How to Fertilize Tomato Plants, Organically

littletomatoesTomato plants grow with such speed and vigor that it’s easy to be tempted to keep feeding them, thinking that we need to add nutrients for all of that new growth our plant has put on. But the truth is that over-fertilizing tomato plants is just as bad as under-fertilizing them.

Over-fertilized tomatoes develop lots of green growth at the expense of fruit production. And as if that isn’t annoying enough, all of that tender green growth is like a dinner bell for nearby pests and a magnet for disease problems. Under-fertilization results in slow plant growth and poor fruit set, as well as blossom drop and fruit drop.

So, how do you strike the right balance between under- and over-fertilizing your tomatoes? It’s actually pretty simple, and something you only really have to worry about twice during the growing season. (Less work!)

Fertilize at Planting

At planting time, I like to add a bit of compost the the planting hole, as well as several crushed eggshells or bonemeal to fend off blossom end rot. If I have it on hand, I also like to add a bit of granulated organic fertilizer to the soil at this time.

Fertilize at Fruit Set

When you see your first tiny fruits start to form on your plants, it’s time to do the second fertilizer application of the season. This is when I break out the fish emulsion, and give each plant a good, thorough foliar feed, as well as the soil around each plant. This will provide valuable nutrients just when your plants need it most.

Supplemental Feeding

If you find that production seems to be dropping off, or your plants just look “tired,” there’s no harm in giving them another foliar feed with the fish emulsion, or with compost tea or manure tea. This can be done once per month during the growing season to keep the plants growing and producing well.

Good Soil = Good Tomatoes

As with any kind of gardening, success with growing tomatoes starts with the soil. You will want to grow your tomatoes in rich, fertile, well-drained soil with plenty of organic matter. Incorporating compost and composted manure at planting time, as well as mulching with organic mulches such as grass clippings or fall leaves will make a huge difference — and every year, the soil will just keep getting better.

It seems like it’s not enough; that it should be more complicated than that, doesn’t it? But that really is all there is to fertilizing your tomato plants. Most years, we don’t bother doing a supplemental feeding, and, to be honest, we’ve even forgotten to fertilize at fruit set a time or two and everything has turned out fine. One less thing to have to fuss over — always a good thing!

Michigan Gardening To-Do List: July

Here’s a quick list of what needs to get done in your garden in July:

Herb/Vegetable Garden

  • Keep watering and weeding.
  • Harvest regularly to keep plants producing well.
  • Deadhead herbs such as basil regularly to keep them productive.
  • Check plants regularly for signs of pest or diseases.
  • At least once this month, feed your vegetable plants with a foliar feed of fish emulsion.
  • Start figuring out what you want to grow for your fall garden. Either start plants (such as broccoli, brussels sprouts, cabbage, kale, etc.) from seed now, or track down a good source of transplants.


  • Keep deadheading to keep plants looking their best.
  • Water regularly.
  • Fertilize once a week with a diluted (1/4 strength) solution of fish emulsion.
  • You can still sow seeds for many annuals, such as zinnias and marigolds, all through July for fall color as well.


  • Regular maintenance, such as staking and deadheading, will keep your perennials looking their best.
  • If you haven’t mulched your perennial beds already, this is a good time to do so. It will keep weeds down and reduce how much watering you’ll need to do.


  • If you’re growing tall plants, such as dahlias, stake them as needed.
  • If you still have foliage from spring bulbs (tulips, daffodils, etc.) in your garden, you can remove it once it turns brown.

Trees and Shrubs

  • Prune any spring-flowering shrubs this month.
  • Feed your shrubs with a granulated organic fertilizer, or topdress with some good compost.
  • Trees and shrubs will need an inch of water per week to stay healthy, either from rain or from the hose.

Watering Basics

watering_canWhen to water

When your soil is looking dry and the foliage is not looking it’s perky best, it’s time to take a closer look to see if it is time to water. A good way to do this is to poke your finger into the soil near the base of a few of your plants to see if you feel any moisture. If it feels dry down there, it is time to water.

As for the best time of day to water, morning is definitely the prime time. By watering before noon you are giving your plant’s leaves plenty of time to dry out, which goes a long way toward preventing a number of plant diseases.

It’s all about the roots

Focus on the roots (not the foliage) when you are watering your plants. Your goal is to thoroughly soak the root zone of those precious tomatoes, cucumbers, and cone flowers when they need it. For annuals, the root zone is roughly the top 6 inches of soil. For perennials, it is roughly the top 12 inches.

The bottom line

But what if you didn’t notice that your veggies were looking a little limp until later in the day or you’re in a hurry today and don’t have time to let the water soak down a full six inches? Don’t sweat it. Just be careful to keep the foliage as dry as possible (late afternoon is not the time for the overhead sprinkler) and try to give the root zone as good a soak as you can in the time you have available. And maybe plan on running more soaker hose or drip irrigation next year :).