Recommended Nutrient Solution Parameters for Hydroponic Herbs

One of the questions we hear most from new growers: "how strong should my nutrient solution actually be?" Every herb has its own sweet spot, and dialing it in is the difference between leggy, bitter growth and the kind of full, aromatic harvest you're after — whether you're running a hydroponic reservoir or an Aero-Gro aeroponic system.

"Herbs are forgiving of a lot of things, but nutrient strength isn't one of them. Get the EC right and everything else gets easier." — Andrew Woodward

Reading your meter: EC, PPM, and microsiemens

Most nutrient meters read out in one of three units, and it trips up a lot of growers:

• EC (electrical conductivity) — measured in milliSiemens per centimeter (mS/cm), or its cousin µS/cm (microsiemens), which is just EC × 1000. An EC of 1.2 mS/cm is the same thing as 1200 µS/cm.
• PPM (parts per million) — most US meters convert EC to PPM using one of two industry scales, "500" or "700." A reading of 1.2 mS/cm shows up as 600 ppm on a 500-scale meter, or 840 ppm on a 700-scale meter. Same water, two different numbers — so always check which scale your meter uses before you compare it to a chart like this one.

The table below gives you EC in mS/cm and µS/cm, plus both PPM scales, so you can read straight off whatever meter you own.

Nutrient strength by herb

Herb	EC (mS/cm)	EC (µS/cm)	PPM (500 scale)	PPM (700 scale)	pH
Basil	1.0–1.6	1000–1600	500–800	700–1120	5.5–6.5
Mint	2.0–2.4	2000–2400	1000–1200	1400–1680	5.5–6.0
Cilantro	1.2–1.8	1200–1800	600–900	840–1260	5.8–6.4
Parsley	0.8–1.8	800–1800	400–900	560–1260	5.5–6.0
Chives	1.8–2.4	1800–2400	900–1200	1260–1680	6.0–6.5
Oregano	1.8–2.3	1800–2300	900–1150	1260–1610	6.0–7.0
Thyme	0.8–1.6	800–1600	400–800	560–1120	5.5–7.0
Dill	1.0–1.6	1000–1600	500–800	700–1120	5.5–6.4
Sage	1.0–1.6	1000–1600	500–800	700–1120	5.5–6.5
Rosemary	1.0–1.6	1000–1600	500–800	700–1120	5.5–6.0
Watercress	0.4–1.8	400–1800	200–900	280–1260	6.5–6.8
Arugula	0.8–1.2	800–1200	400–600	560–840	6.0–7.5

How to use these numbers

• Start at the low end for seedlings and freshly transplanted cuttings, then work up to the higher end as the plant fills out and its root system matures.
• Mint and chives run stronger than most herbs — they're heavier feeders, and under-feeding them is a common reason growers see thin, pale growth.
• Watercress and arugula run leaner — pushing their EC too high tends to show up as tip burn before it shows up as better growth.
• Check pH after you adjust EC, not before — adding concentrate shifts pH slightly, so dial in strength first, then fine-tune pH into range.
• Numbers drift as your reservoir evaporates and plants selectively pull nutrients and water at different rates, so treat these ranges as a target to check back against every few days, not a set-and-forget number.

The bottom line

Most hydroponic and aeroponic herbs cluster between 0.8 and 2.4 mS/cm and a pH of 5.5–6.5 — get in that neighborhood and you're in good shape. From there, the table above is your fine-tuning guide: dial each herb toward its own number rather than running one blanket strength across a mixed herb garden.

Want to check your numbers with confidence? The Aero-Gro Pro 5-in-1 Water Meter reads EC, pH, TDS, and temperature in one dip, and the pH Recalibration Kit keeps your readings accurate over time. For the full picture on feeding your system right, Plant Nutrition is Module 4 of Aero-Gro Academy.