Start with light, substrate, and CO2 to build the foundation
A planted aquarium grows plants underwater by giving them three things: light strong enough to reach the bottom, a substrate (soil or gravel) that holds nutrients, and carbon dioxide. Most beginners skip one of these and watch their plants yellow and die. You do not need all three at maximum strength — a low-tech setup with basic lighting and no added CO2 works fine for hardy plants like Java fern and Anubias — but you need all three present.
Light is the first place most people go wrong. Standard aquarium hoods with incandescent bulbs do not produce enough light for plants to photosynthesize at the speed they need. You need LED lights rated for planted tanks, positioned 8 to 12 inches above the water surface, running 8 to 10 hours per day. Lights that cost $40 to $80 and sit on top of the tank work. Lights built into the hood often do not. If your plants are pale or growing sideways toward the glass, light is the culprit.
Substrate matters because plant roots absorb nutrients from it. Sand, aquarium soil, or gravel all work, but aquarium soil (brands like Flourite or ADA Aquasoil) holds nutrients longer and does not need replacement as often. Gravel alone will starve plants over time unless you add fertilizer pellets under it. Depth should be 2 to 3 inches — enough for roots to anchor and absorb, not so deep that it traps gas pockets that rot the roots.
Carbon dioxide (CO2) is optional for slow-growing plants but necessary if you want fast growth or plants with fine, delicate leaves. A pressurized CO2 system with a regulator and diffuser costs $150 to $300 to set up. Liquid carbon supplements (like Flourish Excel) are cheaper and work for low-tech tanks, though they are not true CO2. If you are starting out, skip CO2 and pick plants that grow without it — you can add it later.
Key Takeaways
- LED lights rated for planted tanks, positioned 8 to 12 inches above water and run 8 to 10 hours daily, are the single most common missing piece in failing planted tanks.
- Aquarium soil holds nutrients longer than gravel alone and should be 2 to 3 inches deep to support root growth.
- CO2 is optional for hardy, slow-growing plants but required if you want fast growth or delicate-leaved species.
- Fertilizers replace nutrients that plants consume; all-in-one liquid fertilizers work for beginners and cost $10 to $20 per bottle.
- Plant stems and roots need 4 to 8 weeks to establish before you expect visible growth above the substrate.
Choose plants matched to your light level and tank size
The plants you pick determine whether your tank thrives or becomes a graveyard. Beginners often buy the most beautiful plant in the store without checking whether it will survive their setup. A plant that needs high light will melt and disappear in a low-light tank within weeks, no matter what else you do right.
Low-light plants (need 1 to 2 watts per gallon or less) include Java fern, Anubias, Cryptocoryne, and Bucephalandra. These are nearly impossible to kill and grow slowly enough that you will not need to trim them constantly. Tie them to rocks or driftwood with fishing line — do not bury the rhizome (the thick horizontal stem at the base) or it will rot. These plants do not need fertilizer if you do water changes weekly.
Medium-light plants (2 to 3 watts per gallon) include Ludwigia, Rotala, and stem plants like Bacopa. These grow faster, need trimming every two weeks, and benefit from liquid fertilizer added twice weekly. They are forgiving enough for a second tank but will not thrive under low light.
High-light plants (3+ watts per gallon) include Glossostigma, Hemianthus callitrichoides, and most red-leaved plants. These demand strong light, CO2, and fertilizer. Start with them only if you have already kept medium-light plants successfully.
Tank size matters too. A 10-gallon tank is small enough that one large plant (like a sword plant) will shade everything else. A 20-gallon long tank gives you room to arrange plants by height — tall plants in back, short plants in front — so light reaches all of them. If you have a small tank, stick to plants that stay under 6 inches tall.
Plant stems and roots correctly to prevent melt and rot
How you plant matters as much as what you plant. Stem plants (Ludwigia, Rotala, Bacopa) are planted by burying the bottom 1 to 2 inches of the stem in substrate. Remove the lower leaves first so they do not rot underwater. Space them 1 to 2 inches apart so light reaches all sides. If you crowd them, the inner leaves will yellow and drop.
Rooted plants (swords, Cryptocoryne, Echinodorus) are planted deeper — bury the roots and the base of the plant, but leave the crown (where the leaves meet the roots) at or just above the substrate surface. If you bury the crown, it will rot. If you plant too shallow, the roots will not anchor and the plant will float up.
Rhizome plants (Java fern, Anubias, Bucephalandra) should never be buried. Tie them to a rock or piece of driftwood with fishing line or plant weights. Bury the rhizome and it will rot within days. The roots will grow down into the substrate on their own.
New plants often melt — the leaves turn translucent, brown, and fall off. This is normal. The plant is adjusting to underwater life. Do not throw it out. Keep the light on, do water changes, and the plant will usually regrow within 2 to 4 weeks. Stem plants that melt will send up new shoots from the base. Rooted plants will push new leaves from the crown.
Add fertilizer on a schedule that matches your water changes
Plants consume nutrients from the water column and the substrate. In a new tank with fresh substrate, you have enough nutrients for 4 to 8 weeks. After that, plants start to yellow and slow down. Fertilizer replaces what they consume.
All-in-one liquid fertilizers (brands like Thrive, Flourish, or Comprehensive) contain nitrogen, phosphorus, potassium, and trace minerals in one bottle. Dose them twice per week at the rate printed on the bottle — usually 1 to 2 milliliters per 10 gallons. If you do a 50% water change weekly, dose after the water change so you do not dilute the fertilizer when ready.
Watch your plants for signs of deficiency. Nitrogen deficiency shows as pale or yellow older leaves (the plant pulls nitrogen from old growth to feed new growth). Potassium deficiency shows as holes in the leaves. Iron deficiency shows as yellow new growth with green veins. If you see these, increase fertilizer dose by 25% or switch to a fertilizer with higher levels of the missing nutrient.
Overdosing fertilizer does not kill plants — it feeds algae instead. If you see green water or thick algae growth, cut fertilizer in half and do a 50% water change. Algae thrives on excess nutrients and light, so the fix is usually less fertilizer, fewer light hours, or more frequent water changes.
Do water changes weekly to remove waste and replenish minerals
Water changes are not optional in a planted tank. They remove fish waste (which becomes ammonia), replenish minerals that plants consume, and dilute excess fertilizer that feeds algae. A 25% to 50% water change once per week is the standard for planted tanks with fish.
Use a siphon or gravel vacuum to remove water from the bottom of the tank, where waste settles. This also stirs up the substrate and prevents gas pockets from forming. Replace the water with dechlorinated water at the same temperature as the tank — cold water shocks the plants and fish. If your tap water is very hard or very soft, you may need to adjust it, but most tap water works fine for planted tanks.
If you keep the tank for several months without water changes, the substrate becomes compacted and anaerobic (lacking oxygen). Roots rot, plants yellow, and the tank smells like rotten eggs. Weekly water changes prevent this entirely. If it happens, do a 50% water change when ready and loosen the substrate with a stick or your fingers.
Trim and propagate plants to control growth and fill the tank
Fast-growing stem plants like Ludwigia and Rotala will reach the surface and shade everything below them within 4 to 6 weeks. Trim them when they reach the top by cutting the stem 1 to 2 inches below the water surface. The plant will branch and send up two new shoots from the cut point. Remove the top portion and replant it in the substrate — it will root and grow into a new plant.
Trim every two weeks once the plants are established. This keeps them bushy instead of tall and leggy, and it gives you cuttings to replant and fill empty spaces. If you do not trim, the plant will grow straight up, shade the bottom of the tank, and eventually reach the surface and stop growing.
Slow-growing plants like Java fern and Anubias rarely need trimming. Remove only dead or damaged leaves by cutting them at the base with scissors. New leaves will grow from the rhizome to replace them.
Rooted plants like swords will send up runners (horizontal stems) that produce baby plants. Once the baby has 4 to 6 leaves, cut it free from the runner and plant it in the substrate. The original plant will send up more runners, and you can keep propagating indefinitely.
Watch for common problems and fix them early
Algae is the most common problem. Green water, green slime on the glass, or brown algae on the substrate all mean light is too strong, fertilizer is too high, or water changes are too infrequent. The fix is usually one of three things: reduce light to 6 to 8 hours per day, cut fertilizer in half, or do water changes twice per week instead of once. Do not use algae-killing chemicals — they kill plants too.
Yellowing leaves mean either low light, low fertilizer, or old age. If the oldest leaves (at the bottom) are yellow and the new growth is green, the plant is just shedding old leaves — this is normal. If all the leaves are pale yellow, increase light or fertilizer. If the new growth is yellow, the plant is deficient in nitrogen or iron.
Melting leaves on new plants are normal and usually resolve in 2 to 4 weeks. Melting on established plants that were growing fine means the plant is stressed — usually by a sudden change in light, temperature, or water chemistry. Check that the heater is working, the light is still on the right schedule, and you did not skip a water change.
Stunted growth (no visible change in 4 weeks) means light, fertilizer, or CO2 is too low for that plant. Move the plant closer to the light, increase fertilizer dose, or switch to a plant that grows slower. Do not assume the plant is dead — many plants grow so slowly that you will not see change for 8 weeks.
Frequently Asked Questions
Do I need CO2 to grow plants in an aquarium?
No. Hardy, slow-growing plants like Java fern, Anubias, and Cryptocoryne grow without added CO2. Fast-growing stem plants and red-leaved plants benefit from CO2 but will survive without it if you have strong light and fertilizer. CO2 is optional, not required.
How long does it take to see growth in a new planted tank?
Most plants take 4 to 8 weeks to establish roots and show visible new growth. Stem plants may melt for the first 2 weeks, then regrow. Do not assume a plant is dead if nothing happens for a month — many plants grow so slowly that change is invisible week to week.
Can I use regular aquarium gravel instead of aquarium soil?
Yes, but plants will need fertilizer sooner. Aquarium soil holds nutrients for 4 to 8 months. Regular gravel holds them for 2 to 4 months. Both work if you do water changes weekly and add liquid fertilizer twice per week. Aquarium soil just requires less fertilizer overall.
What should I do if my plants are growing toward the light instead of upward?
This means light is too weak or too far away. Move the light closer (8 to 12 inches above the water surface) or replace it with a stronger LED. Weak light is the most common reason planted tanks fail. If the light is already close and strong, the plant may need more light than your setup provides — switch to a slower-growing plant.
How often should I trim my plants?
Fast-growing stem plants need trimming every 2 weeks once they reach the top of the tank. Slow-growing plants like Java fern and Anubias rarely need trimming — remove only dead leaves. Rooted plants like swords need trimming only if they grow too large for the tank.