Square Foot Gardening Fertilizer [All about to know]

Every Square Foot Gardener begins with the end in mind: harvesting loads of vegetables from a lush, thriving Square Foot Garden. Will the simple addition of fertilizer make that vision a reality? 

Not always, Square Foot Gardeners say. In small garden spaces, even small additions to soil go a long way. Think twice before augmenting Square Foot Garden soil with fertilizer.

If you started with the prescribed soil mixture for Square Foot Gardens including gardens in planters and raised beds, you may not need any fertilizer.

Also Read: Square Foot Gardening Cantaloupe [Best Tips & Tricks]

What’s a Square Foot Garden? 

Square Foot Gardening was created by the late Mel Bartholomew, who hosted a PBS television series on the subject for eight years.  

Bartholomew’s “Square Foot Gardening” was the best-selling gardening book in history. It puts vegetable gardening within reach of people who don’t have a lot of land or time to garden.

Square Foot Gardening can be done in small yards, raised beds, or planters. And it uses every square inch of space to produce loads of vegetables. 

If you live in a very crowded city like New York or San Francisco, where there isn’t much outside space available, this method is ideal.

His method is based on a raised bed of 4×4 feet divided into 16 squares. You can plant flowers, vegetables, or herbs in these squares. And you should fill them as much as you can.

Depending on what you are planting, you can mix several seeds or plant only one type in each raised bed.

Bartholomew established the Square Foot Gardening Foundation in 1996 intending to end world hunger one Square Foot Garden at a time.  

Square Foot Gardening is popular because it makes organic gardening fun and easy, even for those new to vegetable gardening.

Check Out: Square Foot Gardening Cauliflower

What’s Mel’s Mix? 

Many Square Foot Gardeners say Mel’s Mix is the magic behind Square Foot Gardening. Mel’s Mix is the three-part blend of compost, peat, and vermiculite that makes up the soil for a true Square Foot Garden.

Skipping the step of filling your Square Foot Garden with Mel’s Mix makes for less robust Square Foot Gardening results. 

Each ingredient of Mel’s Mix plays a role in keeping your Square Foot Garden plants healthy. 


Compost is an organic fertilizer for your vegetables or flowers, so it is an essential part of Mel’s Mix. Bartholomew recommended using a blend of five different types of compost in Mel’s Mix.

Since compost makes up a third of Mel’s Mix, you won’t need to add fertilizer to your Square Foot Garden. 


Mel Bartholomew’s soil mix for Square Foot Gardens includes coarse vermiculite, which was his preference. Extra coarse vermiculite is a fine substitute if you can’t find coarse vermiculite.

Medium vermiculite won’t work, though. If you can’t find anything but medium vermiculite, leave this ingredient out and replace it with compost. 

Peat Moss 

Sphagnum peat moss grows slowly and has been overharvested in some areas. Conscientious gardeners looking for a peat moss alternative can substitute coconut coir in Mel’s Mix.

Peat moss helps Mel’s Mix hold moisture but not so much that plants rot.

Have a look: How to Grow Turnips in a Square-Foot Garden

Advantages of Using Mel’s Mix 

This simple soil blend offers Square Foot Gardeners plenty of pluses for taking the time to fill their beds and planters with it.  

Saves Water 

Mel’s Mix retains moisture to make the most of the water you give your garden, but you won’t have drainage issues with it, either. Mel’s Mix doesn’t hold so much water that your plants will have root rot. 

If you live in Jackson, Mississippi, where there are water shortages, this is a good option.

The Right Nutrition 

Because Mel’s Mix includes compost, it nurtures your plants with the right amount of nutrition. You’ll have no need to fertilize. 

Loosely Packed 

Mel’s Mix has a loose texture that lets plants’ roots expand and grow unimpeded. 

No Analysis Required 

When you start your Square Foot Garden with Mel’s Mix, you won’t have to figure out the pH of your soil or what nutrients it lacks. The ingredients of Mel’s Mix have a balanced pH so you’re ready to plant. 

Check: Square Foot Gardening Squash [Most 7 Benefits]

Why You Shouldn’t Fertilize a Square Foot Garden 

Though it is tempting to sprinkle or spray your garden to get bigger and more plentiful vegetables, these reasons not to fertilize your Square Foot Garden should make you reconsider fertilizing. 

Added Fertilizers Change the pH of Your Soil 

If you used Mel’s Mix as the foundation for your Square Foot Garden, then you have pH-balanced, nutrient-rich soil. Adding fertilizer to Mel’s Mix will upset the pH balance of the soil.

Soil with a pH that’s too high or too low can stunt the growth of plants, cause leaves to develop yellow spots or turn brown, or even cause the plants to die.  

Fertilizers Waste Money and Time 

One of the perks of Square Foot Gardening is that it requires very little time and maintenance.

Fertilizing when it’s not needed is a waste of time and money, plus you could be causing damage to the very plants you want to thrive. Leaving plants alone to sink their roots into Mel’s Mix is the best move.  

When You Didn’t Use Mel’s Mix 

Those who are using the soil of the ground where they’ve planted their garden may want to have their soil analyzed to determine acidity and any nutrient deficiencies before adding fertilizer. That way, they’ll know exactly the amendments to add. 

If you set up your Square Foot Garden with dirt in the ground or plain soil instead of Mel’s Mix, you might need to add fertilizer. This is why Mel’s Mix is such a timesaving and money-saving part of Square Foot Gardening.  

If you take the small amount of time and money needed to start your Square Foot Garden with Mel’s Mix, you’ll save money and time in the long run. Regular soil may need amendments to keep plants thriving in your Square Foot Garden. 

When You Are Growing Flowers 

Ornamental Flowers are heavy feeders, so if your Square Foot Garden is filled with ornamental flowers, liberally dilute a fertilizer for flowers and add it to your soil.

Read: Square Foot Gardening Zucchini

Frequently Asked Questions 

You may still have questions about fertilizers and Square Foot Gardening. The answers to these FAQs may give you the information you need.

What is an NPK Ratio? 

You’ll see three sets of numbers on bags of synthetic fertilizer. This NPK ratio refers to the fertilizer’s nitrogen, phosphorus, and potassium content.
An NPK ratio of 15-10-10 means that the product contains 15 percent nitrogen, 10 percent phosphorus, and 10 percent potassium. 

Does Mel’s Mix require fertilizer? 

Because Mel’s Mix is made up of equal parts compost, vermiculite, and peat moss, it already has organic fertilizer in it and does not need additional fertilizer.
If you planted your garden using Mel’s Mix and added fertilizer, you will likely throw your Square Foot Garden’s soil out of pH balance and may cause your plants to be over-fertilized.
This can stunt plants’ growth and may even cause them to die.

How should I fertilize my raised bed garden?

If you have a Square Foot Garden in a raised bed or planter and didn’t start with Mel’s Mix, you may need to fertilize. Even if you used bagged soil with a slow-release fertilizer, watering will wash away some of the nutrients.  
For small raised beds and container gardens, liquid fertilizer may be the best choice. Pick a soluble all-purpose fertilizer with equal parts nitrogen, potassium, and phosphorus.
Follow directions closely since adding too much fertilizer to your raised beds and container plants can stunt their growth. 
The best option, though, is to start your small Square Foot Garden by filling your raised bed or planters with Mel’s Mix. 

How much Mel’s Mix do I need to fill my square foot garden? 

One of the best features of Mel’s Mix is that it is scalable – you can make as much or as little of the Square Foot Garden soil blend as you’d like.
Using an 8-foot-by-8-foot Square Foot Garden that’s 6 inches deep as an example, you need to prepare 32 ft3 of Mel’s Mix. 
The Square Foot Gardening Foundation can help you calculate the amount of Mel’s Mix you’ll need to fill your bed by offering an online calculator

Do different crops need different types of fertilizer? 

Different types of vegetables have varying nutritional needs. Leafy greens require more nitrogen than green beans or peas. Slow growth, stunting, pale leaves, and low yields are a sign your plants need fertilizer.
Soluble fertilizer can be used with younger plants and seedlings in the spring, and older, established plants can be side-dressed with fertilizer as needed.  
Be careful not to apply too much fertilizer, or you will have plants with yellowing leaves. Starting with Mel’s Mix is less expensive, easier, and healthier for plants.  

What is blended compost? 

Mel Bartholomew recommended blended compost for his Mel’s Mix, but what is it? Blended compost for Mel’s Mix has five sources, ideally, but at least three.
These can include manure, kitchen scraps, worm castings, leaves, shredded newspaper, hay or straw, grass clippings, or forest products.  
If you don’t make your own compost, you can buy bagged compost to make Mel’s Mix. Many bagged composts are from a single source, so read the labels and find three different composts to blend and add to your Mel’s Mix. 

What are things to watch when buying compost? 

While plenty of compostable items are organic, not all of them should be in your Square Foot Garden.
Beware of free compost and mulch from city parks and recreation departments as these can be heavy on wood products and could also include weed seeds.  
Look for OMRI or Organic Materials Review Institute on the compost bag label to get the highest quality compost.
Also, don’t buy bagged compost that’s heavy in peat moss since you will already have peat moss as one of the three ingredients of Mel’s Mix. 

Will I need to fertilize Mel’s Mix Next year? 

When you start a Square Foot Garden with freshly made Mel’s Mix, you’ll have fertile soil for that growing season. You may wonder if you need to add fertilizer the next season to get similar results.  
If you work a trowel of compost into Mel’s Mix during and after the growing season and let your Square Foot Garden beds rest over the winter, your Mel’s Mix will have plenty of nutrients for next year.
Some Square Foot Gardeners put dark plastic sheeting over their beds and weigh it down to cover their beds over the winter to let the bed rest, promote composting, and keep any weeds from taking root.

Can Mel’s Mix be reused? 

If you start your Square Foot Garden with Mel’s Mix, you can look forward to a decade or more of harvests.
After you harvested your square, add a trowel of compost, and your Mel’s Mix will last at least 10 years. That gives the used Mel’s Mix a nutrient boost. 
When pulling out plants at the end of the season, shake off any Mel’s Mix that’s clinging to the roots. Soak the plant’s roots in water to remove even more Mel’s Mix, and then use that water in your garden. 
After a few seasons of Square Foot Gardening, you may see the levels of Mel’s Mix decrease. You can fix this by adding in more Mel’s Mix as needed, incorporating it into the older Mel’s Mix.

Square Foot Gardening Fertilizer
Square Foot Gardening Fertilizer

Key Takeaways 

The fertilization motto of Square Foot Gardening could be, “Don’t just do something. Stand there.” 

Having a fertile, thriving garden is the goal of Square Foot Gardening, but that doesn’t always mean adding fertilizer.

You’re better off not fertilizing. If you start your Square Foot Garden with Mel’s Mix as prescribed, then you shouldn’t need to buy or apply fertilizer.

Not only is fertilizer unnecessary, but adding too much of it could harm or kill your plants and limit your harvest. 

Some beginning Square Foot Gardeners may want to rush into planting their garden beds or cutting corners. They’ll use leftover potting soil or dirt from their yards.

But investing in filling beds with Mel’s Mix will save money and time. You won’t need to buy fertilizer if you use Mel’s Mix, and your Square Foot Garden will be healthier and more productive without it.

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