How to Amend Your Vegetable Garden Soil

Broadforking Garden Bed with Fertilizer Amendments
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Last Updated on 2 years by Michelle

Those people who know how to amend garden soil will have more harvest than they know what to do with.

Have you ever wondered why some gardens are so much more productive than others?

There are many factors that contribute to soil quality, but the decision to amend garden soil is probably the most important.

Soil amendments can help improve pH levels, increase nutrient content, reduce soil compaction, and improve drainage.

If you want your vegetable garden soil to be rich in nutrients and healthy for your plants to grow in, then it’s essential that you know how to amend it, and amend it regularly.

This graphic shows the three components of great soil

How do you know when your soil needs to be amended?

You might suspect that it’s time to amend garden soil if you notice that your harvests are getting smaller and smaller over time.

Or, you may be starting from scratch and don’t know anything about your soil. Either way, starting with a soil test is the best and only way to know EXACTLY what your soil needs.

You can purchase soil test kits, and some states like North Carolina even offer soil testing for free.

Contact your local agricultural extension office to find out what’s available in your area.

To complete the soil test, you take samples of your garden soil in various areas of your raised garden beds or in-ground garden.

You’ll want to go deep into the soil, mixing the top 6-10 inches of soil to create your soil sample.

 

My soil needs amending. Now what?

If your soil test reveals that your soil is deficient in certain nutrients, you can amend the garden soil with organic fertilizers.

Nitrogen, phosphorus, and potassium (NPK) are the three primary nutrients that plants need to grow healthy and strong. The secondary nutrients that you’ll also sometimes see listed are Calcium (Ca) and Magnesium (Mg).

Some fertilizers boost one of the nutrients, while some fertilizers boost all three nutrients. Your soil test results will guide you as to which fertilizers to choose.

You can buy organic fertilizers that are specifically formulated for vegetable gardens, or you can use a general all-purpose organic fertilizer.

I use and recommend Espoma Garden tone, which is a general fertilizer (3-4-4). Click here to check the current price on Amazon.

If soil compaction is a problem in your garden, you can add organic matter to improve soil drainage and air circulation.

Compacted soil doesn’t allow water or oxygen to permeate the soil easily, which can lead to poor plant growth even when adequate nutrients are present in the soil.

This type of amendment also improves sandy soil structure by increasing the soil’s ability to retain water and nutrients.

If you live in an area that experiences a lot of rainfall, soil drainage may be a problem for you. In this case, amending the soil can also help to improve soil drainage.

If you are harvesting crops from your garden space on a regular basis, you will need to add back the nutrients that the plants are pulling out of the soil. Certain crops are heavy feeders (like onions, potatoes, and tomatoes, and other) and the organic materials in the soil will be severely depleted over time when you grow these crops over and over again.

How Do You Decide Which Amendments to Use?

Depending on what soil problems you’re experiencing, there are several different soil amendments that can be used to remedy the situation.

Amend Garden Soil for Improving soil pH levels

For improving soil pH levels, adding garden lime or wood ash is commonly recommended by gardeners. Either of these products will raise soil pH levels and make your soil more alkaline. To reduce the pH, use elemental sulfur or soil sulfur. Sulfur does the opposite of what lime and wood ash does, by lowering soil pH levels to make your soil more acidic.

Your soil test will give you an indication of how much your soil’s pH may need to be altered to get it in the range you want. Most garden crops and vegetables thrive between a pH of 6.0-7.0.

How Can You Add Nitrogen to Your Soil?

Adding nitrogen to soil is a great way to improve soil fertility and boost plant growth. Since plants need lots of nitrogen in order to grow sufficient leaf and plant structures, adding it as an amendment will increase the nutrients available for your vegetable plants. If you’re wondering how to add nitrogen into soil naturally, there are several different options that can be used depending on what type of soil you have.

Several amendments can be used to add primarily Nitrogen to your soil if you generally have enough Phosphorus and Potassium:

  • urea (46-0-0)
  • alfalfa meal (3-1-2)
  • feather meal (12-0-0)
  • blood meal (12-1.5-0.5)

How Can You Add Phosphorus to Your Soil?

Similar to nitrogen, phosphorus is an essential nutrient for plants that needs to be added to soil in order for vegetables to grow properly. Where nitrogen facilitates green leaf development and vigor, Phosphorus stimulates root growth, stimulates blooming and fruiting, and can foster plant maturity.

There are several ways you can add phosphorus naturally into soil. Bone meal or rock phosphate are two excellent types organic fertilizers that help add phosphorus to your soil.

Both of these types will provide your plants with the necessary nutrients including phosphorus as they break down over time.

Using Bonide Triple Phosphate 0-45-0 fertilizer is also a great way to add a hit of phosphorus to your garden soil. Click here to check current pricing from Amazon.

How Can You Add Potassium to Your Soil?

Potassium is the 3rd macronutrient that is absolutely critical to a successful harvest. Potassium is removed from the soil when crops are harvested, so it must be replaced. It is called potash because it used to be produced by leaching wood ash in pots.

A great option for an organic fertilizer that is high in potassium is Organic Kelp Fertilizer.

How Can You Add Organic Matter to Your Soil?

Now that we’ve covered the macronutrients NPK, we need to talk about organic matter. Having the right pH and balanced macronutrients is wonderful, but if water runs right off the soil surface without soaking into the soil, those nutrients simply won’t get into the plants where you need them. Breaking up the soil structure to create pockets were water can absorb, oxygen can flow, and roots can grow is essential for healthy plants.

Adding organic materials can be done in several different ways, with adding compost being one of the most popular options. Composted material gives you a double benefit, because it contains nutrients that are essential for plants as well as organic matter which helps to improve soil structure and drainage.

Compost, Leaf Mulch, and Grass Clippings

If soil compaction is a problem, then organic matter will help to improve drainage and soil aeration. Materials like leaf mulch and grass clippings can also make good soil amendments for this purpose because they provide excellent drainage in addition to improving soil structure by increasing water retention in the soil.

Starting a compost pile at home is relatively straightforward and there are a ton of resources you can look into to teach you how to start one.

If you’re not able to compost on your own, you can also purchase compost from a local garden center or nursery.

Alternatively, you can also add leaf mulch to your soil which will help to break down over time and provide the same benefits as compost.

Wood Chips as a Soil Amendment

Some people add broken-down wood chips into their garden beds to boost the organic matter. I’m doing this myself, but I don’t have results to share yet. It takes around two years for wood chips to break down enough to be added to your soil. I take new wood chips and shovel them into my pathways between each row. The chips will stay in the pathways and break down in the elements for two years, then I’ll shovel them into the garden bed as a soil amendment. The wood chips that are in my garden now have one more year to break down before I incorporate them into the soil and start the process over again.

How Much Soil Amendment Should You Use?

When it comes to soil amendments for vegetable gardens, a little bit goes a long way. In the case of compost or leaf mulch, you only need to add a few inches of amendment to the soil in order to see results.

However, if your soil is especially poor or lacking in nutrients, you may need to apply more. Test your soil, then add the appropriate amendments per the results. Wait a few months for the amendments to sufficiently break down into the soil, and test again. Once your garden soil is testing within the limits you want, you’ll just maintain that by adding amendments and organic fertilizers a couple times per year.

It’s important to note that soil amendments for vegetable gardens don’t last forever. Over time, organic matter will break down and release its nutrients into the soil which means you’ll need to add more to boost your soil’s fertility.

How to amend clay soil

Clay soil is one of the most difficult types of soil to work with since it’s naturally hard and dense. Root growth can be very slow in clay soil, leading to smaller harvests. In addition, unamended clay soil doesn’t usually drain well which can lead to waterlogged soil and root rot. However, properly amended clay soil is some of the best soil you can have because it holds on to nutrients extremely well.

One of the best ways to amend clay is by adding organic matter such as compost, manure, or leaf mulch. This will help to improve soil structure over time and provide essential nutrients for plant growth. You could also add in sand to help with soil drainage, but I don’t recommend it. If you only add sand to clay soil and nothing else, you’ll basically turn your clay soil into what amounts to concrete.

How to amend sandy soil

Sandy soil doesn’t hold nutrients very well which means they tend to leach out of the soil. In addition, sandy soil doesn’t retain water well which can cause plants to dry out.

One of the best ways to amend this type of soil is by adding organic matter such as compost or leaf mulch. These will help improve soil structure and drainage while also boosting fertility levels over time.

How to use cover crops to add nutrients to your soil

One way to add nutrients back into your vegetable garden soil is by using cover crops. These are plants that are grown specifically for the purpose of adding organic matter and nutrients back into the soil. There are several different types of cover crops, but some of the most popular ones include clover, buckwheat, and alfalfa.

Cover crops are grown for a season, cut back, and then tilled into the soil to add all the cover crop nutrients right back into the soil.

What happens if you don’t amend your soil?

If you don’t amend your soil, the nutrients in the soil will be used up by your garden plants and there won’t be anything left to fertilize new plants. This means that if you plant another vegetable crop after harvesting all of them, it’s not likely to produce much fruit or vegetables.

This is why soil amendment for vegetable gardens is so important. Planting beautiful transplants into poor soil is such a waste and it can put beginners off of gardening completely. Oftentimes new gardeners

How often do you need to amend your garden soil?

You may not need to amend your soil every year, but you should do it at least every two years. This will help keep your soil healthy and fertile so that you can continue to get big harvests from your vegetable garden. Ultimately, you’ll need another soil test to see how your nutrients are being used over time. Think of fertilizing and adding amendments as a “tune up” for your garden.

My exact process for amending my garden soil

So far, we’ve talked a lot about the general principles of how to amend with fertilizers and other soil amendments, but now I want to focus on what I do in MY garden space. I’m not an expert in what everyone else does when it comes to fertilizing and amending soil, but I’m an expert at what I do in my space.

My general amendment schedule

I’ve been incredibly successful growing in my zone 7B/8A clay soil, mainly because I work to increase the soil’s drainage and work to keep nutrients available and accessible.

My soil test results showed that I don’t need to worry about actively trying to change my pH, so I skip that part. I increase soil drainage by adding 2-3 inches of decayed leaf mulch every April and October. At the same time, I sprinkle 1/2 gallon of pelletized chicken manure to every 30″ x 20′ garden bed. I then broadfork all that into the top 6-8 inches of soil. That’s all I do for the general treatment of the soil. I make further amendments at the transplant planting stage.

Here you can see a dump truck load of leaf mulch (Black Gold) from Keep Gastonia Beautiful, our leaf mulch source:

 

Here are some examples of the routine garden soil amendment I described above. On the beds to the left you can see the pelletized chicken manure I’ve scattered over the leaf mulch. The bed in the middle is being broadforked to incorporate the amendments, and the bed on the right has been amended and broadforked.

Broadforking Garden Bed with Fertilizer Amendments

My transplant amendment schedule

I start all the plants that I can from seed and I grow year-round, so I transplant hundreds of plants into my garden soil every year. Every time I plant a transplant into the ground I put the following into the planting hole:

  • a handful of Vermisterra worm castings (yes, worm poop!)
  • about a tablespoon of Biotone Gardentone 3-4-4 organic fertilizer

I thoroughly mix those two together with about 2-3 inches of the soil in the bottom of the planting hole, then I plant, backfill with soil, and water everything in.

This mixture is absolutely amazing for supporting healthy plants and helping to ensure healthy plants and a nice harvest, as you can see:

Special considerations for fertilizing container gardens

This post has focused on in-ground garden beds so far, but I have to include container gardens as well, because they carry their own set of considerations that are different from other garden soils.

Containers hold a specific amount of soil, and that soil leaches nutrients much faster than the soil in garden beds. Fertilizers and amendments must be added back on a near-monthly basis.

Organic general-purpose vegetable garden fertilizers are best for those containers filled with potting soil. Organic fertilizers slowly release the nutrients into the soil, and generally take about a month to fully release the nutrients. By putting your containers on a monthly fertilization schedule, you ensure that your harvests are the best they can be.

Conclusion

It’s important to remember that soil quality is an ongoing process and requires regular care. If you want your vegetable garden soil to be rich in nutrients and healthy for your plants to grow, then it’s essential that you know how to amend it, and amend it regularly!

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