top of page

soil

Soil is not just something that holds a plant upright. It is the system that controls water, oxygen, and nutrient access. A plant can tolerate imperfect watering or light for a time, but it cannot thrive in soil that consistently restricts oxygen or stays wet too long.

Illustrated sprout growing out of soil

what soil does for plants

Healthy soil must:

  • Hold enough moisture to hydrate roots

  • Contain air pockets so oxygen can reach root tissue

  • Provide physical structure for root growth

  • Act as a reservoir for nutrients

If any of these functions fail, root health declines, and the rest of the plant follows.

oxygen is the hidden requirement

Roots are living tissue. They perform cellular respiration, a process that requires oxygen to convert sugars into usable energy (ATP). Without oxygen, roots cannot function, even if water and nutrients are present.

 

This is why soil structure matters more than soil ingredients.

 

When soil becomes dense, compacted, or saturated:

  • Air spaces collapse

  • Oxygen exchange slows or stops

  • Roots suffocate

  • Rot and pathogen growth increase

Most root problems are oxygen problems, not watering mistakes.

soil structure & particle size

Soil performance depends on the size and diversity of its particles.

  • Large particles (bark, perlite, pumice) create airflow and drainage

  • Small particles (peat, coco coir, compost) retain moisture and nutrients

A healthy mix uses both.

Too many fine particles cause soil to stay wet and compact.

Too many coarse particles cause soil to dry too quickly and lose stability.

 

The usual Miracle Gro potting mix that you will find at big box stores works well for a time, but always starts to compact after a few months, which begins to suffocate roots and kick off root rot. Most houseplants are tropical and benefit from amending indoor plant mixes like Miracle Gro potting mix with something chunky, like orchid bark. Even better, try premixed soils, such as Molly’s Aroid Mix, which is designed specifically for plants that need higher drainage but still need to be moist. For cacti and succulents, be sure to get a soil specifically designed for them, which will have a higher sand content and increase drainage while being conducive for their fragile, thin root systems.

 

Remember, the goal is moisture retention with reliable airflow.

soil, light, and water work together

Soil cannot be chosen in isolation.

  • Higher light increases photosynthesis and water use, so the soil will dry faster

  • Lower light slows water uptake, and the soil will stay wet longer

 

Because of this:

  • A soil mix that works well in bright light may cause rot in low light

  • Plants in low light need airier, faster-drying soil

  • Plants in high light can tolerate slightly more moisture-retentive mixes

Soil should always be matched to light levels and watering habits.

nutrients & fertilization

Nutrients support growth, but they do not replace proper light, watering, or soil structure. Plants can only absorb nutrients when roots are healthy and oxygenated. If soil remains compacted or saturated, fertilizer will not help and may cause further damage.

 

Nutrients are taken up by roots dissolved in water, which means soil structure directly controls how efficiently a plant can feed.

macronutrients (npk)

Most fertilizers are labeled with three numbers representing NPK:

  • Nitrogen (N): supports leafy growth and overall vigor

  • Phosphorus (P): supports root development and energy transfer

  • Potassium (K): supports cellular function, resilience, and overall plant health

These numbers represent the ratio of nutrients, not the strength of the fertilizer. A higher number does not mean “better,” and excess nutrients can burn roots or disrupt uptake.

micronutrients

In addition to NPK, plants require small amounts of micronutrients such as:

  • Iron

  • Magnesium

  • Calcium

  • Manganese

While needed in smaller quantities, these are essential for photosynthesis, enzyme function, and structural stability. Most complete fertilizers already include them.

 

Important Note:

If you have a variegated plant that keeps getting brown spots in the white, variegated sections of the leaves, try giving your plant a silica fertilizer. This is reported to help stop variegated plants from browning in their variegated sections.

when fertilizer helps & when it doesn't

Fertilizer is most effective when:

  • Light levels are sufficient for active growth

  • Soil drains well and contains air pockets

  • Roots are healthy and actively growing
     

Fertilizer is least effective, and most dangerous, when:

  • Plants are in low light

  • Soil stays wet for long periods

  • Roots are stressed or damaged

In these conditions, nutrients accumulate in the soil and can cause root burn.

 

Important Note:

There are many that will disagree with this statement, but we put liquid fertilizer in our water almost every single time we water our plants. The fertilizer you use does not have to be strong, the most important thing is that there’s fertilizer at all. There are people that will also say to not fertilize in the winter, but we do it all year round and it does not seem to have a negative effect. Again, this is probably an example of how plants will adapt to whatever you provide them and will be happy as long as you are consistent. We personally like fertilizers that are fish emulsions. They smell funky, but you just need to mix a small amount into your water each time you water your plants.

feeding philosophy

Most houseplants benefit from light, consistent feeding during active growth rather than heavy or infrequent doses. Underfertilizing is far safer than overfertilizing.

A plant growing slowly due to low light or cool temperatures does not need more nutrients — it needs improved conditions.

long-term perspective

Fertilizer supports growth that the environment already allows. Healthy soil, appropriate light, and proper watering create the foundation that nutrients build upon. When those elements are in balance, feeding becomes simple and predictable.

pot choice matters

Even ideal soil can fail in the wrong container.

  • Pots without drainage trap water and eliminate oxygen exchange. (It is almost NEVER correct to use a pot with no drainage)

  • Oversized pots stay wet too long because roots cannot occupy the soil

  • Material matters:

    • Plastic retains moisture longer

    • Terracotta absorbs moisture and increases drying

A good rule: increase pot size gradually, usually no more than 2 inches wider than the previous container.

when to repot

Repotting should be done for soil health, not just plant size.

 

Repot when:

  • Soil stays wet much longer than it used to

  • Roots are densely circling the pot (rootbound)

  • Water runs straight through or pools on top

  • Growth slows despite proper light and watering

Fresh soil restores structure and oxygen, which often triggers new growth.

signs of healthy vs unhealthy soil

Healthy soil:

  • Drains freely but doesn’t dry instantly

  • Feels light and airy when moist

  • Has visible texture and particle variation

 

Unhealthy soil:

  • Stays wet for extended periods

  • Becomes muddy or compacted

  • Smells sour or stagnant

  • Causes recurring yellowing or root loss

If soil in a bag has become hydrophobic (water does not absorb into it), the soil may be expired and it may not be a good choice to plant anything in it.

final notes

Soil does not need to be complicated, but it must be intentional. Most houseplant failures trace back to soil that stays wet too long for the environment the plant is in.

 

Prioritize airflow, match soil to light, and repot when structure breaks down. If roots can breathe, most plants will forgive the rest.

bottom of page