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This hydroponic container size chart gives the smallest jar, bucket or tote that each of 39 herbs, greens, fruiting crops and tray crops needs, along with the net cup size and how far apart to plant them. It answers the questions people actually type into a search bar: how big a reservoir should be, how much water one plant needs, and how many plants fit in a 5-gallon bucket.
Most container charts online are written for soil, so they answer a different question. A pot of soil holds roots and some water. In hydroponics, however, the container is the plant’s whole water and food supply, and if it is too small the level drops before harvest, the nutrient strength climbs and a sunny afternoon can warm the water past the point roots like. If you are new to growing in water, the complete guide to apartment hydroponics covers the basics first. This page, though, is for the moment you are standing in a store holding a jar and wondering whether it is big enough.
How to Read This Container Size Chart
Every row gives four things. The smallest container is the minimum volume for one plant (or one clump, for chives and onions), and where two figures appear, the first is for a passive Kratky jar and the second for an aerated bucket or tote. Kratky then says whether the crop suits a jar with no pump. The net cup is the basket the plant sits in, and spacing is the gap between plants when several share one container.
Minimums, Not Targets
Treat every figure as a floor, not a target. A bigger container is never a problem for the plant, so err on the large side. It holds a steadier temperature and nutrient strength, so it only costs you shelf space and a little more nutrient at each change.
A few cells, however, say varies. For those crops no published figure exists for a hydroponic container, so the honest advice is to give them an aerated tote and their own space rather than a made-up number.
Key takeaways
- Most herbs and loose-leaf greens need only 1 quart per plant in a Kratky jar, which is one wide-mouth mason jar.
- In an aerated bucket or tote, plan on 1 to 2 gallons per leafy plant.
- Fruiting crops are a different scale: 5 gallons per cherry tomato or dwarf cucumber, and 3 to 5 for a dwarf pepper.
- A Kratky jar has to last the whole crop, so size it for the last week, when the plant drinks most.
- A 5-gallon bucket is usually limited by lid space, not water: one fruiting plant, two mizuna, or about three small herbs.
The Full Hydroponic Container Size Chart
The crops are grouped the way they tend to share a shelf, so similar plants sit together. Tap a crop’s name for its full growing guide where one exists, and see the crop sources page for the research behind each figure. In the table, “gal” means US gallons.
Herbs
Herbs are the reason a quart jar became the standard apartment container, since most of them stay small, sip slowly and live happily in one jar each. The woody perennials are the exception, so watch the bottom of this table.
| Crop | Smallest container | Kratky | Net cup | Spacing |
|---|---|---|---|---|
| Sweet basil | 1 quart, or 1 to 2 gal when aerated | Yes | 2-inch | 6 to 8 in |
| Mint | 1 quart, or 1 to 2 gal when aerated | Yes, though roots fill fast | 2-inch | Own container |
| Chives | 1 quart per clump | Yes | 2-inch | 3 to 4 in |
| Garlic chives | 2 to 3 gal per clump | With caution | 2-inch | 8 to 12 in |
| Green onions | 1 quart per clump | Yes | 2-inch | 2 to 3 in |
| Parsley | 1 quart, or 1 to 2 gal when aerated | Yes | 2-inch | 4 to 6 in |
| Cilantro | 1 quart | Yes | 2-inch | 4 to 6 in |
| Dill | 1 quart, or 1 to 2 gal when aerated | Yes | 2-inch | 4 to 6 in |
| Oregano | 1 quart | Yes | 2-inch | 8 to 12 in |
| Thyme | 1 quart | Yes | 2-inch | 6 in |
| Stevia | 1 to 2 gal | Marginal | 2-inch | 8 to 12 in |
| Shiso (perilla) | 1 gal Kratky, but 2 to 3 aerated | In 1 gallon | 2 to 3-inch | 8 to 10 in |
| Sage | 2 to 3 gal | Marginal | 3-inch | 8 to 12 in |
| Rosemary | 3 gal or more | Marginal at best | 3 to 4-inch | 10 to 12 in |
| Lemongrass | 3 to 5 gal per clump | Not in a quart | 3 to 4-inch | 12 in, young |
| Lemon balm | Varies; own tote | Marginal | Varies | About 12 in |
| French tarragon | Varies | Not known | Varies | About 10 in |
The Herbs That Need More Room
Mint gets its own container for a reason. Its roots fill a quart jar fast and crowd anything sharing the water, so give it a jar or bucket to itself. Lemon balm belongs to the same family and gets the same treatment, since its clumping roots are just as pushy.
Rosemary, sage and lemongrass, however, sit at the other end of the scale. They are long-lived and woody, and a single jar that is filled once can’t carry them for months. So treat them as bucket plants from the start.
Leafy Greens
Loose-leaf greens picked young are as easy as herbs, while full heads and the big leafy crops need much more water, because they keep growing for weeks after the quart-jar crops are done.
| Crop | Smallest container | Kratky | Net cup | Spacing |
|---|---|---|---|---|
| Loose-leaf lettuce | 1 quart, but 1 gal to harvest | Yes | 2-inch | 6 to 8 in |
| Romaine lettuce | Varies; aerated tote | Marginal | 2 to 3-inch | 8 to 10 in |
| Butterhead lettuce | Varies; aerated tote | Marginal | 2 to 3-inch | 6 to 8 in |
| Spinach | 1 quart, or 1 to 2 gal when aerated | Yes, kept cool | 2-inch | 4 to 6 in |
| Arugula | 1 quart, or 1 to 2 gal when aerated | Yes | 2-inch | 4 to 6 in |
| Watercress | 1 to 2 quarts per plant | Yes | 2-inch | 8 in |
| Kale | 1 gal baby, but 2 to 3 full | Baby leaf only | 2 to 3-inch | 8 to 10 in |
| Bok choy | 1 to 2 gal aerated | Baby plants only | 2 to 3-inch | 6 to 8 in |
| Swiss chard | 1 to 2 gal | In 1 gallon | 2 to 3-inch | 6 to 8 in |
| Mizuna | 2.5 gal when mature | Yes | 2-inch | 7 in |
| Mustard greens | Varies | Likely, short crop | 2-inch | About 6 in |
| Celery | 5 gal each | Not suited | 3-inch | 6 to 8 in |
The lettuce row has two numbers for a reason. A quart jar grows a loose-leaf lettuce that you pick young, while a full lettuce left to the end needs about a gallon if you want the jar to last without adding anything. For the step-by-step, see growing Kratky lettuce in a jar.
Fruiting Crops and Edible Flowers
This is where container size stops being a detail. Fruit takes a lot of water, so a plant that has set fruit can drink a small bucket low in a few warm days.
| Crop | Smallest container | Kratky | Net cup | Spacing |
|---|---|---|---|---|
| Cherry tomatoes | 5 gal each | Not for beginners | 3 to 6-inch | 12 to 18 in |
| Dwarf peppers | 3 to 5 gal | Hard | 3-inch or larger | About 12 in |
| Dwarf cucumber | 5 gal each | Not suited | 3 to 4-inch | 12 to 18 in |
| Strawberries | 2 to 3 gal | Hard | 3-inch or larger | 8 to 12 in |
| Pea pods | Large, since vines pass 5 ft | Marginal | Varies | 2 to 3 in on a trellis |
| Nasturtium | 1 to 2 gal | Bush types, 1 gallon | 2 to 3-inch | 8 to 12 in |
| Calendula | 1 to 2 gal | Marginal | 2 to 3-inch | 8 to 12 in |
A dwarf cucumber can manage in 3 gallons with careful attention, but 5 is the size that forgives a missed check. And peas are honest work for a small reward: the one documented indoor trial got 12 pods in 55 days from vines over 5 feet tall.
Microgreens and Tray Crops
Tray crops, though, break the per-plant idea. Hundreds of seedlings share one shallow tray and are cut within a couple of weeks.
| Crop | Container | Kratky | Net cup | Spacing |
|---|---|---|---|---|
| Microgreens | 10 by 20 inch shallow tray | Shallow tray | None | Sown densely |
| Micro herbs | Shallow tray | Tray crop | None | Sown densely |
| Wheatgrass | 10 by 20 inch tray | Tray crop | None | Sown densely |
A microgreen tray holds only about 1 to 1.5 inches of depth, which is plenty for a crop harvested at 7 to 14 days. The radish microgreens guide shows a tray from sowing to cutting.
Where these facts come from
🔗 Where these numbers come from The container, Kratky, net cup and spacing figures here are the ones the crop table on this site uses, and the crop sources section links the research behind each crop. The rule that a Kratky jar should be sized to last the crop, with a gallon carrying a lettuce to harvest, comes from B.A. Kratky’s own papers at the University of Hawaii, who developed the method. Where a cell says “varies”, no hydroponic container figure has been published for that crop, so I give practical advice instead of a number.
🌱 Plan this grow: The free Urban Hydro grow planner checks your container against the crops you pick and turns the rest into a day-by-day care list with a harvest date. It runs in your browser, and an account is optional.
Sizing a Kratky Jar So It Lasts the Crop
A Kratky jar is filled once and then left alone, so there is no pump and, in a single jar, no daily top-up. So the volume you start with is the volume the plant has for its entire life, and that is why the size matters more here than in any other system.
At setup, the bottom of the net cup sits in the solution, so the seedling never starts dry. As the plant drinks, the level falls and an air gap forms on its own, usually 1 to 2 inches once the roots are out of the cup. Those upper roots breathe from that gap, while the lower ones drink. The plan only works if the jar still holds water when the plant is at its biggest and thirstiest, which is the last week before harvest.
Quart, Half Gallon or Gallon?
Here is how the common sizes work out in practice:
- 1 quart (a 32 oz wide-mouth mason jar): enough for one herb, a loose-leaf lettuce picked young, spinach or arugula. It is tight for herbs, so it is the minimum, not the comfortable choice.
- Half a gallon: a little breathing room when you want to keep cutting a herb longer, or for baby kale.
- 1 gallon: carries a full lettuce to harvest with nothing added, and it also suits Swiss chard, shiso and bush nasturtium.
If a long crop runs low late on, add a little nutrient solution, not plain water, and raise the level no more than about an inch. Never refill it to the brim, because that drowns the roots that have been breathing from the gap. The full setup, from lid to first harvest, is in the Kratky jar setup guide.
Gear for a Kratky jar
The quart jar in the chart is the easiest start, and these are the parts that turn it into a Kratky system:
- ComSaf 32 oz wide-mouth mason jars: a quart jar, wide enough for a 2-inch cup
- On top go the Kratky wide-mouth lids (24-pack), black discs that sit under the jar’s band with a hole for a 2-inch net cup, so far less light reaches the water from above. Their stock comes and goes, so if they are sold out, this similar Kratky lid kit is the backup pick
- The lids come without cups, so add AC Infinity 2-inch net cups (50-pack)
- To check the solution, the KETOTEK pH, EC and temperature meter reads all three numbers in one pen
The full comparison of cups and lids is in the mason jar net cup guide.
How Big Should a Hydroponic Reservoir Be?
For an aerated bucket or tote, start by adding up the plants. Take the per-plant figure from the chart, multiply by the number of plants, and that is your floor. Four basil plants at 1 to 2 gallons each want a reservoir of at least 4 gallons, and ideally closer to 8.
Then round up, because volume buys stability. A big reservoir changes temperature slowly, and its nutrient strength also drifts less between checks. A small one swings with every warm afternoon, which matters because warm apartments in summer are the number one cause of root problems in small DWC setups. Deeper, covered containers also stay cooler than shallow open ones.
What Changes With an Active System
Unlike a Kratky jar, an aerated system gets a daily top-off with plain pH-adjusted water and a full change every 2 weeks, so it doesn’t need to hold the whole crop’s water at once. That is why the aerated figures in the chart are per plant rather than per lifetime. Above 72°F, add an air stone if you haven’t already, since warm water holds less oxygen. How often to change hydroponic water has the routine, and keeping a small system cool covers the summer side too.
Tip. Once you know your container’s volume, the free pH and nutrient calculator gives the exact nutrient dose for it, so a 2-gallon tote and a quart jar each get the right amount.
How Many Plants Fit in a 5-Gallon Bucket?
A 5-gallon bucket holds plenty of water for most leafy plants, yet water is rarely the limit. What runs out first is room on the lid, which is only about 12 inches across, and the gap each plant needs between its leaves. So the answer depends far more on the crop’s spacing than on its thirst:
- One plant: a cherry tomato, a dwarf cucumber or celery, which each want about 5 gallons to themselves. A dwarf pepper, rosemary or a lemongrass clump also gets the bucket alone.
- Two plants: mizuna, which is documented at two mature plants per 5-gallon bucket.
- About three: small herbs like basil, parsley or thyme, set in a triangle at their 6 to 8 inch spacing. The water would carry more, but the leaves would crowd and invite mildew.
So for several leafy plants, a wide, shallow tote beats a tall bucket every time. It gives each net cup its spacing and still keeps the water volume you need. The Kratky tote setup shows one, and the one-reservoir salad plan lays out six plants in a single tote. For a single big plant in a bucket, the quiet DWC bucket build covers the pump and lid.
Choosing the Container Itself
Size is only half the choice. Whatever you grow in has to keep light away from the water, because light plus nutrient solution grows algae, and algae steals oxygen from the roots. A clear mason jar works only once it is wrapped in an opaque sleeve right up to the lid; stopping algae in hydroponic jars covers the options. Buckets and totes should likewise be opaque, with a lid that fits.
The opening matters too. A wide-mouth jar takes a standard 2-inch net cup, which is also the cup most herbs and greens in the chart use. The bigger plants want a 3-inch cup or more, which means a bucket or tote lid rather than a jar. If you are still choosing between a jar and an aerated bucket, DWC vs Kratky for apartments lays out the trade-offs.
Signs Your Container Is Too Small
Plants tell you quickly when they have outgrown their water. These are the usual signs, and what each one means:
| What you see | Likely cause | Fix |
|---|---|---|
| A Kratky jar runs almost dry weeks before harvest | The jar is too small for this crop | Add up to an inch of nutrient solution now, then use the next size up |
| Roots pack the whole jar, as mint does | The plant has outgrown passive growing | Move it to its own aerated bucket |
| EC climbs fast between checks | The plants drink water faster than they use food | In an active system, top off daily with plain water |
| Brown, slimy roots in a small bucket | Warm, low-oxygen water, which small volumes reach first | Cool it, aerate, and treat the rot |
The last row is the serious one. A small reservoir warms quickly, and since warm water holds less oxygen, root rot follows. Preventing root rot in small systems explains how to stop it before it starts. And once your containers are sized, the hydroponic pH and EC chart gives the strength to fill them with. To see when each crop will be ready, the seed-to-harvest calculator works it out from your sowing date.
One Last Tip
Size for the last week, not the first. A seedling in a quart jar looks lost in all that water, so it is tempting to pick something smaller and tidier. But a plant drinks very little at the start and the most right before harvest, and that is exactly when a small jar runs out. If you are torn between two sizes, take the bigger one. You will never be sorry the water lasted.
Frequently Asked Questions
What size container do I need for Kratky lettuce?
A 1-quart wide-mouth mason jar grows one loose-leaf lettuce that you pick young. To grow a full lettuce to harvest with nothing added along the way, use about a 1-gallon container. Either way, keep it opaque and start with the bottom of the net cup sitting in the solution.
How big should a hydroponic reservoir be?
Add up the plants. Most leafy herbs and greens need 1 to 2 gallons each in an aerated system, so four plants want at least 4 gallons. Then round up, because a bigger reservoir holds a steadier temperature and nutrient strength between checks.
How many plants can I put in a 5-gallon bucket?
It depends on the crop’s spacing more than its water. Put one cherry tomato, dwarf cucumber or celery in a 5-gallon bucket, or two mizuna. Small herbs fit about three to a lid at 6 to 8 inch spacing. For more leafy plants, a wide tote works better than a tall bucket.
Can I grow herbs in a quart mason jar?
Yes. Basil, mint, chives, parsley, cilantro, dill, oregano and thyme all grow in a 1-quart wide-mouth jar with a 2-inch net cup. Wrap the jar in an opaque sleeve to keep out light. Mint fills a jar with roots quickly, so give it a bucket once it outgrows one.
What size container does a hydroponic tomato need?
Give each cherry tomato about 5 gallons in an aerated bucket, with a 3 to 6 inch net cup and 12 to 18 inches between plants. Fruiting plants drink a lot once they set fruit, so a smaller container runs low and warms up quickly in a sunny room.
What size net cup should I use?
A 2-inch net cup suits most herbs and leafy greens and fits a standard wide-mouth mason jar lid. Larger plants such as sage, rosemary, strawberries, peppers and cucumbers need a 3-inch cup or bigger, which means a bucket or tote lid instead of a jar.
Is a bigger hydroponic container always better?
For the plant, yes. More water means steadier temperature and nutrient strength and less risk of running dry. The only costs are shelf space and a little more nutrient at each change. The real mistake is going too small, not too big.
Can several plants share one container?
Yes, as long as each gets its spacing and the crops want similar water. Lettuce, arugula, basil and parsley share a tote well. Keep mint and lemon balm in their own containers, since their roots crowd out neighbors, and give fruiting crops their own buckets.
Does a hydroponic container need to be opaque?
Yes. Light reaching nutrient solution grows algae, which competes with the roots for oxygen. Use an opaque bucket or tote with a fitted lid, or wrap a clear mason jar in an opaque sleeve right up to the lid band.
What if my Kratky jar runs low before harvest?
Add a little nutrient solution, not plain water, and raise the level no more than about an inch. Never refill to the brim, because that drowns the upper roots that breathe from the air gap. Next time, choose a bigger container for that crop.
