Can You Plant Directly into Compost? (Is It Safe for Plants?)

All that glitters is not gold. And all that doesn’t glitter is ‘black gold.’ Our black gold is the compost we have been using as a soil amendment for ages. It is called so because it provides our plants with nutrient-rich meals and makes them thrive.

But, of course, there’s nothing like too much when it comes to something we like, right? But is it the case with our plants? Do they want too much compost? Can you plant directly into compost? Let’s dig in!

Yes, you can plant directly into compost; however, it is not recommended as it will lead to excess drainage, structural instability, and overloading of certain nutrients. Instead, use it with soil to get the best results. Apply 1-2 inches of compost and topsoil, or use it as a mulch.

But what exactly is this compost we’re talking about? And how to use it to maintain plant health and reap the benefits?

What is Compost?

Compost is the ultimate product obtained from decomposing plants and food waste and is used to strengthen the soil. It is a valuable amendment that significantly improves poor soil and plant health by providing vital nutrients to growing plants.

So, if compost is this useful, why not use it as the sole growing medium for your plants? The idea is to give your plants everything they need in a reasonable amount, but is the approach we’re looking forward to beneficial for your plants in the long run?

Can You Grow Plants in Compost Only?

Yes, you can grow plants in compost only, but you should not. Being a powerpack of nutrients, compost might seem a perfect medium for plants to grow, but it is not advised to use it as a sole medium due to the following reasons:

Growing Plants in Compost Only
  • Excessive drainage: One of the primary purposes of adding compost to the soil is to facilitate drainage. But when there’s no soil, only drainage is left. Therefore, planting directly in compost will lead to excessive drainage and no water retention, no matter how good quality compost you use.
  • Lack of Structural Support: Soil provides the fundamental support to plants, while compost doesn’t. Planting in only compost will make plants unable to stand upright due to weak soil structure, even if they manage to grow somehow. Soil provides the perfect medium for plants to grow with a strong foundation.
  • Overloading of Nutrients: Especially in flowers, planting in compost leads to a surfeit supply of nutrients, particularly magnesium, potassium, and nitrogen. This leads to the redundant availability and overloading of nutrients.
  • Inadequate Moisture: Plants will become deprived of water due to excessive compost drainage, therefore, not fulfilling the essential requirement.
  • Compaction: Adding water to the compost leads to the formation of clumps, which ultimately prompts shrinkage.
  • Element Toxicity: In the worst-case scenario, overloading of nutrients will lead to ammonia toxicity and a spike in salinity, eventually leading to plant necrosis.
  • Pathogen Attack: Insufficient heat in compost or immoderate soil temperatures might lead to the dwelling of specific fungal pathogens, causing damping-off or blight disease.

However, with numerous reasons not to plant directly into compost, some plants still manage to surprise us by finding a way to thrive just in compost.

Plants That Can Grow in Pure Compost

Despite the drawbacks of planting directly into compost, certain plants have found a way to grow in the not-so-desired medium. These plants are:

Growing Tomato Plant in Pure Compost
  • Tomato
  • Cucumber
  • Pumpkin
  • Zucchini
  • Spring Onion
  • Baby Carrot
  • Watermelon
  • Eggplant
  • Cauliflower
  • Cabbage

These plants have a relatively shorter lifespan than the rest and are particularly heavy feeders, making them a good choice for planting in compost only. They take up the nutrients impetuously before there is a reduction in compost volume.

Points to Remember Before Growing Plants Directly into Compost

Before planting directly into compost, make sure to keep these points in mind:

  • Prefer ground-hugging (low-growing) and lightweight plants.
  • Use compost to grow the plants that grow well in slightly acidic conditions.
  • Use mature compost since it will be biologically less active; therefore, less heat and more nitrogen for plants.
  • Use black and friable compost with a rich and earthy smell (depicts maturity).
  • Prefer plants with good heat tolerance.
  • Keep the compost adequately moist.
  • Keep checking and maintaining the soil pH as growing vegetables require a neutral pH (6-7).

Since you are now aware of the greens and the conditions required for growing in compost, it’s time to look into the methods of using compost.

Methods of Using Compost

Compost Used as Mulch

1. Compost as Sole Growing Medium: This way, it is not impossible to grow plants. However, using compost as a sole medium won’t give you the desired results and would require a lot of maintenance (considering the drainage, shrinkage, inadequate moisture, etc.).

Although possible, this method is not recommended since pure compost doesn’t have all the nutrients plants require to develop. So, instead of a blissful experience, it would rather be a struggle for plants.

2. Compost With Topsoil: Using compost with topsoil is an excellent option for plants. You need to mix 1-2 inches of compost with the topsoil, and you’re good to go! This way, plants will be happy, healthy, and have everything that initially compost lacked.

3. Compost Mixed With Soil: It’s all about balance when using compost with regular garden soil. For example, clay soil would require more drainage, while sandy soil would require more water retention. You can balance both cases with a suitable compost-to-soil ratio.

4. Compost as Mulch: Compost is an outstanding alternative to dead leaves, straw, woodchips, and other traditional mulching materials. Add a 3-4 inch thick layer of compost around plants, and after some time, it will soak down into the ground, enriching the soil further. Unfinished compost can also be used as mulch.

5. Compost Tea: We like tea, and so do plants! Compost tea is a reinvigorating beverage for plants, and all you need to do is soak compost in water, and you’re all set! The fermentation process helps extract all the beneficial microorganisms from the compost in the water. So, don’t forget to treat your plants to a tea party!

So, you know everything about using compost for plants. But what about growing seeds with compost?

Can You Start Seeds in Compost?

Yes, you can use compost to start seeds, as long as the moisture conditions are appropriate. Initially, seeds take nutrients from within themselves to sprout. After that, roots gradually develop to seek nutrients from the growing medium.

Seedling in Fresh Compost

Essential Tips for Growing Seeds in Pure Compost

  • Prefer mature and finished compost with high humus content for starting seeds. Unfinished compost has phytotoxins which can hamper seed germination.
  • Ensure soil neither gets dry nor gets water-logged in the compost bin.
  • Plant the seeds at an appropriate depth and water thoroughly (just initially). You can also use diluted rice water for plants as a substitute in certain conditions. 
  • Avoid direct sunlight and excess watering until seedlings have germinated.
  • Avoid fertilizing until germination takes place.

Note: You can grow seeds directly in compost in containers. Take a small container, fill it with compost and dig in the seeds. This container gardening is easy and manageable. Remember, it is best to transplant seedlings to a favorable soil (mixture of soil and compost) after germination.

Since seeds germinate perfectly in compost, what else can be done? What about the raised garden bed?

Can You Fill Raised Beds With Compost Alone?

No, filling raised beds with compost is not a good idea. This is because of similar reasons like drainage, shrinkage, etc. Instead, a good raised bed should contain a blend of soil and compost, having only 30-40% compost. This is the ideal composition of compost in raised beds. 

Therefore, it is clear that plants don’t necessarily need ample nutrients. They just need them in the right amount, so much that the soil is favorable for them.

What Precisely Favorable Soil Means?

Favorable soil is particularly the one with all the essential nutrients in the right proportions and a good amount of compost. But what is a good amount when it comes to adding compost to the soil? How much compost is enough for plants?

Components for plant growth include:

  • Minerals: Plants need minerals majorly. They need around 45% of minerals to survive, readily available in the soil. Planting directly into compost would make plants devoid of these essential minerals.
  • Water: Plants need 25% of water to survive. This is where drainage and water retention capacity come into action.
  • Aeration: Like water, plants need 25% air (comprising all the essential gases) to grow. Aeration is maintained by turning over the topsoil and other methods.
  • Organic Matter: Plants need only 5% of this vitally important component, which they receive through compost. Surprising but true! However, this 5% aids in easing aeration, facilitating drainage, and maintaining water holding capacity. Compost also supplements the plants with beneficial nutrients.

Therefore, it is better not to plant directly into compost and only have a small amount of compost mixed in the soil, as an excess of everything is bad!

Can too much compost hurt plants?

Yes, too much compost can hurt plants. It can lead to drainage problems, making the plants thirsty. Moreover, excess compost won’t give the foundation to anchor the plant roots.

Does the compost pile turn into soil?

The compost pile doesn’t turn into soil. Instead, it loses nutrients through time, so mixing it with existing soil for plants to grow is essential.

Can I use compost as topsoil?

Yes, you can use compost as topsoil, provided it is backed up in the ground by existing topsoil. The compost applied to the topsoil leads to improvement and can help plants grow well. Apply 1-2 inches of compost, followed by topsoil, and your plants are good to go!

How long does compost last in soil?

Compost lasts from a few months to a few years, depending on the type of compost used. Homemade compost can last longer than store-bought compost since you can add decomposing material, like vegetable scraps, grass clippings, etc., to increase nutrient content.

Can you use compost as the sole medium for planting a vegetable garden?

Compost is a soil amendment and should be added to the soil in a limited amount because that’s what it is – an amendment. However, it is best to avoid using compost as the sole medium for planting as it helps improve the soil and leaves the soil and plants deprived of nutrients.

Can you plant indoor plants directly in compost?

Yes, but for best plant health, it is recommended to use garden soil with compost as potting soil. This potting mix would give better results than just using compost as potting soil.

Are manure and compost the same?

Manure, as well as compost, are soil amendments. However, fresh manure is primarily animal feces, while compost is decomposed organic material.

Can you grow plants directly into vermicast?

You can grow plants into vermicast, but it is not suggested. Vermicompost is also a form of soil amendment and cannot be substituted for soil.

Now you know what’s best for your plants and, more importantly, how much is best for your plants. You can now figure out what to do with that compost heap in your backyard. So let’s take that valuable treasure, black gold, and make the best use of it.

And, once you’ve rooted your precious plant in a good potting mix, you need to water it regularly. But, is water the only thing that can be used to water plants? Can you use milk instead? And is milk good for plants? Get all your answers with us.