Growing and Gardening in Silty Soil


dry riverbed

Consider yourself lucky if you’re growing or gardening with silty soil.

Next to loamy soil—the gold standard in soils—silty soil tends to be fertile. The irregular shape and small size of its soil particles allows for good aeration. At the same time, it can hold on to water like clay soil but drains better than sandy soil. It can also store plant nutrients better than clay because of its compactable nature.

Silty soil is often a native to river valleys. If your garden is sitting beside a river or was once a riverbed, chances are you may be working with this soil type.

Silty Soil Amendments

So if silty soil is naturally fertile, why would you need to improve it?

That’s because silty soil’s strength is also its greatest weakness: its compactable quality can cause the soil to become too waterlogged. And we know what happens to soil that retains water to saturation point: air can’t circulate, drowning the roots and preventing them from absorbing much needed nutrients.

The first aid to compacted soil is good soil structure—good aeration, better water drainage, and dynamic soil biology for beneficial microbes like mycorrhizae to thrive.

How do you amend silty soil? Two main ways:

1. Add organic matter.

Yearly, amend silty soil with an inch or so of organic matter like compost, thoroughly decayed sawdust, or wood shavings. Add organic fertilizers when needed and cover the soil with 2-3 inches of mulch. The compost will encourage beneficial soil biology to thrive for healthier, hardier plants; the organic fertilizer will act as plant food; and the mulch will protect the plants from drought, erosion and weeds.

Make sure you turn over several inches of the top layer of the soil every so often to keep the soil crumbly and easily manipulated.

2. Avoid compaction.

Because silt is almost as fine as clay, its soil particles could get densely and tightly packed if mishandled.

Minimize walking on garden beds to prevent compacting the soil. One trick is to use narrow boards as pathways between plots or beds, especially in vegetable gardens, where you can walk or stay on when taking care of your garden.

You can also consider planting on raised beds so you won’t need to step on the soil.

Some gardeners amend silty soil by adding clay or sand but this won’t help much in improving it.

raised beds

Watering Silty Soil

Silty soil has numerous tiny air spaces where water can pool that’s why it’s better at water retention than sandy soil. Because it’s good at holding on to water, silty soil tends to become waterlogged like clay soil. To prevent this, avoid overwatering your beds and plots.

Overwatering clogs air pockets, and the lack of breathing space chokes the roots. Too much water in the soil causes rotting roots, which appear as brown, black, grey, or slimy. And because the roots are damaged, they can’t take in the nutrients needed by the plants to survive. (Besides, working silty soil while it’s too wet can damage it and like clay soil, may take a very long while to rehabilitate.)

Overwatering is usually due to repeated watering but if you’re too wary of drowning your plants, there’s a chance that you might be watering too lightly as well.

When plants don’t get enough water, the roots don’t burrow deep enough so they become prone to drought stress. Shallow plant roots will be competing with weeds for nutrients because the latter also love water that’s near the soil surface.

How do you know when it’s the right time to water? When you pinch the topsoil, it’s dry to the touch. You’re drowning your plants if they have light green leaves that’s an unnatural color to the plant, or the foliage is wilted despite the fact that you’ve been watering regularly.

Lastly, make sure that you give the soil time to dry in between watering sessions. This will allow the roots to dig deeper into the soil, avoiding shallow rooting.

weeping willow

Plants for Silty Soil

Growing and gardening with silty soil is almost always a joy because you can grow a broad array of plants. Here are some plants that love wet feet though:

  • Trees and shrubs: weeping willow, bald cypress, red twig dogwood, river birch, red chokeberry, and American elder.
  • Flowers: yellow iris, Japanese iris, and swamp milkweed.

So there you have it, folks: growing and gardening in silty soil. Next time around, we’ll discuss why healthy roots are important to healthy, successful, profitable, sustainable gardens.

Don’t forget to share your own experiences, tips and advice in gardening and growing with silty soil through the comments section below!

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2 Responses to Growing and Gardening in Silty Soil

  1. Green Mountain Boy says:

    Thanks for the information.
    We received 20 truckloads of silty soil from Sugarbush ski area after Hurricane Iriene. They lost the snow making pond there and they were giving the dredge work away for free.
    We needed it to top layer our septic leach field so now is time to grow some grass and wild flower.
    Please let me know if anyone has anymore good ideas.
    I never knew how fertile silt can be, but you are right. It is like quicksand after a heave rain as we are experiencing right now.
    I was thinking of throwing down rye to go along with the wildflower and sections that I want to mow with contractor seed mix.
    Believe me. I live on the side of a mountain so I don’t need Pebble Beach, but just some green cover.

    • Administrator says:

      You are on the right track. Any of your native grasses and wildflowers would help with green-up, stabilization during wet weather plus erosion control. Stick with native species to reduce fertilizing and weed competition. Let us know how it turns out.