Improve Your Soil

Most garden problems start below ground: University of Kentucky specialists trace 80 to 90% of landscape plants’ disease and insect problems to poorly drained soil^[1]. These guides fix soil in order, drainage first and then organic matter, each built on extension guidance and checked against USDA’s soil maps.

Work in order: five steps

The plan, from extension guidance^[3][1][2]:

1. Test the soil. A soil test decides whether pH needs adjusting^[3], and an annual test is Colorado State’s best measure of whether you need compost^[2].
2. Fix drainage first. A perk test of about 2 inches an hour is good, 1 to 3 is acceptable and under 1 is poor; redirect water from uphill and from downspouts, or build raised beds or berms on wet sites^[1].
3. Add organic matter, mixed thoroughly into new beds^[4]: 3 to 4 inches of compost worked into the top 8 to 12 inches of a new garden^[2].
4. Protect it. Mulch the surface and keep traffic off the beds so the soil doesn’t compact^[2].
5. Top it up: about a quarter inch of compost a year in beds you dig^[2], or up to an inch a year left on top of beds you don’t dig and lawns^[5][6].

Guides

• Improve garden soilA five-step plan: test, fix drainage, add organic matter, protect it and top it up.
• Improve soil drainageTest drainage with a perk test, then fix it: raised beds, redirected water, rain gardens.
• Fix compacted soilSpot compaction, find the cause, and loosen it with aeration and organic matter.
• Improve sandy soilWhat to add to hold water and nutrients, how much, and how to start a lawn on sand.
• Best grass for sandy soilDrought-tolerant lawn grasses by climate, with extension ratings and care tips for sand.
• Amend clay soilWhat works on clay, and the sand-in-clay mistake to avoid.
• Compost for clay soilWhich compost opens clay, and how deep to work it in.
• Raise or lower soil pHLime raises pH, sulfur lowers it. Extension rates by texture and a calculator for your area.
• Soil amendmentsWhat each amendment does, how much to add, and which ones to skip.

Sand and clay need different fixes

In clay, don’t add sand to poorly drained ground^[1], and skip gravel, which makes drainage worse^[4]; fibrous compost such as composted wood chips or straw opens clay up. Sandy soil does better with well-decomposed material, finished compost or aged manure, to hold water and nutrients^[2]. The clay guide and the sandy soil guide go through both in detail.

If drainage can’t be fixed

Some sites stay wet whatever you do. University of Kentucky specialists suggest raised beds or berms there, and warn against piling large amounts of organic matter onto poorly drained soil. They also list trees and shrubs that tolerate wet ground: red maple, swamp white oak, blackgum, bald cypress, buttonbush, summersweet and winterberry holly^[1]. The drainage guide covers the perk test and the fixes in detail.

Amendments to skip

Some fixes make things worse. Colorado State lists gravel, which makes drainage worse; raw wood, which ties up nitrogen until it is composted; fresh manure, which should never go on as an amendment or mulch because of E. coli; and manure composts, which are often salty^[4]. The amendments guide goes through what each one does.

When the problem is compaction

Compacted soil is too dense for roots. NRCS gives a bulk density at which roots are restricted for each texture, from 1.47 g/cm³ in clay to 1.8 g/cm³ in sand and loam^[7]. Measure yours with the bulk density calculator, and see the compaction guide for how to loosen it.

Getting the pH right

Most vegetables do best between pH 6 and 7, blueberries, azaleas and rhododendrons between 4.5 and 5.5, and lawns between 5.5 and 6^[3]. Lime raises pH and sulfur lowers it; sulfur reacts slowly, so work it into the soil^[8]. The pH guide has rates by texture and a calculator for your area.

Plants for your soil

Rather than change the soil, pick plants that already tolerate it.

• Plants for clay soilPerennials, shrubs and trees that tolerate clay, with picks for wet clay, from extension lists.
• Plants for sandy soilTrees, perennials and grasses for dry, sandy ground, from extension lists for tough sites.

Want the background first? See learn about soil.