Potatoes are easy keepers, in a lot of ways — their bushy foliage thrives just about anywhere. I’ve been surprised more than once by potatoes growing in my very shady compost heap — they sprouted from kitchen waste!
Because they display such happy growth, you might not even think of fertilizing potatoes.
Well, if you want one simple way to optimize your harvest and prevent danger of pest and diseases brewing underneath the soil, it’s fertilizing.
So keep scrolling for super spud-fertilizing tips, including my top 5 favorite fertilizers for potatoes.
| Image | Product | |||
|---|---|---|---|---|
Best Overall Pick  | Best Overall Pick | Osmacote Smart-Release Plant Food Plus
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| View on Amazon |
Best Pick for Micronutrient Boost  | Best Pick for Micronutrient Boost | Neptune's Harvest Fish & Seaweed Fertilizer
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| View on Amazon |
Best Pick for Repeated Feedings  | Best Pick for Repeated Feedings | Fox Farm Grow Big Liquid Concentrate Fertilizer
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| View on Amazon |
Best Organic and Budget Pick  | Best Organic and Budget Pick | Jobe's Organics Bone Meal Plant Food
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| View on Amazon |
Best for Those Who Seek Balance in All Things  | Best for Those Who Seek Balance in All Things | Jack's Classic All-Purpose Water-Soluble Plant Food
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| View on Amazon |
My Overall Top #1 Pick: Osmacote Smart-Release Plant Food Plus Outdoor & Indoor
It’s hard to go wrong with any of these top five fertilizers for potatoes, but Osmacote Smart-Release Plant Food Plus Outdoor & Indoor is my number-one choice for a few reasons.
For one thing, it’s dead-simple to use: You just apply once a season or every 6 months. This is a huge relief for us gardeners used to watering in fertilizers or replacing spikes every couple of weeks.
The 15-9-12 NPK ratio is great for jet-propelling potatoes in your home plot. If you’re thinking far enough ahead, prepare your soil with Osmacote Smart-Release Plant Food Plus Outdoor & Indoor months in advance of potato planting so that, as your potatoes mature, you can supplement with more phosphorus and potassium (P and K) without overfertilizing.
With potatoes, you don’t want the nitrogen levels to outstrip the phosphorus and potassium too much — this would encourage more foliage than spuds. So while Osmacote Smart-Release Plant Food Plus Outdoor & Indoor treads that line of being too rich in nitrogen, it still packs a beneficial punch of your P and K, as well, and you’re going to see nice results in the potato patch.
Osmacote is one of those established brands you’ll see over and over again. Reviewers of this fertilizer often say it was recommended to them by an employee at a nursery or similar plant professional, and that since they’ve followed advice, they wouldn’t buy any other plant food.
This bag will also cover 300 square feet, or pretty much my entire plot, not just the potatoes. I’m happy to pay for it once a year at the beginning of the growing season and save myself the scheduling and mess of subsequent fertilizer applications. This is truly your “set it and forget it” choice!
Top 5 Fertilizers for Potatoes
In a hurry? No worries! Below are my top 5 fertilizers for your potatoes!
- Osmacote Smart-Release Plant Food Plus Outdoor & Indoor (Best Pick)
- Neptune’s Harvest Fish & Seaweed Fertilizer (Best Pick for Micronutrient Boost)
- Fox Farm Grow Big Liquid Concentrate Fertilizer (Best for Varied Feedings)
- Jobe’s Organics Plant Food Bone Meal (Best Organic & Budget Pick)
- Jack’s Classic All Purpose Water Soluble Plant Food (Best for Those Who Seek Balance in All Things)
Why Do You Need a High-Quality Fertilizer For Potatoes?
Like other beautiful and vigorous plants like bougainvillea, potatoes come from South America, and they have the hardiness of a mountain crop to show for it.
As we mentioned, potatoes love to grow — they’ll sprout in a corner of your cupboard or in a cup of water at a preschool! In some ways, they’re the raspberries of vegetables: you buy one to start and you end up with a yardful. So why would you spend money on fertilizer for potatoes?
You might be surprised to learn that potatoes are heavy feeders. Sure, they can sprout from any old spud, but from there they need some serious nutrients to thrive and make it to your dinner table.
How satisfying is it to maximize harvest, to dig up pounds of potatoes at the end of a season to store for months to come? I swear, digging up potatoes end the end of my northern summer is some of the most fun I have gardening.
At that point I’m already looking forward to baked potatoes and lots and lots of savory stew.
Speaking of stew, I really like using vegetable varieties that mature small so I can just wash them and throw them into the pot, with minimal prep.
This includes ball carrots, but also some varieties of fingerling potatoes.
I loved growing one variety of fingerlings called La Ratte (“The Rat”) for its delightful nest of little spuds. Don’t let the name fool you — they were handsome and delicious.
To get high yields, your choice of fertilizer is important. Yes, you can save a few bucks here and there, but there are high-quality picks out there that’ll be worth every penny — after all, in a vegetable garden, this is your food we’re talking about.
We’ll break down the pros and cons of our top fertilizers for potatoes after a look at potato fertilizing basics.
The Basics of Fertilizing
The part of the potato plant we eat is called a tuber, and tubers need a range of nutrients to form well. Fertilizers play an essential role in supplementing soil that might be lacking in certain nutrients.
Rotating crops
A lack of nutrients typically happens when you intensively garden a section of land. This is the reason gardeners and farmers rotate vegetable crops: By switching up the demands on the soil, you’re less likely to deplete it of nutrients.
In my own garden, I always change it up from season to season. My potatoes this year are in the bed I grew sunflowers in last year, for example.
The bed you grew peas or beans in last season is probably your richest bed this year, because peas and beans fix nitrogen into the soil, actively recovering that nutrient level.
The Basic Nutrients for Potatoes
As for potatoes, they need those three basic macronutrients, nitrogen (N), phosphorous (P), and potassium (K), you’ll see printed on fertilizer labels.
Nitrogen promotes the growth of foliage essential for photosynthesis. Phosphorus supplements root growth and that all-important tuber formation. And potassium will help your potato plants thrive, overall, with resistance to disease and good quality tubers.
Calcium is also important for potatoes, both quality and yield. Without it they can develop internal flaws called rust, which you can see in this video. I love the slight Irish lilt of this woman’s voice. Worth it for the soundtrack alone.
Look for our Pro-Tip below for an easy way to provide your potato plants with calcium.
The Best NPK Ratio for Potato Fertilizer
As a general rule, potatoes need a high level of nitrogen in their first weeks of growth. Our top-pick fertilizer will provide great general growing conditions in a very hands-off way, but if you want to be more involved, you can switch up fertilizers while your potatoes are growing.
To do this, select a fertilizer as high as NPK 34-0-0 for these heavy feeders. Use this as directed until month two of potato growth.
From two months on until two weeks before harvest, specifically supplement your phosphorus and potassium soil levels. A fertilizer formula like 12-12-17 or 14-7-21 will boost your potatoes right up onto the cutting board.
How to Tell When Your Potatoes Need Fertilizer
It’s always good to test your soil before growing a darn thing. You can find basic home test kits at garden centers or online, or, for a more extensive analysis, ask your local agricultural extension.
Here’s a handy break-down of reading soil-test results.
Testing your soil will guide your first fertilizer choice. You might need to specifically augment phosphorus or calcium for the good of your potato tubers, for example.
But even if your soil-test results are pretty good, you’ll probably want to keep it robust as your put new demands on it growing vegetables.
My first community-garden plot was on former Shaker farmland that hadn’t been planted in decades. It had basically been sitting and enriching with a cover crop. It was wholly organic, chocolatey rich, loose, lovely stuff, and yet the expert garden directors STILL recommended applying fertilizer.
When you have a good thing, keep it good!
Visual signs your potatoes need fertilizer in your plot include weak foliage growth and yellow or spotted foliage, common signs of nutrient deficiency. Solve these fast with our top picks for fertilizers for potatoes.
Signs of potassium deficiency in potatoes include hollow centers. Unfortunately, once you see these signs, it’s typically too late to replace potassium and safeguard your yield of potatoes. Be sure your fertilizer contains potassium before it gets to this point.
When Is The Best Time To Fertilize Potatoes?
For potatoes, you can choose a fertilizer to apply regularly, as frequently as every one-two weeks from the time of planting. This first fertilizer should have a high nitrogen content. Use it consistently until your potato plants are about 2 months of age.
Then, switch to a fertilizer with a higher phosphorus and potassium content. Use this as directed until two weeks before you plant to harvest. (As a general rule, you should stop fertilizing two weeks before harvest so you’re not ingesting fertilizer!)
Can You Overfertilize Potatoes?
Yes, it’s possible to overfertilize potatoes. In particular, guard against applying too much nitrogen around bloom time — this can actually completely inhibit tuber growth.
Other than that general rule, watch for signs of overfertilizing such as yellowing leaves, brown leaves (which can be a sign of fertilizer burning), and a crust on the soil that signals excess fertilizer.
What to Consider When Choosing The Right Fertilizer For Potatoes
One fall day I went to the compost heap in the corner of my yard and found a surprise: 18″ tall potato plants growing in full shade. They’d sprouted from old, wrinkled, grocery-store potatoes I’d tossed in weeks ago, despite the cooling outdoor temperatures.
Evidently, if you give potatoes enough of the right nutrients, they’ll grow almost anywhere. You might assume that because potatoes grow underground, you can treat them like a root vegetable, but potato-plant needs are a little different, here.
You could grow potatoes on pure compost like that, but sometimes you want a little more control of the nutrients you’re adding to the soil to guarantee a result. Sometimes you don’t have enough kitchen compost for the whole patch. So how do you go about selecting a commercial fertilizer?
Soil Testing and Soil pH for Growing Potatoes
Most soil tests will give you a read-out of nutrients, content of organic matter, and a pH level.
Potatoes like soil on the acidic side, between 5.0 and 6.0.
If your soil pH is higher than that, look for sulfur or peat moss additives, or try adding used coffee grounds or even pine needles to the potato bed.
If your potato patch is too acidic, try adding agricultural lime to adjust the pH up.
If your soil is poor in the major macronutrients of nitrogen, phosphorus, and potassium, you’ll see weak growth, stunted growth, and leaves discolored (often yellow).
This means for growing potatoes you’ll need the help of good-quality fertilizer with a balanced NPK ratio, especially one that’s not to heavy on the nitrogen (N) and has a good shot of phosphorus (P) and potassium (K).
In addition to those macronutrients, you’re going to want to ensure your soil has some micronutrients essential for growing potatoes, such as calcium, which is particularly important for tuber health, but also magnesium.
Then there are some trace nutrients you’ll want present in your soil, like boron, copper, and zinc.
How to Gauge Fertilizer Quality
It pays to read labels with fertilizer, too. Some fertilizers will be certified organic by major organizations — you can be sure these have a high level of quality and don’t contain pesticides.
You can also look into specific brands and sources. Our local garden-center employees often recommend products, even ones they don’t carry in their limited space. I’ve also received hot tips from community-garden organizers — in general, gardeners love to geek out about growing plants. Don’t be shy to ask!
How Much Fertilizer Do I Need for Potatoes?
This depends wholly on your own soil’s specific nutrient levels, on your goals for your crop, and on the fertilizer’s content. Use a soil test to get started — some tests will provide recommendations for applying fertilizer. Going to your local agricultural extension is always a good bet.
Slow-Release Fertilizers for Potatoes
This type of additive releases its nutrients over the course of months. It generally comes in granular form.
Slow-release fertilizer can provide a steady supply of nutrients for potatoes. They also leach less, meaning you waste less product, and don’t need frequent reapplication.
That said, be careful not to overfertilize potatoes, especially with nitrogen, which would leave you with bushy green growth but shrunken tubers.
Quick-Release Fertilizers for Potatoes
These fertilizers offer potato plants an immediate boost, which can be handy when you want to promote tuber growth with phosphorus and potassium.
They are also great for adjusting nutrient deficiencies during the early stages of potato growth.
That being said, you might find it unwieldy to come up with a fertilization schedule — some recommend reapplication every week or two. It can get tiresome and messy, not to mention expensive.
Urea Fertilizer
Urea is a common source of nitrogen. While it sounds a little gross, like bone or blood meal, it’s been cleaned and processed until its original form is almost unrecognizable. And, hey, we’re dealing with soil here — things get natural.
Urea is a great source of a vital nutrient for potatoes. Lots of fertilizers will list it as the first ingredient. But be careful you don’t overuse it in the potato patch. If you do, you’ll wind up with a lovely green potato bush that has no tubers to speak of.
Organic vs. Non-Organic Fertilizer for Potatoes
Organic fertilizers are derived from natural sources. This often means compost, manure, or fish emulsion. They provide slow-release nutrients and improve soil structure and general health.
Non-organic fertilizers are typically mineral-based. These provide readily available nutrients.
When it comes to deciding between them, it’s typically sheer preference and gardening philosophy, as well as the specific needs of your soil and potatoes.
It also can come down to convenience vs. cost. I’ve trucked in loads of aged horse manure for a fraction of the cost of store-bought fertilizer, but it took most of a day to procure it and work it into my garden (and I’m only working 400 square feet of area).
Sometimes it’s nice to just open a bag and pour it on. It depends on your resources of time as well as money!
My Reviews of the Best Fertilizers for Potatoes
1. Osmacote Smart-Release Plant Food Plus Outdoor & Indoor (Best Overall Pick)
Osmacote is a widely loved brand. Users swear by it for everything from vegetables to houseplants.
It boasts a 19-6-12 NPK ratio, a fairly balanced nutrient composition with a concentration of nitrogen that will promote healthy growth and development in potatoes, while also offering phosphorus and potassium for robust tubers.
The smart-release granules ensure a controlled and gradual release of nutrients over time, providing easy, steady nourishment to your potato patch.
| PROS (+) | CONS (-) |
| + Good for starting potatoes + Higher nitrogen content for robust growth + Won’t burn plants | – Can’t adjust feedings on the fly |
2. Neptune’s Harvest Fish & Seaweed Fertilizer (Best Pick for Micronutrient Boost)
This fertilizer contains a blend of seaweed, humic acid, and nutrients designed to nourish plants down to the micronutrient level.
The 2-3-1 NPK formula will boost potato plants’ growth at all levels.
Organic and natural and derived from sustainable sources, this is an environmentally friendly choice.
Fish fertilizer can stink to high heaven, however, and you’ll have to apply it pretty often.
| PROS (+) | CONS (-) |
| + Organic, natural, and sustainable + Micronutrient-rich + Stimulates overall growth, down to the tubers | – Frequency and smell of application |
3. Fox Farm Grow Big Liquid Concentrate Fertilizer (Best for Repeated Feedings)
With an NPK ratio of 6-4-4, this fertilizer will deliver a powerful boost of nutrients potato plants need for a successful harvest.
It’s natural and organic, meaning it’ll also enhance soil health, promote microbial activity, and improve nutrient take-up.
You can also dose it effectively as you progress through the season.
That said, liquid fertilizers generally require more frequent application, which is tricky here, since you’ll need to watch you don’t overdo it on nitrogen and risk dwarfing your tubers.
| PROS (+) | CONS (-) |
| + Powerful formula + Easy application with regular waterings + Organic and natural | – A bit pricey compared to other picks |
4. Jobe’s Organics Bone Meal Plant Food (Best Organic and Budget Pick)
This fertilizer packs a wallop of phosphorus, which is essential for good tuber development in potatoes.
All-natural, organic, and good for soil, it’s also a good price-point for a formula that will last most gardeners all season.
That said, it’s not for vegetarians/vegans as it contains mostly animal byproducts. You also might need to supplement nitrogen for potatoes, particularly at the beginning of their growth and depending on your soil.
| PROS (+) | CONS (-) |
| + All-natural, soil-building + Good value + Registered organic | – Animal byproducts |
5. Jack’s Classic All Purpose Water Soluble Plant Food (Best for Those Who Seek Balance in All Things)
This NPK 20-20-20 formula is somewhat of a dark horse, but, hey, if you’re looking for a balanced blend, here it is!
Your potatoes will get their macronutrients and some essential micronutrients, to boot.
Reviewers love this easy-to-use fertilizer, and a 1.5-gallon tub of it goes a long way, at one tablespoon per gallon of water.
Not at the top of the list simply because I’d prefer a little more phosphorus and potassium for potatoes.
| PROS (+) | CONS (-) |
| + Packed full of macro- and micronutrients + Easy-to-use and the convenience of a resealable tub + Will feed plots for months | – Might need more P and K for potatoes |
My Top Pick: Osmacote Smart-Release Plant Food Plus Outdoor & Indoor
Gardeners often find Osmacote when a nursery employee recommends it for vegetables. They use it for this trusted recommendation and never go back.
With a 19-6-12 NPK ratio, this fertilizer has a fairly balanced nutrient composition. Your spuds will receive plenty of nitrogen to promote healthy growth and development from root to leaf, but they’ll also get the phosphorus and potassium crucial for healthy, tasty potatoes.
The smart-release granules ensure a controlled and gradual release of nutrients over time, providing easy, steady nourishment to your potato patch.
Get this fertilizer in your soil early in the season so your potatoes will benefit from its nutrients throughout their growth. It’s our winner for potato dinner!
Final Thoughts
Potatoes are some of the easiest and most rewarding garden vegetables to grow. Who doesn’t like a baked spud, some creamy mash, crispy fries, or a hearty stew? And it’s even more satisfying when you know it came from your own ground.
You might be surprised how fertilizing can augment the health of your potatoes and increase yields. I hope you pick one of my picks for best fertilizers for potatoes and enjoy a great harvest.
And if you’d like to try saving a couple potatoes for seeding your crop next season, take note of these long-storing varieties!