (5-10-5 would be ok, 5-10-8 would be better). You might try Miracle Grow for Roses (you read that right, roses), and use it at 3/4 strength.

Don’t use a “bloom booster” fertilizer with a super-high phosphorus count and really low on nitrogen and potassium.  You might be favoring blooms, but your tomatoes may fail to develop properly later on, because the leaves and roots didn’t get enough of what they need.

Do not use a high nitrogen fertilizer! You’ll be sacrificing fruits for leaf growth!

Do not fall into the trap of thinking “If a little fertilizer is good, more is even better!” Wrong! Too much fertilizer can kill the plants.  It’s much better to use the fertilizer at 1/2 strength and fertilize a little more often.

Organic + Chemical

Yes, you can mix organic and chemical fertilizers, and in fact I often do.  I amend my soil with plenty of compost & manure, then add kelp meal, bone meal and blood meal.  A little fish and/or seaweed emulsion finishes it off.

However, I like to add some of the Miracle Grow for Roses (2/3 strength) at the time the blossoms are starting to open, just to give the plants a little extra “snack”.  I might give a little extra (1/2 strength) if the plants have a heavy tomato load.

That’s what I do — you are free to use whatever fertilizers you’d like, for your own circumstances.

Additional Reading

Now that you’ve learned about fertilizers, you might want to know about tomato insects and tomato diseases. Be prepared!