If you’re attempting to grow an epic garden this summer, you might want to get your hands on some dense, earthy mulch. Whether you’re inspired to bloom some gorgeous wildflowers or aiming to cultivate your own summer veggies, a nutrient-rich mulch mixture is necessity for keeping your outdoor plants happy and healthy all season long.

Mulching your garden beds offers a plenty of benefits, ranging from reducing the amount of water that evaporates from soil (saving you time and money), adding nutrients to your dirt, and keeping weeds and pests at bay, says Angelo Randaci, a master gardener and horticulture expert at Earth’s Ally.

“Mulching is a sound gardening practice,” says Randaci. “But not all types of mulches are good for plants. You’ll be better off using organic mulches because it adds to your soil composition.”

It does require a bit of science to mulch properly and reap all those amazing benefits. Keep reading for Randaci’s tried-and-true tips on how to mulch your garden.

How to much your garden, according to a master gardener

1. The different types of mulch

If you’re not a landscaping professional, brown and black mulch might all look the same. But that’s not the case.

Randaci explains that there are two basic types of mulch: organic and inorganic. Organic mulches are made from organic, or once living, materials, such as chopped leaves, wood chips, shredded bark, or pine needles. All this good stuff is what helps plants and flowers get an added boost of nutrients needed to flourish.

Contrarily, inorganic mulches are made from man-made materials, like rubber, plastic, and other landscaping fabrics. Randaci says that while it won’t amp-up the quality of your soil, an inorganic mulch aids in keeping your garden beds insulated and weed-free. “If you want to improve your soil, use one of the many organic mulches available. As they break down, they’ll enrich your soil,” Randaci says.

Both mulches have their benefits, but do your due diligence—there are some ingredients you should avoid completely.

“Avoid using dyed or rubber mulches. The dye itself is not the problem, but the colored mulches are often made from chipped shipping pallets. Many of these pallets are treated with the toxic insecticide methyl bromide to kill any insects in the wood that is shipped from other countries,” Randaci says. “Only use fresh wood chips as a surface mulch. If using as a soil amendment, allow it to decompose first before incorporating it in with the soil.”

Similarly, steer clear of mulch made from cocoa shells, as they may be toxic to pets, as well as mulch made from cypress, as they’re not usually sustainably sourced.

2. The amount of mulch you need

The second thing to consider is to know how much mulch you need to maximize results. No, you can’t just slap a bag of mulch down and expect your flowers to grow overnight—you have to measure out a precise amount. This will depend on the type of mulch you use, but generally, you want an even spread of 2-4 inches over your beds.

“If using a finer mulch, go with 1/2 inch or less, and apply 2-inches deep,” Randaci suggests. “If you’re using a courser mulch such as pine nuggets, apply 3-4 inches deep.”

Any mulch applied too deeply can affect growth. “It’s good to know how much mulch you need to do an area of your garden,” Randaci says. “Whether buying in bulk or in bags, you can give the garden center the square footage of your area and they will tell you how much you need.”

That being said, you can also take a DIY approach to determine how much mulch you should buy. Here are two simple formulas to use:

For calculating bulk mulch:

We’re going back to high school math. Randaci says to determine the square footage of the area, which is length times the width. Then multiply the square footage by the number of inches of mulch that you want to use and divide that number by 324 to get the cubic yards needed.

So, say your garden bed is 30 feet long and 10 feet wide. The square footage of the bed is 300 square feet. Multiply that number by the inches of mulch that you want to use (in this case 2-inches) and you get 600. 600 divided by 324 = 1.85 cubic yards. You will need 1.85 cubic yards of mulch to cover the 30 x 10-foot area.

For calculating bagged mulch: 

This one’s is a little easier. Randaci says to multiply your square footage following the handy formulas below.

• 1 inch deep: multiply square footage by .083
• 2 inches deep: multiply square footage by .167
• 3 inches deep: multiply square footage by .25
• 4 inches deep: multiply square footage by .33

3. How to spread mulch

In addition to mulch quality and quantity, be strategic with placement. Randaci says to never mulch directly around the stems or trunks of any plant, flower, tree, or shrub. Instead, push your mulch 4-inches away from stems of annuals and perennials, and at least 6-inches from trees and shrubs, to avoid stressing the plant structure.

As for other landscaping no-nos, stay away from using rocks for mulch around foundations for plants like azaleas, hydrangeas, and yews. “These plants prefer an acid soil, and the rock mulch will make the soil more alkaline,” Randaci says. “And avoid straw hay from oats, barley, rice, rye, and wheat. They may contain seeds that will germinate in your garden.”

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