Potting Soil Shrinkage

Soil Ingredients

• Potting soil compacts over time, causing it to shrink it the pot. Denser soils compact more quickly, so regular garden soil is rarely used. Using a soil that contains peat, shredded bark or perlite slows compaction and shrinkage. These materials don't break down easily so they maintain aeration in the soil without compacting and shrinkage. Mixtures containing compost quickly shrink as the materials continue to break down in the pot. Choose a potting soil containing both organic and inorganic ingredients to minimize shrinkage.

Under Watering

• Dry soil pulls away from the edges of the pot, giving the impression of shrinkage. The soil has become too dry and has a negative impact on the plant's health once it begins shrinking from the pot sides. Standard watering by pouring water onto the soil won't rehydrate the soil well, since the soil has shrunk to the point where it can readily absorb moisture. Set the pot in a sink of water until the surface of the soil becomes moist. The soil absorbs water slowly through the holes in the bottom of the pot until it's fully rehydrated.

Aging and Decomposition

• Soil breaks down and decomposes, or composts, as it ages. The plant roots also absorb elements and nutrients from the soil, further causing it to shrink. Repotting into fresh soil replenishes the soil that's lost from aging. Lift the entire plant out of the pot and brush as much of the old soil as possible from the plant roots. Replant into fresh potting soil in a pot one size larger than the previous one. Use a pot containing inorganic material or slow to compost materials like shredded bark to slow down the aging process of the soil.

Drainage Concerns

• Excessive drainage causes soil to wash out of the pot, causing soil loss and shrinkage. Pots need some drainage otherwise the soil becomes waterlogged after irrigation, but if the drainage holes are too large the soil washes out with the excess water. Cover the drainage holes in the bottom of the pot with mesh screening before you plant so water can drain, but the soil stays in place. Bottom watering, by setting the pot in a sink of water, also minimizes soil loss through the drainage holes.