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Sand, Silt, and Clay - Oh My!

Sand, Silt, and Clay - Oh My!

By Miranda Niemiec for Proven Winners® ColorChoice®
Photographs courtesy of Proven Winners® ColorChoice®

When we think about gardens, we usually envision the leaves, stems, and flowers of plants, but what about growth below ground? The roots are considered to be the “hidden half” of the plant. They’re essential to the plant’s success, providing anchorage and absorbing water and nutrients from the soil. The type of soil heavily influences plant growth, which is why it’s important to know what’s happening below ground in your garden!

In this article, we will walk you through the three main soil categories (clay, silt, and sand) and give insight into what that means for your plants. Not sure what kind of soil you have? Don’t worry; we’ll teach you how to identify it.

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Kodiak Orange Diervilla

Digging Deeper: Clay Soil

Clay particles are small and flat, packing tightly together. However, its small size means it has a larger specific surface area (surface area for a given mass). There are a few reasons why this is important:

The greater the surface area, the greater capacity it has to hold onto nutrients.

Small soil particles are more likely to stick together in masses. It feels thick and sticky when wet, then dries into hard clods.

Small particles have less pore space, which means water has less room to percolate through the soil.

What does this mean for your garden? First of all, it’s easier to overwater plants in clay soils. Since the water doesn’t drain quickly, the soil is prone to waterlogging, which can be fatal. Limiting the air in the soil literally drowns the roots! Another issue clay can cause in your garden is compaction. The small, flat soil particles easily push together, reducing pore space even further. This can lead to reduced aeration, an inability to cycle nutrients, and poor root penetration. However, clay soils aren’t all bad. They tend to be nutrient-rich, as the negatively charged particle surfaces hold onto positively charged particles of essential micronutrients.

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Paraplu Pink Ink hibiscus

Watering is the biggest challenge gardeners face with heavy clay soils. The best approach is to water less frequently with more water to prevent waterlogging and encourage deep root growth. Plus, it’s way easier to recover from under watering than overwatering. It’s beneficial to plant slightly above the soil line in poor-draining soil to improve aeration at the crown. Raising the plant just a little bit should do the trick.

Avoid further compaction by not over-tilling, walking on garden beds, or using heavy machinery when planting. Also, avoid working with the soil when it is wet. Is the clay sticking to your shovel? If so, take a break and let the soil dry out. Overworking wet clay soil will ruin the structure and lead to further compaction.

Since clay already holds onto nutrients well, you can use a light hand when fertilizing. Keep in mind that holding onto minerals may not always be helpful since it can hold onto bad minerals (like salt) as well. 
 
Clay soils may not be ideal, but some shrubs will grow well in it, like Aronia (chokeberry), Diervilla, and Hibiscus syriacus (rose of Sharon). For a low groundcover plant, try Ground Hug® (8-14”, USDA Plant Hardiness Zones 3-9) or Low Scape Mound® Aronia (1-2’, zones 3-9). For a shade-tolerant foundation plant, Try Kodiak® Orange Diervilla (3-4’, zones 4-7), and for a splashy specimen, add Paraplu Pink Ink® Hibiscus to your landscape plan (5-8’, zones 5-9).

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Incrediball native smooth hydrangea

Digging Deeper: Silt Soil

Silt shares similar properties as clay – smaller particle size, small pore spaces, and larger specific surface area. However, the silt particles are slightly larger and irregular in shape, which solves a lot of the problems we see in clay. Here are some notable properties of silt:

Small particles with a large surface area hold onto nutrients well. The size leads to rapid weathering, which releases a significant amount of plant nutrients.

Particles are irregularly shaped and aren’t as likely to stick together.

There is less pore space, which means there is high water retention.

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Limelight Prime panicle hydrangea

Silt soil is great in your garden because it is generally very fertile. The particle surface holds onto an abundance of nutrients, plus it releases even more nutrients as it quickly weathers. Moisture-loving plants tend to love growing in silt soils. While it has high water retention with small pore spaces, it does have better drainage than clay. This is thanks to the irregular particle shapes, which won’t stick together. Because they don’t stick together, there is less compaction, more pores, and better aeration for roots. However, this does lead to one major problem. Silt is highly susceptible to water erosion, as particles that don’t stick together are easily washed away.

If silt soils become compacted, they take on many of the problems we see in clay soils. Be careful when walking on garden beds, using any machinery, and over-tilling when planting to avoid this. To prevent water from pooling on the surface of the ground or washing away, give the soil time to dry between waterings. If you’re careful with your silt soils, your plants will be thankful!

Hydrangeas will grow just fine in silt soil. Try a native smooth hydrangea, like Incrediball® H. arborescens (4-5’, zones 3-8), or an easy to grow panicle hydrangea like Limelight Prime® H. paniculata (4-6’, zones 3-8).

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Lo & Behold ‘Pink Micro Chip’ butterfly bush

Digging Deeper: Sandy Soil

Sand particles (or grains) are likely the most familiar, mainly because they are visible to the naked eye and have a coarse texture. They are primarily composed of quartz or other silicates. These particles are the largest of the three, which makes a big difference in your soil for a few reasons:

Large particle size means a smaller specific surface area, so they have little capacity to hold onto water and nutrients.

There are larger pore spaces, which means water drains quickly through the soil.

The sand particles are resilient to compaction.

Let’s start with what we love about having sandy soil in the garden. One of the first things you’ll notice is that sand particles won’t stick together, making it easy to dig. It also makes them resilient to compaction. This is great news for roots because non-compacted soils are well aerated and easier to grow through. Plants that prefer dry soils grow well in sand. There is great drainage in sandy soils, so you won’t need to worry about overwatering. The large pore spaces allow water to move through the soil profile quickly. While this solves the problem of waterlogging, it causes new problems. Sharp drainage means the soil is prone to drought and is infertile.

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Miss Molly’ butterfly bush

Water that moves quickly through the soil also carries away essential water-soluble nutrients, like nitrogen. This is a problem considering sandy soils aren’t known to be very fertile in the first place. Sand particles weather slowly and don’t release many nutrients for plants in the process. Plus, the small specific surface area means it can’t hold onto many nutrient ions.

There are a few strategies to remember while gardening in sandy soils. Encourage deep root growth by watering deeply with less frequency. Roots will “chase” the water and penetrate deeper into the soil profile, helping the plant access deep water and nutrient reserves. Choose slow-release fertilizers over liquid fertilizers to lower the risk of nutrient leaching.

Sandy soils may have some weaknesses, but they’ll still support a wonderful garden. For instance, butterfly bushes require very well-drained soil and will thrive in sandy sites. The ‘Miss’ and Lo & Behold® series of Buddleia are non-invasive too, making it truly worry-free. For a large, showy bush, try the deep red-pink blooms of ‘Miss Molly’ Buddleia. It will grow to 4-5’ tall and wide and is hardy in zones 5-9. For something smaller, Lo & Behold® ‘Pink Micro Chip’ will mature to just 1.5-2’ tall and wide with the same hardiness. Both will bring pollinators to your garden in droves.

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Low Scape Mound Aronia 

Not Sure What Type Of Soil You Have?

The quick and dirty way of finding out is by using your hands. Make a little hole in your garden, approximately six inches deep, and grab a chunk of soil. Mix it with a small amount of water in your hand and try to form a ball, then add more water and rub it tight between your fingers.

  • If you can form a ball easily, it’s likely clayey soil. It will feel sticky when wet, especially when you rub it between your fingers.

  • If you can almost form a ball, but not quite, it’s likely silty soil. When wet, it will feel silky and smooth between your fingers.

  • If there is no hope of forming a ball, it’s likely sandy soil. When you rub it between your fingers, it feels coarse and grainy.

If you want to know which Proven Winners® ColorChoice® shrubs will thrive in your soil, check out the detailed search page of MyPWColorChoices.com. You can sort by uses, features, bloom time, and more, making it easy to choose shrubs that will perform best in your garden conditions.


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