Electrical Conductivity (EC) Explained: A Wildmore Compost Guide

Short answer: Electrical Conductivity (EC) measures how many salts and ions are dissolved in water, soil or compost. For gardeners, EC is a quick snapshot of the nutrient and salt load around roots. It is an important metric for gardeners to be aware of because it affects germination, growth and plant health.

At Wildmore Compost, we have spent almost a decade tweaking our peat free compost blend to ensure that the EC is perfectly balanced for optimum plant growth. That means fewer sudden salt spikes, less seedling stress, healthy roots, and healthier plants. All while protecting peatlands!

This easy guide explains EC in plain language and gives practical steps you can use today: what EC measures, how to test it, what numbers to aim for, and quick fixes when things go wrong.

EC in plain English

What EC actually measures: how well a liquid conducts electricity. That’s determined by dissolved salts and ions (nutrients, hardness minerals, soluble compost salts).
Why gardeners care: too many salts can burn roots and inhibit water uptake; too few salts usually means low nutrient availability. EC helps you balance feeding so plants thrive.
Common units: microsiemens per centimetre (µS/cm) and millisiemens per centimetre (mS/cm). 1 mS/cm = 1000 µS/cm. Most hand meters show one or the other.

Typical EC ranges (quick guide)

Seedlings & cuttings: ~200–800 µS/cm (low is safer).
Most vegetables & mature ornamentals: ~800–2000 µS/cm.
Very sensitive plants (some houseplants): aim lower in the seedling range.

These are general windows. Different species and life stages have different tolerances. When in doubt, start low and feed up slowly.

What changes EC in your garden

Water quality: tap water and hard water raise EC; rainwater is usually lower.
Fertilisers: any soluble feed raises EC. Excessive feeding leads to salt build‑up.
Compost & potting mixes: fresh or immature compost often has higher soluble salts; well‑cured compost is steadier.
Soil texture and moisture: clay holds more ions than sand; wetter samples can show different readings, so test consistently.

EC and soil: what to look for

EC gives a quick picture of salt and nutrient levels near roots. High EC → possible salt stress; low EC → likely low available nutrients.
Tip: test soils near field capacity (moist but not flooded) for consistent results.
Clay soils tend to read higher EC than sandy ones. Organic matter buffers and smooths spikes.

EC and compost: why maturity matters

Fresh/immature compost: often higher in soluble salts. This can stress seeds and young roots.
Mature, well‑cured compost: lower and more stable EC, releasing nutrients gradually.
Wildmore Compost’s peat‑free mix is designed to give a gentle, predictable nutrient release so seedlings and container plants aren’t shocked by sudden spikes.

How to measure EC (simple, reliable methods)

Tools: handheld EC meter (with temperature compensation) or a soil probe for direct readings.

Soil extract (lab‑style) - simple home method:

Mix a measured sample of soil with deionised or distilled water. Common ratios: 1:2 (one part soil : two parts water) or 1:5 for a weaker extract. Use the same ratio every time.
Stir, let solids settle for a few minutes, then measure the clear liquid with your meter.
Note the temperature and meter units (µS/cm or mS/cm).

Potting mix / compost (1:5 extract):

Weigh 50 g compost, add 250 ml deionised water (1:5), shake well for a few minutes.
Let settle, then test the clear extract. Test both fresh and cured samples if possible.

Direct probe (for trays & pots):

Bring the potting mix to field capacity (moist but drained). Insert a soil probe and take several readings across the container for an average.

Interpreting readings & how to adjust EC

If EC is too low:

Plants may show pale leaves and weak growth.
Raise EC gradually with a balanced, low‑salt fertiliser or a gentle liquid feed. Controlled‑release fertilisers are a good option for steady increases.

If EC is too high:

Symptoms: leaf‑edge burn, wilting, slow roots.
Fixes: flush pots thoroughly with clean water, repot into a lower‑salt mix, or dilute strong compost with grit, loam or a low EC blend such as Wildmore Compost. Reduce feeding frequency.

Always make changes slowly - Rapid swings in EC can stress plants more than a steady, slightly off reading.

Practical Wildmore Compost recipes and rules of thumb

Seed trays: use a light seed compost blend to keep EC low for germination. Seeds are packed with their own nutrients, so they need less than mature plants.
Container plants: Generally, container plants enjoy all purpose compost. If the plant is younger, a lower EC compost will suit them better. Wildmore Compost’s all purpose peat free compost is perfect for container plants.
Garden beds: work Wildmore Compost into the top 10–15 cm to increase organic matter without creating a local salt spike.
Watering: use rainwater when you can. If using tap water, occasional deep watering (leaching) helps avoid salt build‑up.

Quick test schedule & record keeping

Test: when potting up, before planting out, mid‑season, and after heavy feeding.
Keep a short log: date, mix, EC, temperature, and any plant symptoms. Small records save a lot of guesswork later.

Troubleshooting (fast fixes)

Salt burn (brown edges, root dieback): flush pot, remove top 2–4 cm of compost, repot if needed.
Poor germination: use a lighter seed mix or dilute compost; test extract and aim for the seedling EC range (200–800 µS/cm).
Stunted growth: test EC; if high, flush and repot; if low, start a gentle feed.

Final notes

EC is a simple, powerful tool: it helps you match feeding to plant needs, avoid stress, and get predictable results. Aim for plant‑appropriate ranges, test new mixes, and adjust slowly.

If you’re using Wildmore Compost: our peat‑free blend is designed to minimise sudden salt spikes and give gentle, reliable nutrient release. Want help with a specific mix or a test result? Contact us! We’re a family‑run team and more than happy to advise.