"What EC should I run for lettuce?" is a question with a two-line answer, which is exactly why it leads people wrong so often. The number in a chart is the EC of the solution you feed a healthy plant in mid-phase with the root zone at a normal temperature. Change the phase, warm the solution, or switch source water, and the same number produces a different plant. What follows collects the target values scattered across this site's crop articles and crop pages, together with the rules that stop a chart from doing harm.
Quick glossary: EC - electrical conductivity of the solution, a measure of total ion concentration; expressed in mS/cm, it reports osmotic pressure rather than how much fertilizer is in the water. pH - the acidity scale from 0 to 14; the hydroponic working range is 5.5-6.5, and it governs the chemical form each element takes and whether the root can absorb it. Drain EC - conductivity of the solution leaving the substrate; the gap between feed and drain shows what the plant took and what is accumulating.
Three Rules Without Which the Chart Does Harm
The number is the feed, not what surrounds the root. The plant lives in whatever solution forms inside the substrate after water and elements have been taken up. Drain EC is what tracks it. The working sign of balance: drain stays 0.3-0.5 mS/cm above feed and does not climb week over week. If drain creeps up, the feed is too strong for these conditions whatever the chart says.
Subtract source water EC first. Recipes are calculated for empty water. Water at EC 0.5 brought up to EC 2.0 delivers 1.5 mS/cm of nutrition and 0.5 mS/cm of ballast from calcium, magnesium and bicarbonates. The same "EC 2.0" on RO water delivers the full 2.0 mS/cm. That is a third of the dose.
Phase matters more than crop name. EC 2.5 is normal for a fruiting tomato and osmotic stress for a tomato seedling in its second week. That is why phase, rather than crop, defines the rows below.
Target EC and pH: Hydroponic Crops
Target EC and pH for hydroponic crops depend on species and growth stage: EC rises from 0.8-1.2 mS/cm for seedlings up to 2.5-3.5 for fruiting tomato and cucumber, while pH stays in the 5.5-6.5 range for most crops.
| Crop and phase | EC, mS/cm | pH | What sets the number |
|---|---|---|---|
| Seedlings and young plants | 0.8-1.2 | 5.5-6.5 | weak root, sensitive to osmotic load |
| Microgreens | 0.8-1.2 | 5.5-6.5 | fed mostly from seed reserves |
| Leafy lettuce and greens | 1.2-2.0 | 5.8-6.2 | narrow pH optimum, tipburn when it drifts |
| Basil and herbs | 1.4-2.2 | 5.8-6.5 | 2.0-2.5 raises essential oil content, above 3.0 burns leaf margins |
| Strawberry, establishment | 0.8-1.2 | 5.8-6.2 | root system not yet developed |
| Strawberry, vegetative | 1.2-1.8 | 5.8-6.2 | calcium and potassium are critical |
| Strawberry, fruiting | 1.8-2.5 | 5.8-6.2 | potassium up, nitrogen down |
| Tomato and cucumber, vegetative | 2.0-2.5 | 5.5-6.5 | active mass growth under full light |
| Tomato and cucumber, fruiting | 2.5-3.5 | 5.5-6.5 | high potassium demand, heavy water uptake |
The upper end of each range works with good light, a cool solution and a healthy root. In heat, under weak light, or when you suspect a root problem, take the lower end: a plant in those conditions draws less water, and the concentration around the root rises on its own.
Target EC and pH: Microgreens by Group
Microgreens feed mostly on what is stored in the seed, so feeding affects the outcome less than water and substrate do. The table gives the most common range found on this site's crop pages rather than the extremes: extremes are pulled by single crops and make the spread look wider than it is.
| Group | Crops on the site | pH | EC, mS/cm | Examples |
|---|---|---|---|---|
| Brassicas | 20 | 6.0-7.0 | 1.0-2.0 | radish, broccoli, kohlrabi, arugula, mustard |
| Herbs | 19 | 6.0-7.0 | 1.0-1.8 | basil, cilantro, dill, parsley, mint |
| Salad crops | 11 | 6.0-7.0 | 0.8-1.5 | lettuce, spinach, amaranth, chard, beet |
| Legumes | 9 | 6.0-7.0 | 0.8-1.5 | pea, mung bean, lentil, alfalfa, chickpea |
| Cereals | 6 | 6.0-7.5 | 0.8-1.5 | wheat, barley, oat, buckwheat, corn |
| Oilseeds | 5 | 6.0-7.0 | 1.0-1.5 | sunflower, flax, chia, milk thistle, caraway |
The upper pH bound here sits higher than in recirculating hydroponics, and that is deliberate. The cycle is short, the substrate is inert, and a micronutrient deficiency has no time to appear in eight days. The same pH 7.0 held on lettuce in NFT for three weeks produces chlorosis in the young leaves.
Why the Chart Gives a Range Rather Than One Number
Root zone temperature. A warmer solution means more active root respiration and faster water uptake. Concentration around the root climbs faster than the meter in the reservoir shows.
Substrate. Coco and rockwool behave differently with identical solution: coco has cation exchange capacity, holds part of the ions and releases them later. One recipe at EC 2.5 delivers different real nutrition on different substrates.
Light. Under weak light the plant grows slowly and takes up fewer elements while transpiring almost as much water. Salts accumulate at a formally correct EC.
The range is deliberate. Inside it you find your own number using drain EC.
Three Mistakes That Cost the Most
Raising EC in response to a symptom. Pale leaves and slow growth read as underfeeding, and the hand reaches for more fertilizer. The cause is usually something else: antagonism from skewed ratios, micronutrients locked out by pH, or osmotic stress that is already present. Raising EC makes all three worse. Measure pH and drain EC first, then act.
Holding pH to a single digit. Element availability across 5.5-6.5 changes gradually rather than in steps, and constant correction with acid adds nitrogen or phosphorus to the solution. A slow drift inside the range is harmless; a daily splash of acid quietly rewrites the recipe.
Taking a chart number meant for different water. A recipe from a forum was built for specific water, a specific substrate and specific light. On hard water with high alkalinity it delivers excess calcium and antagonism with magnesium. A chart is a starting point, not a destination.
How to Know the Targets Are Set Correctly
Feed EC matches the phase, and drain EC stays 0.3-0.5 mS/cm higher without climbing week over week. pH holds inside 5.5-6.5 without daily correction in large doses. The plant is turgid, leaf margins are intact, young leaves show no chlorosis. When the season or the water batch changed, the values were recalculated rather than carried over from last year.
If you want to go deeper: EC in Hydroponics: What Conductivity Shows and Why It Is Not About Fertilizer and pH in Hydroponics: Working Range and Element Availability explain the mechanics every number in this chart came from.