Natural tomato fertilizers come with big promises. Some of them really do feed a tomato plant. Others are mostly kitchen folklore. Here’s how to tell the difference, and how to use the good ones without hurting your plants.
Tomatoes are heavy feeders, according to Virginia Cooperative Extension, and they’re heat-loving plants that need full sun and a long, frost-free season, per University of Minnesota Extension. Feeding them well pays off. Feeding them blindly doesn’t.
Three questions come up again and again:
- What is the ideal natural
tomato fertilizer ? - What is the best
tomato fertilizer ? - Can I use a complete fertilizer on my tomatoes?
The short version: test your soil first, build it with compost, and treat everything else as a targeted fix. A complete fertilizer is fine if your soil test says your tomatoes need it.
The UF/IFAS Gardening Solutions tomato page suggests a 6-8-8 or similar fertilizer, preferably in controlled-release form, while Minnesota Extension says to use a low- or no-phosphorus fertilizer unless a soil test recommends more. Your soil test settles it.
This article covers natural and homemade options, what each one actually does, and which popular claims don’t hold up.
What Are The Nutrients In My Tomato Soil?
To choose the right natural fertilizer, start by finding out what your soil already has. UF/IFAS says all gardeners should submit a soil sample to a licensed lab before adding any nutrients or amendments, and it offers a soil test for home gardeners for a nominal fee.
Virginia Cooperative Extension adds that you can test through your local Extension agent, private labs, or home test kits.
Both routes work, with one caution: Clemson’s Home & Garden Information Center says at-home kits can give inaccurate or inconsistent results, so an accredited lab is the safer bet.
Perform a soil test before you fertilize, and ask for pH too. Minnesota Extension says a pH of 5.5 to 7 is ideal for tomatoes, while UF/IFAS recommends 6.0 to 6.5 for vegetables.
A test also keeps you from adding what you don’t need. UF/IFAS says phosphorus is plentiful in many Florida soils, and Minnesota Extension says many Minnesota soils have enough phosphorus. Nitrogen is the opposite.
In Florida’s sandy soils, UF/IFAS says nitrogen often is the most limiting nutrient and leaches rapidly.
If you’d rather buy than blend, a ready-made organic
Nutrients Needed For Different Stages of Tomato Plant Growth
Once you know your soil, match your feeding to the stages of the tomato plant’s growth cycle.
Nitrogen builds leaves and stems, and too much of it at the wrong time backfires. Minnesota Extension says too much nitrogen leads to plants that are bushy, leafy, and slow to bear fruit, and Virginia Cooperative Extension warns that tomatoes fertilized too heavily may be all vine and no fruit.
Timing matters too. Virginia Cooperative Extension suggests starting to sidedress one to two weeks after the first cluster of tomatoes begins to develop, while Minnesota Extension says to apply fertilizer alongside the row when the first fruits start to enlarge.
You’ll often hear that tomatoes need extra phosphorus at transplanting, usually from bone meal fertilizer. Add it only if your soil test says phosphorus is low. Minnesota
Extension recommends a low- or no-phosphorus fertilizer unless the test calls for more, and Colorado State University Extension says research there found that phosphorus from bone meal is only available to plants in soils with a pH below 7.0.
Potassium is where wood ash from the fireplace comes in. The University of Wisconsin says wood ash can contain up to 5% potassium, and UF/IFAS lists wood ashes among the potassium sources used in organic gardening.
Wood ash also raises soil pH, with about half the acid-neutralizing power of aglime per Wisconsin, so base how much you use on a soil test. It can be a source of potassium for your tomatoes, worked well into the soil.
One warning if you’re trying to hold nitrogen down: blood meal is not a low-nitrogen choice. Colorado State calls it one of the highest non-synthetic sources of nitrogen and says over-applying it can burn plants, and UF/IFAS lists it at 12 to 15% nitrogen.
Now, with that in mind, let’s look at the options.
Natural Tomato Fertilizers And When To Use Them
Natural fertilizers work differently than synthetic ones. Colorado State says the nutrients in organic fertilizers often need soil microorganisms to convert them into forms plants can take up, so release is often slower, and those microbes need soil above 50°F with enough moisture.
Cold or dry soil delays release. UF/IFAS adds that release depends on temperature, soil moisture, and microorganisms, so even the best estimate may not match the actual release rate.
1. Compost
Compost is the foundation. Minnesota Extension says to improve your soil by adding composted manure or other compost in spring or fall, and that you may not need additional fertilizer, depending on how much organic matter you add.
Compost builds soil more than it feeds plants fast. Colorado State notes that compost typically doesn’t meet the legal definition of a fertilizer and adds small amounts of nutrients.
UF/IFAS says nitrogen in compost becomes available more slowly than phosphorus and potassium, and estimates that about 10% of the nitrogen in composted horse manure or vegetable waste is available during the year.
Compost can also supply too much of one nutrient and not enough of another, so testing a compost sample is worthwhile if you use a lot of it.
For timing, UF/IFAS suggests broadcasting finished compost over the garden two to three weeks before planting and working it into the top 6 inches of soil. That is why a simple compost bin pays off over time: you’re building rich soil, not just feeding one season’s tomatoes.
Skip compost tea as a fertilizer. UF/IFAS says compost tea does not provide a measurable amount of nutrition to plants, and adds that tea made with a sugar source can increase the number of pathogens in the tea. University of Illinois Extension says studies show compost tea often has no effect on disease control.
2. Epsom Salt
Epsom salt is magnesium sulfate, and people often sell it as a cure-all for tomatoes. Minnesota Extension says there’s no evidence it makes tomatoes more productive unless your soil is deficient in magnesium, and it should be used only if a soil test shows a deficiency.
Adding it to soil that already has enough magnesium can harm your soil and plants, such as by inhibiting calcium uptake, and spraying it on leaves can cause leaf scorch.
Clemson adds that too much Epsom salt can build up salt around the roots and, because extra magnesium reduces calcium uptake, can worsen blossom end rot.
Blossom end rot is mostly a watering and calcium-movement problem. UF/IFAS Extension Duval County lists three main causes: inconsistent watering, over-application of nitrogen, and soil calcium that isn’t available to the plant, for example because of excess soil magnesium or potassium, dry soil, or root damage.
Its advice is to water consistently, add mulch, get your soil tested, and avoid damaging roots.
Our full guide covers what Epsom salt does and doesn’t do for tomatoes.
Related: Read our article on blossom end rot and Epsom salts.
3. Fish Emulsion
Fish emulsion is a soluble liquid fertilizer made from fish waste that has been heat and acid processed, according to Colorado State.
UF/IFAS lists acid-digested and enzyme-digested fish emulsion at 4-1-1 and says liquid fertilizers made from fish or seaweed can supply nitrogen and micronutrients in the short term when applied to the root zone or leaves.
Follow the label for how much to use and how often. UF/IFAS also suggests feeding seedlings 10 to 14 days after germination with a soluble fertilizer such as liquid fish emulsion or liquid kelp, mixed according to product directions. You can also drench the root zone with fish fertilizer for plants diluted in water.
Fish emulsion is not a blossom end rot fix. UF/IFAS says that if a lack of soil calcium wasn’t the problem, adding more calcium won’t fix it, and consistent watering is the better move.
Related: Tips On Deep Watering Tomatoes
Kelp meal is the other ocean option. Colorado State says kelp is valued not for nitrogen, phosphorus, and potassium but for micronutrients, and UF/IFAS notes kelp meal may have a high salt concentration.
Kelp is often credited with boosting flowering because seaweed extracts contain gibberellin-type growth compounds. Washington State University’s Linda Chalker-Scott reviewed the research and found few, if any, documented advantages to applying seaweed extracts to plant foliage. Treat kelp as a micronutrient supplement, not a bloom booster.
4. Organic Cottonseed Meal
Cottonseed meal is a rich source of nitrogen, according to Colorado State. UF/IFAS lists an average analysis of 7-3-1.5, so check your own bag’s label, since products differ. Because it’s high in nitrogen, use it lightly: too much nitrogen can promote leaf growth at the expense of fruit.
Like other organic fertilizers, the nutrients in cottonseed meal release slowly rather than all at once.
Watch the source. Colorado State says many pesticides are applied to cotton and residues tend to remain in the seeds, and that pesticide-free cottonseed meal is available. UF/IFAS adds that most organic certifiers restrict or prohibit cottonseed meal because of pesticide residues in the seeds. If you buy it, look for a product labeled pesticide-free.
5. Used Coffee Grounds
Used coffee grounds are a modest helper, not a fertilizer. Oregon State University Extension says brewed grounds are close to neutral, around pH 6.5 to 6.8, so they won’t acidify your soil.
They contain 1% to 2% nitrogen and small amounts of other nutrients, but they aren’t a major source of plant nutrition. The main benefit is better soil structure and drainage. Minnesota Extension agrees that modest amounts can be beneficial, but not for lowering pH.
Go light. Oregon State’s soil scientist says people are generally too enthusiastic about coffee grounds, and as the grounds break down, soil microbes temporarily tie up nitrogen.
As a soil amendment, Oregon State recommends working in a half inch of grounds to a depth of 4 inches, and keeping grounds to no more than 20% of a compost pile’s volume.
6. Animal Manure
Animal manure is a classic plant food, and UF/IFAS considers it a great source of nutrients and organic matter. It also comes with rules.
- Never use pig, dog, or cat manure in a vegetable garden. UF/IFAS says they can carry parasites such as roundworms and tapeworms, and the University of Maine gives the same warning.
- Compost it first when you can. UF/IFAS says raw manure can damage plants because of its high salt and nitrogen content and can carry pathogens, so composting fresh manure is always better. Minnesota Extension says not to use fresh manure on tomatoes because it may contain harmful bacteria and increase weed problems.
- If you do use raw manure, follow the 90/120-day rule. UF/IFAS recommends applying it at least 90 days before harvest for crops whose edible part doesn’t touch the soil, and at least 120 days before harvest for crops whose edible part does.
- Mix it into the soil before planting. UF/IFAS says manure generally releases nutrients slowly.
- Chicken manure is the strongest. UF/IFAS lists raw broiler-house poultry manure at 3.6% nitrogen, compared with 0.65% for beef and horse manure, and advises against repeated poultry litter applications on the same spot because phosphorus, copper, and zinc build up.
- Ask about herbicides. UF/IFAS says some herbicide residues can persist in manure, compost, and baled hay, and gardeners should ask about herbicide use history before using any of them.
7. Alfalfa Meal and Seaweed
Alfalfa meal or pellets are often sold as animal feed. Colorado State says they are used mainly to add organic matter, though they also offer nutrients and trace minerals and contain triacontanol, a natural growth stimulant.
UF/IFAS lists an average analysis of 2.5-0.5-2.0. Mulch your tomatoes too: UF/IFAS Gardening Solutions says mulch helps retain moisture and suppress weeds.
Seaweed brings potassium and micronutrients. UF/IFAS lists dried seaweed at 0.7-0.8-5.0 and says kelp meal provides up to 60 trace elements. You’ll also find liquid seaweed fertilizers on the market, which UF/IFAS says can be good sources of nitrogen and micronutrients.
8. Blackstrap Molasses
Blackstrap molasses is popular in homemade recipes, but the research doesn’t back it as a fertilizer. An NC State Extension agent could find no research-based information supporting molasses, in any formulation, as a fertilizer.
Molasses does show up in research for nematode control. A 1980 study in Nematropica found that mixing blackstrap molasses with urea improved control of root-knot nematodes in squash without the plant damage that higher rates of urea alone caused.
A 1997 study in Australasian Plant Pathology found that molasses drenches reduced root galling and nematode reproduction in two pot experiments, and that in a field tomato crop molasses reduced root galling but not root-knot nematode populations in the soil.
Those were pest-control trials, not feeding recommendations, so there is no home fertilizer recipe to take from them.
The Bottom Line
Naturally fertilizing tomatoes works best as a system, not a shopping list. Test your soil, build it with compost or composted manure, add targeted products only where the test shows a need, and water consistently.
Skip what the research doesn’t back: Epsom salt without a magnesium deficiency, compost tea as a fertilizer, and molasses. Use the strong stuff, like blood meal, poultry manure, and cottonseed meal, sparingly, since too much nitrogen gets you leaves instead of tomatoes.
Feeding is only one lever for yield. Next, see how to prune tomato plants for maximum yield.
Frequently Asked Questions
What is the best natural fertilizer for tomatoes?
There isn’t one best product. Extension sources start with a soil test, then build the soil with compost or composted manure, since organic fertilizers release nutrients slowly. Add targeted products only where your test shows a need, and go easy on nitrogen, because too much gives you leafy plants that are slow to bear fruit.
Can I make homemade fertilizer for tomatoes from kitchen items?
Several popular kitchen add-ons do less than their reputation suggests. Oregon State says used coffee grounds are 1% to 2% nitrogen and mainly help soil structure. Minnesota Extension says Epsom salt only helps when a soil test shows low magnesium, and an NC State Extension agent could find no research supporting molasses as a fertilizer. Minnesota Extension recommends compost for improving soil.
Is manure safe to use on tomatoes?
Composted manure is the safer choice. Minnesota Extension says not to use fresh manure on tomatoes because it may contain harmful bacteria and add weeds, and UF/IFAS says never to use pig, dog, or cat manure because of parasites. If you use raw manure, UF/IFAS recommends the 90/120-day rule: apply it at least 90 days before harvest, or 120 days when the edible part touches the soil.
Will Epsom salt or extra calcium stop blossom end rot?
Usually not. UF/IFAS lists three main causes of blossom end rot: inconsistent watering, too much nitrogen, and soil calcium the plant can’t use. Adding calcium won’t help if soil calcium wasn’t the problem. Minnesota Extension says Epsom salt won’t prevent it and extra magnesium can make it worse. Water consistently, mulch, and get your soil tested.
Do tomatoes need a lot of fertilizer?
Tomatoes are heavy feeders, per Virginia Cooperative Extension, but more isn’t better. Too much nitrogen gives bushy, leafy plants that are slow to bear fruit. Start with a soil test and follow the label. Virginia suggests sidedressing one to two weeks after the first cluster of fruit begins to develop.