Should I Fertilize My Vegetable Garden?

Fertilizing your vegetable garden can encourage plant growth and improve your yields. Unfortunately, it’s not as simple as dumping a bag into the soil for magic results. When used improperly, fertilizer can have negative effects on your plants, garden, and the surrounding environment. 

In this blog, we’ll talk about why you may or may not want to use fertilizer in your vegetable garden and how to do so efficiently. We’ll also include a few alternatives.

Always Get a Soil Test

Before you add any amendment to the garden, the best thing you can do is get a soil test. A soil test gives you information about the micro and macronutrients in your garden and your soil pH. This baseline will allow you to choose an appropriate fertilizer.

You don’t want to add fertilizer without testing. If nutrients are already present in your soil in good quantities, adding fertilizer will do more harm than good. Excess nutrients can inhibit plant growth, contribute to pest and disease issues, and reduce your yield. 

Excess nutrients also often run off with rain and irrigation. These nutrients wash into ditches, streams, and eventually other waterways where they can cause dangerous algal blooms. 

What Fertilizer Should I Use?

There is a wide range of fertilizers available to home gardens and knowing which one to select can be tough. Here are a few considerations to make the right choice for your vegetable garden. 

Organic Versus Synthetic Fertilizer

Two main categories of fertilizer are organic and synthetic.

Organic Fertilizer

Organic fertilizers are those derived from natural sources like plant or animal material. You may see organic fertilizers like kelp (a type of seaweed) meal or bone meal. Organic fertilizers are generally available in granules and slowly break down and release into the soil. 

This can be a disadvantage for plants that need a quick boost. However, organic fertilizers are less likely to create nutrient run off. They also can improve soil structure, feed beneficial microbes, and don’t form a crust on the soil like synthetic fertilizers may create.

When looking for organic fertilizer, the Organic Materials Review Institute (OMRI) seal indicates the product can be used on certified organic farms.

Synthetic Fertilizer

Also known as inorganic or chemical fertilizers, these are also derived from natural sources but have been processed and concentrated. Most of these fertilizers are quick-release and water-soluble, meaning that they’re quickly accessible to the plant. However, some are coated to slow the release. 

These fertilizers are immediately available to a plant that needs a quick boost. However, this means that it’s also easy to over-fertilize or burn your plants with them. As they’re water soluble and quick release, these synthetic fertilizers are also much more likely to end up in waterways. 

N-P-K

Beyond synthetic and organic, all fertilizers are marked with three numbers like 4-6-2 or 4-4-4. These numbers refer to key plant macronutrients, Nitrogen (N), Phosphorus (P), and Potassium (K). The number shows the percent of the bag’s weight that the nutrient makes up.

If you don’t know what ratio your crop needs, no worries. Most companies market their products for specific applications. You can find general fertilizers for vegetable or flower gardens or more specific ones like those for blueberries or tomatoes. If you’re still unsure, you can also Google your crop’s specific needs. trellisted cucurbits, melons, watermelons, edamame, southern peas, potomac corn,

What Plants Should I Fertilize

If you’re going to use fertilizer, it’s best to focus on “heavy feeder” crops that pull a lot of nutrients from the soil. These include: 

  • Tomatoes
  • Peppers
  • Eggplants
  • Sweet Corn
  • Squash
  • Cucumbers
  • Potatoes
  • Cabbage
  • Broccoli

What Plants Don’t Benefit from High-Nitrogen

Nitrogen is essential for plants’ vegetative growth, but some plants need less and are more sensitive to over-fertilizing. These include:

  • Root Vegetables (beets, carrots, radishes)
  • Legumes (beans, peas, cowpeas)
  • Leafy Greens (lettuce, collards, spinach)
  • Sweet Potatoes

In high nitrogen soil, root vegetables like beets and tubers like sweet potatoes tend to put on excellent foliar growth at the expense of root and tuber development. This can lead to a smaller harvest or impact quality, leading to roots that are less sweet and nutrient-rich.

Legumes like cowpeas, pole beans, and snap peas all fix nitrogen on their own. They have a symbiotic relationship with bacteria on their root nodes that allow them to covert atmospheric nitrogen into a usable form. Excessive nitrogen caused by over-fertilization can hinder this process and negatively affect the plants’ health. Excess nitrogen may also increase foliage growth and reduce fruit growth. 

When you over-fertilize leafy greens, the plants may put on poor root growth and bolt early, shortening your harvest window. 

This is not to say that these plants don’t benefit from fertilizer, just that you need to be careful with the ratio as they’re sensitive to high nitrogen. 

Different plants require nutrients in different rations. For example, beets, carrots, turnips, and other root vegetables thrive with plenty of phosphorous, which is essential for root development. 

When Should I Fertilize?

For most annual vegetable garden crops, agriculture experts recommend applying granular fertilizer in spring, just before planting. You can incorporate this into the soil and then water it.

Heavy feeders like corn, squash, and tomatoes may also benefit from “side-dressing” or an additional application of fertilizer later in the summer. For corn, side-dress when the plants reach 12 to 24 inches tall. Fruiting plants like tomatoes and squash can benefit from a low nitrogen fertilizer once they begin to flower. Adequate quantities of phosphorous and potassium are ideal for fruit production. 

When applying fertilizer, be sure to follow the product’s instructions. There should be application rates on the package, often indicating how much to apply per thousand feet of garden area. Extension agents or nursery staff can help you work out how much you need for your space if you’re unsure. 

Other Ways to Add Nutrients to Your Garden

Many organic gardeners choose to forgo fertilizer entirely. For some, it isn’t worth the cost and risks. Thankfully, there are plenty of other ways to add nutrients to your garden:

Beneficial Insects: 4 Ways to Attract Lacewings

Lacewings are one of our favorite beneficial insects to find in the garden! Their shimmery wings and slender body make them look a bit like mini nocturnal dragonflies. While they don’t get the credit that lady beetles, bees, and butterflies often receive, these delicate insects are among the gardener’s best helpmates.Green adult lacewing on a pink and yellow flower

Why are Lacewings Good for the Garden?

Lacewing larvae, or the immature stage of lacewings, are voracious predators. They feed on a wide range of garden pests including aphids, mealybugs, some scales, lace bugs, asparagus beetle larvae, Colorado potato beetle larvae, and caterpillar eggs and larvae including corn earworms, cabbage loopers, and cabbage worms.

Lady beetles usually take the spotlight for killing aphids, but lacewings are actually more effective. These talented predators feed on a wider range of insects. According to some sources, lacewing larvae can eat about ten times the number of insects as lady beetles. A single lacewing larvae can eat about 200 aphids in one week. 

Lacewings also make sustainable pest control because they stay in areas that they find suitable habitat and food. We’ll cover how to attract them below.

What Lacewings Will I Find?

There are over 4,000 species of lacewing worldwide, with 85 to 90 of these species being native to the United States! The most common species to see in the Southeastern United States where we grow, are from a large family called the green lacewings (Chrysopa spp.).

However, it’s also possible to find other species like the brown lacewing (Hemerobius costalis). Thankfully, all the species of lacewing are easy to recognize as lacewings and beneficial for the garden.

Lacewing Eggs Left (Fritz Geller-Grimm, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons)
Lacewing Larva Eating Aphid Right (Eric Steinert, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons)

How to Identify Lacewings

As adults, lacewings are nocturnal and you may find them on your window screens of around outdoor lights. They have long, slender, soft bodies that are usually green or brown. Their name is fitting and their shiny, translucent wings are netted with veins. They also feature long, slender antennae and may have gold, coppery. or dark eyes. 

Their eggs are small, about 1mm in length and typically white. They lay their eggs atop thin, hair-like filaments. 

The eggs hatch into the larval stage. In this stage, the lacewings lack wings and have a flattened alligator-like body with distinct legs. Some species collect organic debris on their hairs to deter predators.

Before maturing into adults, the larvae pupate in silk cocoons on the underside of leaves and stems.

Lacewing larva covered with sand grains on a leaf
Larva of unknown species camouflaged with sand grains. Sanja565658, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Four Ways to Attract Lacewings to Your Garden

Lacewings are beautiful to see and helpful for controlling pests. Creating a suitable habitat for them in all their different life stages is essential to encouraging them to live in your garden.

Plant Pollen-Rich Flowers

Adult lacewings make the switch to a vegetarian diet, feasting on pollen and nectar. While they may not be helpful as predators in this stage, offering them plenty of food usually means that they’ll stick around to lay some eggs, providing your with another generation of lacewings. 

They prefer small flowers that are rich in pollen and nectar like goldenrod, Queen Anne’s lace, Dara, dill, cosmos, coreopsis, caraway, tansy, Angelica, alyssum, and fennel. 

Lacewings have multiple generations per year that need to feed on pollen and nectar to reproduce. Having flowers blooming throughout the season is key. Planning successions and opting for long blooming flowers can make a big difference. Green adult lacewing on a pink flower

Provide Shelter

Depending on the species, lacewings overwinter in protected spots as adults or larvae. Shrubs, hedges, and dense foliage near your garden can provide suitable shelter. Adults may also choose to hunker down in dead plant material and leafy debris, so waiting until it’s warm in spring to do your garden clean up can also help keep them safe. 

Reduce Chemicals in Your Area

Pesticide applications will kill lacewings and other beneficial insects. Avoid using pesticides, especially broad-spectrum on your property. Where possible, encourage your neighbors to do the same. 

Note that pesticides may also come in on flowers and nursery plants. When possible buy local, ask about treatments, or grow your own starts at home. 

Allow Some Early Aphids

This may seem like a silly idea, but an early population of pests like aphids can help ensure lacewings find your garden in the spring. If you have some early aphids, wait a bit to remove them if possible. 

Purchasing Lacewings

While most people choose to attract native lacewings, some farmers and gardeners order them. Several green lacewing species like Chrysoperla rufilabris are now available online as a biological control for farms and orchards. 

Lacewings are an excellent part of the organic gardener’s integrated pest management plan. Attracting and encouraging local lacewing populations is a great way to keep several annoying garden pests in check without resorting to pesticides. 

Summer Cover Crops

Cover cropping is an incredibly beneficial practice for anyone who gardens. It helps improve the soil, protect the environment, attract pollinators, and so much more. Unfortunately, most gardeners think of cover cropping as a practice for the off season. However, summer cover crops have a lot of unique benefits and you can work them into your garden without giving up any production. 

Benefits of Summer Cover Crops

Summer cover crops can help improve your soil health and production during the season. They also help protect your garden and the environment in several essential ways.

Reduce erosion. Usually associated with fall and winter storms, erosion isn’t a major focus in summer, but it can happen any time of year. It’s a critical issue in the United States. Scientists estimate that we’ve lost 30% of our topsoil in the past 200 years. 

In summer, all it takes is a strong thunderstorm rolling through to wash away loose soil or drying winds picking up soil particles. You should never leave your soil bare. 

Erosion doesn’t just negatively affect your garden health, it has significant impacts on the ecosystem. Eroded sediment and nutrients end up in streams, rivers, and eventually the ocean, where they can cloud waters and cause toxic algae blooms.

Having cover crops on the soil also allows for better water infiltration and soil structure which can help you create a more drought resistant garden. 

Suppress weeds. Weeds are at their most aggressive in summer, which is why it’s a key time to get ahead of them with cover crops. Quick growing cover crops can crowd out and shade weeds, suppressing them for later vegetable crops. 

Some cover crops like buckwheat and sorghum sudangrass also release chemicals to prevent the germination or growth of weed in a phenomenon called allelopathy.

You can also kill the cover crops through rolling or mulching and leave them on the surface as mulch. Then transplant crops into the mulched bed. The mulch will continue suppressing weeds as it breaks down.

Attract beneficial wildlife and insects. Beneficial animals and insects are some of the gardener’s best allies. Some like hummingbirds, flies, bees, and butterflies pollinate crops. Others like swallows, bluebirds, toads, wasps, lady beetles, lacewings, and wheel bugs feed on common garden pests, keeping their populations low. A few, like earthworms, millipedes, and pill bugs, help break down organic matter, improving soil structure. 

None of these animals or insects thrive in areas with bare soil. Sowing cover crops provides cover and food sources. Some cover crops like buckwheat and hairy vetch also have flowers that may help attract predatory wasps, bees, and other pollinators. 

Fix nitrogen. Certain cover crops are nitrogen fixers. These plants have a symbiotic relationship with specific bacteria. The bacteria colonize the plant’s roots and pull nitrogen out of the atmosphere. The bacteria use the nitrogen and then it becomes available to the plant.

These nitrogen-fixing plants include a few summer cover crops like southern peas, soybeans, buckwheat, sunn hemp, and hairy vetch. 

To make the nitrogen available to your next crop, the cover crop needs to die and decompose. Depending on the crop, you can kill it by cutting it, tilling it under, tarping it, or waiting for frost to kill it in the fall.

Add organic matter. Fast-growing summer cover crops are a great way to add tons of biomass to the soil. As they break down, they add organic matter, which improves soil structure, increases water infiltration, provides nutrients, and increases microbial and beneficial insect activity. 

Impact plant diseases. In some cases, summer cover crops may help disrupt disease cycles in the garden. Some research has shown reductions in blight in no-till, cover crop gardens. Pearl Millet Summer Cover Crop

How to Work Summer Cover Crops into Your Garden Plan

You don’t need to give up production to grow summer cover crops! There are several ways you can squeeze cover crops into the summer garden without sacrificing your vegetables.

Use pathways. If your garden has pathway space, you can take advantage of it by sowing it in a cover crop like white clover which will tolerate some traffic. You can mow the paths and apply it as mulch under other crops.

Interplant. You can also interplant cover crops. Strips of clover, vetch, and other cover crop can have amazing benefits. According to the North Carolina State Extension, “research in Georgia reported high densities of big-eyed bugs, lady bugs, and other beneficial insects in vetches and clovers.” They also found that, “assassin bugs have destroyed Colorado Potato Beetle feeding on eggplant planted into strip-tilled crimson clover.”

You can grow some cover crops in between other crops. Plant soy beans or southern peas beneath tall crops like corn or sunflowers. You can also grow fast-growing cover crops like buckwheat between hills of vining crops like winter squash or melons. Cut the buckwheat as the vine start to sprawl and use it as mulch. 

Pull unproductive crops immediately. If your lettuce has bolted, radishes have gone woody, or beans are slowing down, consider pulling them and sowing a summer cover crop. While letting lettuce flower and beans decompose naturally may provide some minor benefits, using a cover crop is a more productive use of the space. 

Beat the heat. In the Deep South, the hottest days of summer can limit vegetable production. Rather than fighting the heat to eek out more production, you may just want to avoid it. For some crops like brassicas, greens, bush beans, and cucumbers, you can get plenty of production in the early summer and fall.

Take well-earned breaks. If you find your garden is getting away from you and your summer is busier than expected, it may be worth sowing a cover crop rather than another succession. A cover crop will essentially take care of its self while improving your soil for another crop in the fall or next season. Sometimes this is more productive than sowing more beans, squash, or other vegetables you won’t have the time to weed, harvest, and preserve.

Buckwheat spring cover crops in bloom

How to Select a Summer Cover Crop

All summer cover crops have their pros and cons. What cover crop you should choose will be based on a few factors:

  • Time Available
    It’s easiest to choose and appropriate cover crop when you have a good garden plan. Maybe you want a heat tolerant cover crop to grow for 30 days in the middle of summer in between squash plantings. Buckwheat may work in this scenario. Maybe you have an empty bed 80 days before your first frost and want a cover crop that will die back and allow you to plant fall garlic. Sunn Hemp could be a good choice.
  • Frost Tolerance
    Some summer cover crops like buckwheat, are frost sensitive and will die with the first frost in fall. Others, like clover and oats, will continue to grow.
  • Nitrogen Fixation
    If your next crop is a heavy feeder like broccoli, corn, garlic, onions, or tomatoes, choosing a nitrogen fixer like sunn hemp, hairy vetch, clover, soy beans, or southern peas is a great option.
  • Biomass Production
    If adding organic matter to the soil is a priority, you’ll want to choose a cover crop that quickly puts on a lot of biomass. One of the best options is sunn hemp which can reach 6 feet tall in 60 days. Other good options include buckwheat, millet, sorghum sudangrass, vetch, oats, and barley.

Here are a few summer cover crops you may consider. Listed with each are some of their important features. 

Buckwheat

  • Blooms and is ready for incorporation in 30 to 45 days.
  • Fast growing.
  • Frost sensitive.  
  • Flowers attract bees and parasitic wasps. 
  • Tender stems are easy to cut down.
  • Deep root system is adept at mining subsurface minerals.

Pearl Millet

  • Ready for incorporation in 40 to 60 days.
  • Grows well in acidic soil and poor soil.
  • Thrives in warm climates.
  • Drought tolerant.
  • Excellent biomass producer growing 3 to 6 feet.
  • Frost sensitive.

Sunn Hemp

  • Ready for incorporation in 60 to 90 days.
  • Fast growing and excellent producer of organic matter (may reach 6 feet).
  • Nitrogen fixing.
  • Frost sensitive.
  • Suppresses nematodes.
  • Thrives in hot climates.
  • Tolerates drought.
  • Extract nutrients from deep within subsoil. 

Soy Beans

  • Ready for incorporation in 45 to 60 days.
  • Fast growing. 
  • Tolerates hot weather.
  • Nitrogen fixing.

Southern Peas

  • Ready for incorporation in 50 to 60 days.
  • Vigorous.
  • Drought tolerant.
  • Nitrogen fixing.
  • Sprawling vines.

Sorghum Sudangrass

  • Ready for incorporation in 60-70 days.
  • Suppresses weeds.
  • Suppresses nematodes.
  • Loosens subsoil and reduces compaction.
  • Excellent biomass producer growing 5 to 12 feet tall.
  • Provides habitat for beneficial insects like lacewings.
  • Requires a large mower and is tough to cut with hand tools. 

Oats 

  • Ideal for late summer and early fall planting.
  • Grows quickly.
  • Produces plenty of biomass or mulch.
  • Frost hardy.
  • Oats will get winter-killed when temperatures drop below 10°F.
  • In cold climates, it makes an excellent mulch for spring crops and in arm climates you can cut it in spring.

Barley

  • Ideal for late summer and early fall planting.
  • Frost hardy.
  • Drought tolerant. 
  • Barley will get winter-killed when temperatures drop below 17°F.
  • In cold climates, it makes an excellent mulch for spring crops and in warm climates you can cut it in spring.

Hairy Vetch

  • Ideal sowing period from August 1st to November 1st. 
  • Highly efficient as a nitrogen fixer, it’s recommended to wait until at least 50% of the plants have flowered before mowing the crop to maximize nitrogen fixation. 
  • In the spring, after flowering starts, mow the vetch and transplant tomatoes or other large plants directly into it, or till it under.

Clover

  • Cold tolerant perennial.
  • Versatile and may be sown in winter, spring, late summer, or fall.
  • Excellent for suppressing weed growth.
  • Nitrogen fixing. 
  • Attracts beneficial insects.
  • Acts as a living mulch in paths or between rows.

Creating a sustainable, productive garden means that we’re focusing on soil health year round. As you plant and plan your garden this season, think about where you may be able to sneak in a few summer cover crops. 

Saving the Past for the Future