Your garden plants are most vigorous and productive when they have a steady supply of essential nutrients. Plants can extract some of their needs from healthy soil, but supplementing with fertilizer at key points through the season can dramatically improve their performance. The best garden fertilizers are designed for specific purposes. Keeping your plants well-fed is easy when you have handy products and a plan tailored to your needs and conditions. We’re here to help.
Vegetable Fertilizer Basics
Plants rely on three “macronutrients” to power their growth: nitrogen, phosphorus, and potassium. They are the key components of packaged fertilizers, identified on the label as N-P-K. They are all critical to plants’ health, each playing a different role.
Nitrogen (N) fuels the growth of leaves and stems, so it is especially important early in plants’ life cycle as they get established. It is the one nutrient that is naturally scarce in even fertile soil, so gardeners often need to supply it. Nitrogen-deficient plants grow slowly, have weak stems, and yellowing or discolored leaves from the tip inwards.
Phosphorus (P) supports healthy root development in young plants. Almost all garden plants benefit from supplemental phosphorus early in their growth, but root crops, such as carrots and turnips, especially depend on it. When deficient in phosphorus, leaves and stems may have a purple tint or be prone to wilting.
Potassium (K) promotes flower and fruit production, so it’s essential as the plant shifts into its reproductive phase. This nutrient also helps plants resist diseases. When potassium levels are too low, plants bear few flowers and set few, small fruit or vegetables. Curled or crinkled leaf edges that look dry are other signs of potassium deficiency.
Along with those major elements, your garden plants also need smaller amounts of key minerals, or micronutrients. These include calcium, zinc, copper, iron, boron, and manganese. Plants can extract them from the soil but if they are deficient, growth may be hindered. You may need to use supplements to bolster the amounts of these minerals.
When shopping for packaged fertilizers, you’ll see the N-P-K ratio listed on the label. These numbers represent the proportion of these elements in the product. Burpee Enhanced All-Purpose fertilizer is 5-5-5, so it has equal portions of all three macronutrients. Burpee Organic Tomato + Vegetable Granular Plant Food is 3-6-4, so it’s higher in phosphorus and potassium than nitrogen, making it a good choice for midseason feeding.
Organic vs. Synthetic
The nutrients in organic fertilizers come from naturally occurring sources, such as alfalfa meal, a high-nitrogen plant material. Organic fertilizers tend to come with a suite of micronutrients. They work best in soil that’s biologically active, with a robust population of microbes that break down the fertilizer into the nutrients in the form that plants’ roots have evolved to take up.
Synthetic fertilizers are manufactured from chemical elements, such as ammonia. They can be powerful and stimulate dramatic growth. Synthetic fertilizers usually contain only three out of 17 essential elements for plants, says Burpee horticultural expert Brie Zettl."This larger number of nutrients has been shown to result in better flavor and higher nutrient content in the food." What’s more, synthetic fertilizers don’t nourish the microbes in the soil that protect plants from soil-borne diseases.
How to Apply Vegetable Fertiliizer
Start with a test. Before you begin adding nutrients to your garden, take time to assess the content of your soil. The Deluxe Garden Soil Testing Kit shows you the amount of available nitrogen, phosphorus and potassium to nourish your plants. It also has tests for soil pH, which affects plants’ ability to take up those nutrients. You can get soil tests through your state’s extension service, too.
Before planting. If your soil test shows you need to add supplemental nutrients, you can add a balanced granular fertilizer such as Burpee Natural Organic All Purpose Granular Plant Food to the bed about a week or so before planting. Mix it into the top couple inches of soil and water lightly. The nutrients will be ready for uptake as soon as your plants start growing.
During the season. Give your plants a boost as they’re growing with either a granular or liquid fertilizer. To use a granular type, such as Burpee Organic Tomato + Vegetable Granular Plant Food 3-6-4, spread the fertilizer around the soil just below the outer canopy of the plant. This approach is known as side-dressing. Avoid putting fertilizer close to the stem, which may burn it. Remember to water after application, Zettl adds.
Liquid fertilizers, like Burpee’s Organic All-Purpose Water Soluble Plant Food, are mixed with water and sprinkled onto plants. Because they are already in liquid form, the nutrients are quickly absorbed. Just be sure to follow the dilution directions on the packaging so you don’t burn or overfeed the plants.
Your Fertilizer Schedule
Base level. Test your soil each season and add nutrients as indicated by the results. If the test shows you need to add nitrogen, for instance, but the other elements are abundant, use a nitrogen-rich plant food such as Burpee’s Natural Organic Blood Meal. When you need to bump up the phosphorus content, go with Burpee’s Natural Organic Bone Meal.
Steady growth. Crops such as sweet corn, broccoli, and cauliflower are heavy feeders, so they need fertilizing every other week. If you grow and harvest leaves from greens such as lettuce and spinach, treat them to Burpee’s Natural Organic Leafy Green and Herb Plant Food after each trimming to provide nutrients for continued production.
Fruit set. When plants such as tomatoes, peppers, and cucumbers begin to flower and set fruit, use Tomato and Vegetable Blossom Set Spray to promote more and healthier blooming.
Do's and Don'ts of Feeding Your Vegetable Garden
Fertilizers provide the resources your crops need to thrive, but they are most effective if you use them correctly. Remember these tips when feeding your vegetable garden.
DO
- Follow Directions: Read and adhere to the application instructions on the fertilizer packaging. While fertilizers are safe for your plants, when misapplied they can impede growth or cause other harm to plants.
- Spread Away: Take care to apply granular fertilizer away from plants’ stems so they are not burned or otherwise damaged.
- Water After: Granular fertilizers require water to begin to break down and release their nutrients. Always dampen the soil after applying.
- Diagnose Problems: If the leaves on your plants are yellow, wilted, spotted, or otherwise looking unhealthy, look up the symptoms in a reliable book or Website. The causes may be connected to a nutrient deficiency.
DON’T
- Skip The Test: A soil test is the only trustworthy way to determine what nutrients your garden needs. Applying fertilizer without a test can lead to imbalances in the soil that will hinder plants’ growth.
- Overfeed: Resist the temptation to overdo fertilizing. More is not better. As with people, overfeeding your plants can lead to unhealthy growth. Moreover, excess nitrogen in the soil can attract pests and promote plant diseases.
- Apply in Adverse Conditions: Plants are stressed during extreme weather such as a heatwave, cold spell, or extended drought. The stress inhibits their ability to take up nutrients. Wait to apply granular fertilizers until conditions return to normal.
- Choose Just Any Product: Not all plant foods are alike. The best garden fertilizers are formulated for specific purposes, so you want to use the right one for your garden’s needs and the plants’ life cycles. Using high-nitrogen fertilizer in the middle of the growing season, for instance, may lead to robust leaf and stem growth but reduce the fruit set.
Developing a fertilizer schedule increases your chances of success with vegetable gardening. Keep in mind what you learn from your soil test to determine just what your garden needs. Feed your crops regularly and they will have the nutrients they need to produce the healthy harvest you want.
See all your fertilizer options from the gardening pros at Burpee.
You nurtured seedlings all winter, transplanted them outdoors successfully and now, you're protecting them from pests, watering regularly and dutifully pulling weeds.
But there's one piece missing from your plant-care puzzle: fertilizer. When determining how to fertilize your vegetable garden, you'll need to develop a fertilizer calendar based on a variety of factors.
Not sure where to start? Here's exactly how to create a garden fertilizing schedule tailored to your plot's needs.
Vegetable Fertilizer Basics
Fertilizer can help boost your plants' bounty, but how does it work? In short, fertilizer replenishes and supplements soil with the nutrients your vegetables need to grow healthy roots, foliage and fruits.
Organic fertilizers consist of naturally occurring materials, while synthetic fertilizers contain manufactured materials. Synthetic fertilizers are available for plants to absorb more quickly because they're already in soluble form. Organic fertilizers, on the other hand, need soil bacteria and fungi to break them down into absorbable components. Synthetic fertilizers usually contain only three out of 17 essential elements for plants, whereas organic fertilizer usually contains all of them, says Burpee horticultural expert Brie Zettl."This larger number of nutrients has been shown to result in better flavor and higher nutrient content," she adds.
The numbers on each bag of fertilizer represent the percentage of nitrogen, phosphorus and potassium, or N-P-K, within. For example, 10-10-10 means the fertilizer contains 10% of each element. This balanced mix supports overall plant health. Nitrogen promotes leafy growth, which is why lawn fertilizers typically contain a larger percentage. Potassium encourages strong root development, while phosphorous helps flower and fruit production.
How to Apply Vegetable Fertilizer
First, perform a soil test to determine whether your garden truly needs fertilizer (more on that below). If your soil is lacking nutrients, then fertilizer or compost can be cultivated into the top several inches of soil. Prior to planting, Zettl recommends taking a gentle approach."Fertilizer can easily burn young plants, so I generally use organic matter, such as aged compost, to amend the soil before planting," she says.
Two to three weeks after planting, you can spread fertilizer around the soil just below the outer canopy of the plant. Do not put fertilizer near the stem, and remember to water after application, Zettl adds.
Before You Plant
Before you run to the garden center and fill your cart with fertilizer, take these crucial steps to set your garden up for success.
1. Perform a Soil Test
Send a soil sample to your local extension office for the most accurate, reliable results. It's virtually impossible to know how to fertilize your vegetable garden without first knowing your soil's pH and nutrient level. If you make an uneducated guess, you risk applying the wrong fertilizer, damaging your plants or spending money on products you don't need.
According to the University of New Hampshire Cooperative Extension, the optimal soil pH for vegetables falls between 6.5 and 6.8. Your test results should provide instructions on how to lower or raise your soil's pH, such as boosting pH levels with lime or lowering them with iron sulfate.
Before fertilizing, be sure you understand and adjust your soil's pH. Once your results fall in the vegetable pH sweet spot, you'll be ready to get fertilizing and planting.
Depending on where you live, your soil may already be garden-ready:"In some parts of the country — think soil enriched by volcanic eruptions in Washington state and Oregon, for example — potassium levels in the soil are already really high," Zettl says."Phosphorus levels are often adequate as well. You don't need to apply more with fertilizer, and if you do, you run the risk of killing your plants and the beneficial symbiotic organisms that help your plant feed. A good nitrogen-rich 5-1-1 fish fertilizer will work just fine in many cases."
2. Apply Mixed Fertilizer to Bare Soil
If this is your first year of vegetable gardening with fresh soil, you can usually skip this step. But, after a year or two, you'll most likely need to apply a vegetable fertilizer containing a mix of N, P and K according to package directions. Apply just before planting, or you run the risk of the nitrogen dissipating.
As You Plant
To help prevent transplant shock by strengthening roots as a whole, apply a potassium-rich fertilizer post-planting.
After You Plant
If your fertilizer is a solid like a granular or compost, always water after fertilizing to prevent burn, Zettl cautions. Once your plants are in the ground, it's time to focus on providing optimal nutrition for the remainder of the growing season. You can either follow a standardized schedule or customize your plan to maximize your specific plants' growth.
1. Follow a Simple Vegetable Garden Fertilizing Plan
As a general rule, fertilize right before planting, then again when plants flower or hit a growth spurt. Consider the crops you are growing and mark some dates on your calendar to remind you when it's time to feed, Zettl suggests."Some will be heavier feeders than others and your harvest will be improved if you know which crops those are in your garden," she says."For example, broccoli and cauliflower are notoriously hungry and will not form a crown if they aren't fed enough, whereas applying too much fertilizer to lettuce can cause leaves to become soft and more prone to rot."
2. Create a Custom Vegetable Fertilizer Schedule
If you want to fine-tune your fertilizing plan to ensure you deliver the right nutrients to the right plants at the right time, explore growing guides or research if any of your plants have particular fertilizer requirements. For example, tomatoes consume large amounts of calcium and often need supplementation throughout the growing season.
3. Look for Signs Your Plants Need a Boost
As the growing season progresses, look for signs your plants are weakening, such as drooping, wilting, stunted growth or a lack of fruiting. Rot at the bottom of tomato and pepper fruits (blossom end rot) means lack of calcium and magnesium. But before you fertilize, ensure there isn't another culprit at play, such as a lack of sunlight or water. Zettl says,"Plants that require full sun need at least six hours of direct light daily. Vegetables need 1 to 2 inches of water weekly. Use a rain gauge to measure how much you need to supplement what nature is already supplying."
4. Provide Supplemental Nitrogen as Needed
According to the University of Missouri Extension, some vegetables need a nitrogen boost through side-dressing as the growing season progresses. Nitrogen guidelines for common vegetables include:
- Asparagus: Very early spring, before growth emerges (around Valentine's Day in most places in the US)
- Cruciferous vegetables (such as broccoli, cabbage and cauliflower): Three weeks after transplanting seedlings, and every three weeks after that until they crown
- Cucumbers: One week after flowering
- Peas and beans: After the first set of pods
- Peppers and eggplants: After the first flowers emerge
- Sweet corn: When plants reach 8 to 10 inches tall, then again shortly after tassels appear
- Tomatoes: One to two weeks before you think the first tomato will ripen, plus two weeks after picking the first tomato for indeterminate cultivars
Do's and Don'ts of Fertilizing Your Vegetable Garden
Fertilizers can become too much of a good thing if misapplied. As you learn how to fertilize your vegetable garden, keep these tips in mind so you can give your plants what they need when they need it.
Do:
- Apply the correct amount — or even a bit less. Zettl recommends taking a cautious approach when it comes to measuring fertilizer:"More is never better," she says."Fertilizer companies tell you the maximum amount you can use before burning the plant — not the amount the plant actually needs and will use. Unused nitrogen attracts pests and disease."
- Apply fertilizer according to package directions, depending on the type of fertilizer you're using.
- Mix fertilizer in with your soil before planting if needed.
- Continue to check in on your plants throughout the growing season.
Don't:
- Apply fertilizer without a soil test.
- Apply fertilizer during a drought, heatwave or when plants are otherwise under stress, with the exception of seaweed-based fertilizers, which support drought-stricken plants.
- Use lawn fertilizer in your garden, as it contains too much nitrogen and will encourage foliage growth at the expense of fruit development.
Developing a fertilizer schedule is an essential part of your vegetable gardening success. With a bit of research and planning, you can create a calendar for fertilizer application that will help your plants stay strong, vigorous and productive.
To learn more about organic fertilizer and how to incorporate it into your garden's fertilizer schedule, see Burpee's organic fertilizer guide.