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Amendment math to help get your soil in tip top shape

ALBUQUERQUE, N.M. — Q. How can I figure out how much, what you call amendments, do I add to my garden soil? – D.U., Albuquerque

A. It can seem daunting to try and figure out how much extra “stuff” to add to your soil to create an area where you can garden successfully.

I’ll keep it very simple.Tracey Fitzgibbon

First know what you’re thinking of adding. Manure from herbivores (plant eaters) is one of the most common soil amendments there is. Then there is topsoil. It’s usually a mixture of sand, milled compost, and sometimes vermiculite, perlite and some manure. Compost is usually a product containing all sorts of plant by-products that have been piled up, watered and allowed to decompose to a certain extent. It is milled to break it up into small pieces that are easily worked into the ground. Some bagged composts are plant specific – like cotton burr compost – and it’s nice “stuff” to add to your gardens.

Peat moss is a good amendment too, although it doesn’t add a lot of nutrition so to speak. Its main job would be to assist the soil with water holding capabilities. Peat moss can also help adjust the pH value of the soil, helping make our naturally alkaline soils lean to a more plant-friendly acid level. In these parts, more is better since it’s difficult to get much to grow unless you add extras.

Now, how much will cover what? Since most soil amendments are sold in cubic foot bags it’s time to think visually. Imagine a box, 12 inches by 12 inches by 12 inches. The space in that box equals one cubic foot. Slice the box into 1-inch slabs (imagine tiles) and you’d be able to cover 12-square-feet of space. Remember this is just a visual lesson, I don’t expect you to go out and fill boxes and cut into slabs!

If you spread that one cubic foot of amendment over a 12-square-foot area (or a 3-foot by 4-foot space), then turn it in, you’re not going to see much evidence that you added anything. Your existing soil will take it in, rejoice with the addition, but still be mostly native soil.

So the more you add, the healthier your soil becomes. In order to calculate the base amount of amendments you’ll want to start with you need to measure the space length by width. Say your area is 6 feet by 8 feet. Six feet by 8 feet equals 48 square feet. Divide by 12 – remembering each cubic foot bag can cover a 12 square foot area at an inch thick – and you get four. So, in order to cover that 48 square foot area with an inch of amendment, you’d need four 1 cubic foot bags.

But remember the more you invest in the soil, whatever you plant in it will be much better off!

Q. I’ve done so well attracting hummingbirds to my feeder that I’d like to plant some flowers for them. Any suggestions? – E.H., Albuquerque

A. How fun! There are lots of plants, shrubs, vines and plants – both perennial and annuals – you could add to your landscaping to offer these jewels a more varied diet. Hummingbirds are specialized feeders, so look for plants that wear tubular shaped blooms. In the perennial world any p enstemon plant would work. Digitalis (foxglove) and n icotiana would attract. A clumping red hot poker ( k niphofia ) or their namesake plant, hummingbird plant (zauschneria) will delight you both! In the hyssop family, a plant called Agastache or hummingbird mint is an absolute charmer!

Not only do you get truly nifty flowers, but the foliage gives off the most wonderful scent when it’s bruised or bumped up against. If you’re into hanging baskets, one filled with fuchsia would be a treat for you both. If you have a bit of space, honeysuckle or trumpet vine would be a good addition. Just know that without proper containment, both have the ability to overtake space. With space to offer consider the Hesperaloe parviflora or red tip yucca.

Do some research as to how much room you want to dedicate for your hummingbirds, make note of how much sun the spaces will get and do a bit more homework. There are lots of plants that can offer hummingbirds a varied diet!

Happy Diggin’ In!

Tracey Fitzgibbon is a certified nurseryman. Send garden-related questions to Digging In, Albuquerque Journal, 7777 Jefferson NE, Albuquerque, NM 87109, or to


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