What To Put In The Gaps Between Flagstone

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Using flagstone in your hardscape allows you to have the look of natural stone. However, the uneven bits of rock will leave gaps that will need to be filled. And choosing fillers can be a little tricky. Fortunately, with a little whisk of your creative juices, you can easily fill in the blanks. But what are your options? What materials best suit your flagstone hardscape? We did the homework for you, and here's what you need to know.

Depending on what look you're going to do, here are some flagstone gap filler options you can go for:

  • Rocks
  • Sand
  • Plants
  • Mulch
  • Polymeric Sand

Keep reading to know how to put these fillers between the gap on your flagstones, what filler is best for you, and why use fillers in your hardscape.

Flagstone pathway on the garden, What To Put In The Gaps Between Flagstone

What Materials Are Used As Gap Fillers?

The aesthetic you're striving for as well as the types of practical benefits you desire will influence the type of material you choose for your flagstone hardscape.

Here are a few options you can choose from:

1. Rocks

One flagstone filler option is rocks. They can be made up of small stones, gravel, or crushed gravel. They also prevent weed growth and pest infestations, making them a practical and aesthetically beautiful infill choice.

Flagstone patio walkway

Filling in gaps with rocks is the simplest and most cost-effective method. You can level the area between the gaps with sand or soil first, then lay down your rocks before bedding them.

If you want something small and homogeneous, use river rock or pebbles. For bigger gaps, large flagstone chunks work well as filler as well. However, one disadvantage of rocks is that they don't give much color to the patio, leaving it mostly monochrome.

2. Sand

Sand is one of the most common materials used to fill gaps in pavers. The sand granules fill in the gaps between the stones, leaving no empty places. Though a typical filler, if you use sand for flagstone hardscape filler, keep in mind that the sand will erode over time and will need to be reapplied.

A Flagstone Patio shot at an angle fading into a blurred background

Pro tip: To create a unique color for your flagstone patio, mix acrylic and washable paint into the sand first. If you're looking for a beach-themed hardscape, it looks aesthetically pleasing. However, make sure to seal the sand properly after you've filled the holes to prevent moisture from getting trapped beneath them and ruining your flagstone patio.

3. Plants

If you want your flagstone hardscape to have a natural feel to it, you can use plants to cover the gaps in between them!

Flagstone patio with creeping blue star ground cover in bloom between stones

Ground cover plants like moss or turf are a great filler for flagstone patios, and they also give a splash of color to the environment. Turf is best suited to flagstone patios with large, evenly spaced stones.

Another alternative is using wildflowers or small flowers to grow in between the gaps. You can use shrubs like rosemary, thyme, and lavender too!

You just have to keep in mind to trim and water the plants should you try using them as flagstone gap fillers. In addition, you should also consider plants that can thrive in different climates.

4. Mulch

Mulch can also be used to fill up gaps between flagstones. There are mulches designed distinctly to fill gaps, ensuring that your flagstone hardscape looks neat and tidy.

The mulch and soils in this woodland style shade garden are retained with a natural stone curb, and a pathway is created using random flagstone

The mulch's rich, dark color contrasts sharply with the flagstones' neutral tones, providing even another creative aspect to your patio. Weed growth and pest infestation are also reduced using this type of filler.

The crevices between flagstones can be filled with wood bark and mulch. Alternatively, wood chips or several other organic materials like leaves or straw can be used to fill the gaps. Another choice is cocoa shell mulch.

However, if you use wood chips, you must ensure that your flagstone hardscape does not flood frequently, since this could harm the wood chips over time if they become moist.

5. Polymeric Sand

Polymeric sand is generally the greatest filler choice between flagstones, especially for unevenly shaped flagstones. Polymeric sand has been particularly developed to withstand erosion, weed development, and pests on your patio.

This material can be compressed without the use of compacting equipment. This saves a lot of money and time on the project. This is also a great solution for patios because it fills in any gaps.

How To Decide On What Filler To Choose?

Covering gaps or seams in flagstone pavers can be difficult. Depending on your needs, there are a few different approaches to fill the gaps. To help you on this matter, here are five questions you need to ask yourself before deciding what filler to use.

How would you use your flagstone hardscape?

One thing to look into is what will be done with the flagstone area. Depending on how you use your flagstones, make sure the material you choose complements the application or the way your hardscape is utilized.

What method did you use to bed your patio flagstone?

Oftentimes, improper bedding of flagstones can become a problem. So it would be practical and wise to use the right bedding material and prepare it properly. Nobody wants to be strolling on a patio that could collapse at any moment, right?

In addition, proper bedding will make repairs like filling in cracks and gaps should last for many years or even decades.

How much is your budget?

Your budget will also determine the type of material you can use. Are you seeking a quick fix or something that will endure a long time? Depending on the amount you can spare for your hardscape, your filler choice can either be temporary or long-lasting.

What is the size of the gaps?

Another thing to consider is the size of the gaps. Your material should be able to adjunct to the size of the gap. If the gaps are too huge or too close together to form a solid surface, you'll need professional assistance.

Before you decide how to fill up those cracks, talk to a contractor about your options.

Is Your Flagstone Hardscape Prone To Flooding?

If you think your patio will be flooded from time to time or if it frequently floods, you should generally avoid utilizing materials that have been laid out dry such as rocks and wood chips.

How Big Should Flagstones Be Spaced?

In installing flagstones, you don't want them to be too wide apart so that walking along your path feels odd. Any necessary changes should be made before you start laying your flagstones. Place them to your preference around the larger stones in the middle, making sure the spaces between each stone are roughly one inch or two inches.

Final Thoughts

Choosing what material to put in between the gaps of your flagstone hardscape can both be fun and stressful. Aside from a variety of choices, you must also consider some factors to know what filler material suits your hardscape best. If you have more resources to spare, it is much better to ask professionals for their expert opinion. After all, the goal is to have a beautiful and long-lasting flagstone hardscape.

Before you go, if you want to learn more about paver fillers check out these articles:

Can You Use Stone Dust Between Pavers?

How To Choose Paver Joint Compound [What To Consider Including 6 Best Options]

Does Polymeric Sand Prevent Weeds? [Plus Helpful Tips To Stop Weed Growth In Pavers!]