Starting plants from seeds is an extremely rewarding and budget-friendly way to grow flowers, vegetables, herbs, and more. While the seed itself contains all the nutrients needed for germination, seedlings require additional fertilizer for robust growth once their first true leaves emerge. However, knowing when and how much to feed seedlings can be tricky. Apply too much fertilizer too early, and you risk burning delicate roots. Apply too little, and your seedlings will fail to thrive. This complete guide covers everything you need to know about choosing and using the best plant food for your seedlings.
When to Start Fertilizing Seedlings
Seeds contain a food packet called the endosperm that provides all the nutrients required for germination and early seedling growth This allows seeds to sprout and form their first set of embryonic leaves called cotyledons without any additional fertilizer
Once the first set of true leaves emerges above the cotyledons the seedling exhausts its stored food reserves and requires supplemental nutrition. This is the best time to begin fertilizing with a dilute solution. Most experts recommend waiting until seedlings are at least 2-3 inches tall and have 1-2 sets of true leaves before starting fertilizer applications.
Starting too early with full-strength fertilizer can damage tender roots and leaves. Delaying too long can result in stunted, yellowed growth. Pay close attention and begin feeding at the first sign of true leaves for best results.
How Often Should You Fertilize Seedlings?
When first starting fertilization, begin with a dilute solution once a week. After a couple applications, you can increase frequency to 2-3 times per week if needed.
Here is a typical feeding schedule:
- Weeks 1-2: No fertilizer
- Weeks 3-4: Dilute solution once per week
- Weeks 5-6: Dilute solution 2-3 times per week
Reduce applications if you notice signs of fertilizer burn like browning leaf tips. Increase frequency if seedlings appear pale or stunted. Tailor the schedule based on each plant’s unique needs.
Best Fertilizers for Seedlings
Seedlings need more phosphorus and potassium than nitrogen to develop strong roots and stems. Look for fertilizers with a higher phosphorus and potassium content compared to nitrogen, or choose a balanced formula.
Liquid fertilizers are fast-acting and easy to dilute to the proper concentration for seedlings. They provide immediate nutrient availability.
Granular or powder fertilizers release nutrients more slowly over time. Mix granules into seed starting mix when potting up seedlings for continuous feeding.
Organic fertilizers like compost tea, fish emulsion, kelp, and worm castings supply nutrients without synthetic chemicals. They are gentler on tender seedling roots.
Here are some top-rated fertilizers for seedlings:
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FoxFarm Liquid Plant Food (6-4-4) – Concentrated liquid provides fast nutrient uptake.
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Miracle-Gro Shake ‘N Feed (8-7-6) – Granules feed up to 3 months. Shake over soil.
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Jobe’s Organics Vegetable & Tomato Granular Fertilizer (3-1-2) – Slow-release organic granules.
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Maxicrop Liquid Seaweed (0-0-1) – Concentrated seaweed extract stimulates growth.
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Worm castings – Naturally high in nutrients and beneficial to soil. Mix into seed starting soil.
How to Apply Fertilizer to Seedlings
Follow these tips when feeding your seedlings:
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Always dilute liquid fertilizers to 1/4-1/2 strength to avoid burning roots.
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Water seedlings thoroughly before fertilizing to prevent root damage.
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Apply fertilizer right at the base of the stem to prevent leaf burn. Avoid contact with leaves and stems.
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Pour diluted liquid fertilizer into the drainage holes at the bottom of pots. This is called “bottom feeding” and prevents fertilizer buildup.
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Mix granular fertilizers into potting soil at the time of potting up seedlings according to label rates.
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Use a foliar spray only occasionally. Mist diluted liquid fertilizer directly onto leaves.
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Never apply dry granular fertilizer directly on top of seedling leaves. This causes burning.
Follow fertilizer labels closely and reduce rates if you notice any tip burn or yellowed lower leaves, which are signs of over-fertilization. It’s always better to underfeed seedlings rather than overdo it on fertilizer.
Potting Up Seedlings
When seedlings outgrow their starter cells or trays, it’s time to “pot up” into larger individual containers. This gives their roots more room to expand. Take this opportunity to give seedlings an extra dose of nutrients by amending the potting mix.
Here are some amendments to mix into potting soil when moving seedlings into larger pots:
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Worm castings – Mix 1-2 tablespoons per gallon of soil. Provides many nutrients.
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Compost – Mix 1 part compost into 2 parts potting mix. Boosts nutrient content.
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Granular fertilizer – Mix according to label rates, usually 1-2 tablespoons per gallon of soil.
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Mycorrhizae fungi – Mix in powder to boost root growth.
Feed with liquid fertilizer 1-2 weeks after potting up once roots establish in their new containers.
Troubleshooting Seedling Fertilization Issues
Here are some common seedling fertilization problems and how to solve them:
Yellow, stunted growth: Seedlings need more fertilizer. Increase frequency and concentration of liquid feeds.
Burned leaf tips: You over-fertilized. Flush soil with plain water and resume feeding at a lower concentration.
Leggy, weak stems: Seedlings lack proper light. Move to a sunnier location before resuming fertilizer.
Damping off disease: Over-fertilization can cause fungal issues. Allow soil to dry out before watering and fertilizing again.
White crusty deposits on soil: You over-fertilized, causing salt buildup. Flush soil and resume at lower rates.
Severe leaf burn: Granular fertilizer made direct contact with leaves. Water immediately to wash off.
Adjust your fertilizer regimen based on seedling health and response. Their needs change rapidly as they grow. With the proper feeding schedule, you’ll have stocky, vibrant, healthy transplants ready for the garden!
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Expert tips on when to fertilize seedlings
If you are sowing your plants from seed, then choosing the best soil to start seeds in is key. The best choice is specialist seed compost and this is because, as Ruth Hayes, Gardening Editor for Amateur Gardening, says: ‘There is enough nutrients in seed compost to start seedlings without needing extra fertilizer.’ Seeds do not need the additional nutrients or feed to germinate that other composts, including multipurpose compost and homemade compost, often contain.
Seeds contain all the power they need to germinate and the smallest seedlings can survive merely off the stored food in the seed. The seedling relies on that source until it has its first true leaves and starts the process of photosynthesis. Seedlings do not need any fertilizer during that early stage of their growth and applying feed too early can actively harm them.
The earliest seedlings can be given fertilizer is when they have their first set of true leaves and hit around two inches tall. However, when I was running propagation regimes and growing lots of plants from seed annually, I always added fertilizer when the plants were being pricked out of their seed trays, or potted up into larger modules. They tended to be pricked out when they had at least their second set of true leaves and were large enough to handle. This normally was around three or four weeks after sowing.
Potting on offers a great time to fertilize seedlings ( credit: Getty/Jordan Lye)
Do seeds germinate faster if fertilizer is applied?
No, seeds do not germinate faster with fertilizer than without. The seeds do not actually need fertilizer for the first few weeks of their life. It would be a seed sowing mistake to feed too early as germination can actually be hindered if there is too much fertilizer in the soil. It is always recommended to hold off applying fertilizer until the seedlings have developed their true leaves.
What is the Best Fertilizer for Seedlings?
FAQ
What is the best fertilizer for seedlings?
It is best to opt for a balanced fertilizer or one with a higher ratio of nitrogen and phosphorus. You can use either liquid or granular fertilizers to feed seedlings, but never apply fertilizer at a rate higher than recommended on the container.
Can I use plant food on seedlings?
- When to Start Fertilizing: Wait until your seedlings have developed their first set of true leaves (the leaves that resemble the adult plant’s leaves) before starting to fertilize. The initial leaves that emerge are called cotyledons or seed leaves, and they contain the nutrients needed for early development.
- Type of Fertilizer: Use a water-soluble, all-purpose fertilizer designed for young plants.
- Dilution: Always use a diluted solution of fertilizer, typically around 1/4 to 1/2 the recommended strength for mature plants. Over-fertilizing can damage or kill seedlings.
- Frequency: Fertilize every 7-10 days or as recommended by the fertilizer manufacturer.
- Application: Apply fertilizer to the soil, not directly on the leaves or stems.
- Signs of Over-Fertilization: Watch for signs of fertilizer burn, such as yellowing or browning of leaf tips, or stunted growth.
- Alternatives: Some gardeners prefer to use organic fertilizers like fish emulsion or seaweed extract, which are gentler on seedlings.
Is Miracle-Gro good for seedlings?
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Miracle-Gro Seed Starting Potting Mix:This mix is specifically formulated for starting seeds and plants, and is enriched with plant food to help seedlings get off to a strong start.
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Quick Start Planting and Transplant Starting Solution:This solution is designed to improve root growth and is ideal for all types of plants, including seedlings.
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Seed Starting Plant Food:Miracle-Gro also offers a seed starting plant food specifically designed to nourish seedlings and help them develop strong roots.
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When to use:Use Miracle-Gro products when starting seeds or plants from cuttings, and consider using the Quick Start solution when transplanting seedlings.
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How to use:Follow the instructions on the product packaging for proper application and dilution, especially when using the liquid fertilizer.
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Considerations:While Miracle-Gro can be effective, some gardeners prefer organic alternatives or use Miracle-Gro at a diluted rate for seedlings.
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Alternatives:If you are looking for organic alternatives, you could try compost, composted manure, fish emulsion, or worm castings.
How to boost seedling growth?
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Light:Seedlings need sufficient light, either natural sunlight or grow lights, to photosynthesize and grow properly.
- Natural Light: Place seedlings near a sunny window, or supplement with grow lights if needed.
- Grow Lights: Use grow lights that provide the necessary wavelengths of light for plant growth.
- Natural Light: Place seedlings near a sunny window, or supplement with grow lights if needed.
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Water:Keep the soil consistently moist, but not waterlogged, as both extremes can harm seedlings.
- Watering Technique: Water thoroughly when the top inch of soil feels dry, and ensure the pots have drainage holes.
- Watering Technique: Water thoroughly when the top inch of soil feels dry, and ensure the pots have drainage holes.
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Temperature:Maintain a warm temperature, ideally between 65-75°F (18-24°C), especially during the early stages of growth.
- Temperature Fluctuations: Avoid extreme temperature fluctuations, as these can stress seedlings.
- Temperature Fluctuations: Avoid extreme temperature fluctuations, as these can stress seedlings.
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Fertilization:Once seedlings have a few sets of true leaves, start fertilizing with a weak solution of balanced fertilizer.
- Fertilizer Type: Use a water-soluble fertilizer, or organic alternatives like fish emulsion or seaweed extract.
- Frequency: Fertilize every 2-3 weeks, or as directed on the fertilizer packaging.
- Fertilizer Type: Use a water-soluble fertilizer, or organic alternatives like fish emulsion or seaweed extract.
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Air Circulation:Ensure good air circulation around seedlings to prevent fungal diseases and promote strong growth.
- Air Circulation Methods: Use a small fan to gently circulate air, or place seedlings in a well-ventilated area.
- Air Circulation Methods: Use a small fan to gently circulate air, or place seedlings in a well-ventilated area.
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Soil:Use a well-draining, nutrient-rich potting mix specifically formulated for seedlings.
- Soil Composition: Avoid using heavy clay soil, which can become waterlogged and harm seedlings.
- Soil Composition: Avoid using heavy clay soil, which can become waterlogged and harm seedlings.
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Pest and Disease Control:Regularly inspect seedlings for pests and diseases, and take appropriate action if needed.
- Pest Control: Use organic pest control methods, such as insecticidal soap or neem oil.
- Disease Control: Ensure good air circulation and avoid overwatering to prevent fungal diseases.
- Pest Control: Use organic pest control methods, such as insecticidal soap or neem oil.
Which nutrient is best for seedlings?
The most reliable plant nutrients for seedlings are SuperThrive and Botanica’s Grow formula. SuperThrive is a good all-round formula that is good for plants at any stage. Grow will help establish the stalks and leaves faster. Both will need to be diluted beyond their usual amount until a sprout is well-established.
Do seeds need fertilizer?
The seeds do not actually need fertilizer for the first few weeks of their life. It would be a seed sowing mistake to feed too early as germination can actually be hindered if there is too much fertilizer in the soil. It is always recommended to hold off applying fertilizer until the seedlings have developed their true leaves.
Should you feed seedlings fertilizer?
To grow strong and healthy plants from seed, whether they are flowers, vegetables, or shrubs, it is important to understand a plant fertilizer label and appreciate when the best time is to apply feed to seedlings. It can be a fine art, as you can harm your plants if you feed too early or over-fertilize.
How do I choose a good fertilizer?
Look for an all-purpose fertilizer that contains an even balance of nitrogen (N) to phophorous (P) to potassium (K). An all-purpose fertilizer will help young plants develop a sturdy root system and lush, healthy leaves.
What type of liquid fertilizer should I give my seedlings?
But, and this is key, you have to be very careful what type of liquid fertilizer you give your young seedlings – especially when it comes to the overall strength and consistency of the dose. There are three great options for fertilizing young plants. The first is to use all-natural compost tea. The second is to use all-natural worm casting tea.