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The Best Seed Starting Fertilizers

Seedlings require little added nutrients at the beginning. But, they can benefit from seed starting fertilizer once they develop true leaves. These are the second set of leaves that appear on a seedling after germination.

So, which fertilizers are safe to use? And when should you fertilize seedlings?

In this post, I’ll go over the four best seed starting fertilizers and tips on fertilizing. Keep reading for more!

Cucumber seedlings with true leaves are ready for seed starting fertilizer.
True leaves growing on cucumber seedlings.

Our Top Picks

Best Overall:
ArgoThrive Fruit and Flower Organic Fertilizer

Optimum NPK Ratio:
Dr. Earth Pure Gold All Purpose Plant Food

Best Overall

ArgoThrive Fruit and Flower Organic Fertilizer

AgroThrive Fruit and Flower Organic Liquid Fertilizer - 3-3-5 NPK (ATFF1032) (32 oz) for Fruits, Flowers, Vegetables, Greenhouses and Herbs

My top pick for the best seed starting fertilizer is ArgoThrive’s Fruit and Flower Fertilizer. This liquid fertilizer has an NPK ratio of 3-3-5, which is great for young seedlings.

The organic fertilizer’s ingredients are made from fermented fish and grain by-products. The fertilizer is already digested, meaning it’s fast-acting. You’ll most likely see impacted growth within one week of application.

Simply mix two ounces of the liquid with a gallon of water, and apply it to seedlings weekly.

This fertilizer comes with 32 ounces of solution, so it goes a long way over the season. For $27, this is a pretty good deal.


  • Organic
  • A little goes a long way
  • Low dose NPK ratio
  • Fast-acting


  • Can have a fishy smell
  • Pricier than other liquid fertilizers

Best NPK Ratio

Dr. Earth Pure Gold All Purpose Plant Food

Dr. Earth Pure Gold All Purpose Liquid Plant Food 24 oz Concentrate

Dr. Earth’s Pure Gold All Purpose Plant Food has the best NPK ratio for seedlings. At 1-1-1, you’re almost guaranteed not to overwhelm your seedlings.

The fertilizer is derived from composted food products, and it’s OMRI organic.

Dr. Earth’s Pure Gold is a liquid fertilizer that only needs to be applied every 14-28 days. Mix four ounces of fertilizer with a gallon of water to dilute and apply Pure Gold.

Even though it is a low dose, many reviewers rave about the good results they received from this seedling fertilizer.

This fertilizer is also pet-safe, so you can rest assured if you have any four-legged family members.


  • Low-dose NPK ratio
  • Organic
  • Made in the U.S.A.
  • Pet-safe


  • None

Burpee All Purpose Granular Plant Food

Burpee Natural Purpose Granular 4-Lb Organic Food for Growing Strong Plants | Good for Vegetable Garden, Flower Garden & Seed Starting, 4 lb, 4lb. Bag

Burpee’s All-Purpose Granular Plant Food is made to be mixed into your seed starting mix. The NPK ratio of 4-4-4 will slowly deliver a healthy amount of nutrients to your seedlings.

Besides nitrogen, phosphorus, and potassium, this fertilizer contains calcium, magnesium, sulfur, and iron to aid with growth.

The fertilizer is derived from poultry litter and feather meal, and it’s certified organic by OMRI (Organic Materials Review Institute).

Since the fertilizer should be combined with your seed starting mix, I recommend waiting until you pot up your seedlings. Once seedlings move to a four-inch pot, they will be able to handle added nutrients better.


  • Cost-friendly
  • Organic
  • Contains more added nutrients


  • Need to wait until seedlings are potted up to apply

Neptune’s Harvest Fish Fertilizer

Neptune's Harvest Fish Fertilizer 2-4-1, 18 Ounce

Neptune’s Harvest Fish Fertilizer is the best seed starting fertilizer if you like using a fish emulsion.

Fish fertilizers are made from fish by-products and are a great, natural source of nutrients. They are less likely to burn plants and are an eco-friendly addition to soil and seed starting mix.

Neptune’s NPK ratio of 2-4-1 is perfect not to overwhelm seedlings. This liquid fertilizer is applied a teaspoon at a time, so you’re not applying a large amount to your seedlings.

The fertilizer only has to be applied every 2-3 weeks, so your bottle of fish fertilizer will last a good while.

It’s a cost-friendly alternative to other liquid fertilizers. And the simple ingredients are perfect for organic gardeners.


  • Cost-friendly
  • Low-dose NPK ratio
  • Organic
  • A little goes a long way


  • Can have a fishy smell

What Should Be in Seed Starting Fertilizer

Fertilizer granules.

The most important thing is finding a seed starting fertilizer with a low, balanced NPK ratio. The NPK ratio reflects how much nitrogen, phosphorus, and potassium are in a fertilizer.

Nitrogen helps with foliage development, while phosphorus and potassium aid in strong root, stem, and fruit development.

An all-purpose fertilizer works great. But, the ratio numbers shouldn’t exceed four or five (4-4-4 or 5-5-5). You can often get away with fertilizers that contain even less than that.

If you use a higher dose of fertilizer, you will often overwhelm and kill your seedlings. It’s best to wait until plants are established in the garden to use those large ratio fertilizers.

Tips on Fertilizing Seedlings

A starter tray of marigolds with true leaves.

When to Fertilize

Knowing when to apply seed starting fertilizer is pertinent. Apply it too early, and you may stunt your seedlings’ growth altogether.

Seed starting fertilizer should be applied after seedlings have established healthy, true leaves. Before that point, they can grow without any added nutrients.

After seedlings develop true leaves, they will focus more on foliage development. Added nutrients can be helpful to aid in this process.

Oftentimes, you can wait until you move your seedlings into a larger pot. At this point, they will be developing a larger root system as well.

When Not to Fertilize

An unhealthy tomato seedling.

You may be tempted to fertilize your seedlings if they appear unhealthy. It’s easy to assume they don’t have the nutrients they need. But, there is often another simple solution during this stage of growth.

For example, leggy seedlings are usually not receiving enough light. You should move the grow light closer to your seedlings, or invest in a brighter grow light.

If seedlings are wilting, they are usually either over or under-watered. The best way to determine this is to feel the soil surrounding the seedlings. If they are waterlogged, ensure you’re providing holes for drainage and airflow.

Frequently Asked Questions

Watering seedlings.

Is it better to use granular or liquid fertilizer?

Seedling fertilizers are typically either granular or liquid. Both are useful in different ways.

Most of the time, I recommend using a liquid fertilizer because of its convenience. These can be easily applied to seedlings without transplanting them. The downside is that liquid fertilizer requires frequent applications.

Granular fertilizer has to be mixed into the soil. So, if you don’t pot your seedlings up, you’d be applying fertilizer before your seedlings even germinate.

But, granular fertilizers release slower, so they have to be applied less often. And the slow release is good for seedlings.

Do I have to fertilize my seedlings?

No, it’s not technically required to fertilize seedlings. At this young stage, seedlings can produce healthy growth without any help.

That’s why good seed starting mixes don’t contain any kind of added food or fertilizers.

But, as seedlings near time to transplant, added nutrients can give them a jumpstart before being moved to the garden.

Wrapping Up Seed Starting Fertilizer

A starter tray of broccoli seedlings.

Try out one of these seed starting fertilizers to help your seedlings produce healthy foliage. My top pick for the best seedling fertilizer is ArgoThrive Fruit and Flower Organic Fertilizer. With its low, balanced NPK ratio and organic ingredients, it’s a good addition to your seed starting routine.

Learn all there is to know about seed starting. Visit our Seed Starting Page for tips on starting your favorite vegetables. We’ll even give you the best products to accomplish it!