“I have some large compost bins, which produce a lot of compost. What kind of “dirt” with inorganic materials do I need to plant things in order to get the best results? How much inorganic material do I need? This question came from Naomi or Oakdale, California.
Answer: Congratulations on your composting success! Compost is one of the best garden amendments available. You can plant in compost by itself, but if you want to use it for container planting, I suggest mixing it with other things or adding it to your sandy garden soil.
Compost is the magical ingredient that improves all soils. Its nutrients feed plants while its organic matter creates a better structure for roots. But with its benefits, you may wonder – can I just plant directly into pure compost? Or should compost be mixed with native soil first?
There are good arguments on both sides of this debate, Below we’ll explore the pros and cons of planting in pure compost and offer some best practices on how to use it in your garden,
The Case For Pure Compost Planting
There are some compelling reasons why planting directly into pure compost can work well
1. Compost Has Excellent Drainage
Compost’s loose, crumbly texture allows for superb drainage. Plant roots thrive in compost’s air pockets and never sit in waterlogged soil.
2. Nutrients Are Easily Accessible
Pure compost surrounds roots with a feast of nutrients like nitrogen, phosphorus, and potassium that have already been broken down into plant-available forms.
3. It Fosters Beneficial Microbes
Billions of helpful microorganisms thrive in finished compost. These beneficial bacteria and fungi protect plant roots and aid their nutrient uptake.
4. Fewer Weeds
Quality compost lacks weed seeds and propagules that can plague gardens. Planting in pure compost gives crops a weed-free start.
Based on these advantages, planting directly into 100% compost can provide ideal conditions for plant growth.
Reasons For Mixing Compost With Soil
However, there are also good arguments for blending compost with native soil:
Water Retention Issues
Pure compost is quick to dry out and needs very frequent watering. When mixed with soil, compost can hold moisture better.
Nutrient Imbalances
Undiluted compost may contain extremely high levels of nutrients that can burn plant roots or leaves. Mixing moderates fertility.
Poor Structural Support
Roots need the firm support of soil particles to anchor and spread properly. Compost alone lacks this stability.
Few Microorganisms
While compost contains microbes, soil includes even more, especially beneficial mycorrhizal fungi. Blending the two inoculates compost with soil’s microbe diversity.
Expense
Compost is often more expensive than soil. Stretching it with native soil saves money.
For these reasons, many gardeners find a 50/50 blend of compost and topsoil provides the ideal balance of fertility, structure, and moisture retention.
Best Practices For Planting In Compost
When considering planting in pure compost versus amended soil, keep these tips in mind:
-
Test compost pH and nutrient levels first to check for imbalances. Adjust as needed.
-
For seeds, fill cells with a 50/50 mix of compost and soil or just use soil, then top with a thin compost layer.
-
For transplants, add extra perlite or vermiculite to pure compost to improve drainage and aeration.
-
To conserve expensive compost, amend just the planting holes with compost when planting in native soil beds.
-
Watch moisture carefully and water pure compost more frequently, especially during hot, dry spells.
-
Test soil fertility before planting and reduce any compost or fertilizer amendments as needed to avoid overfeeding plants.
-
Keep a close eye on seedlings and transplants for signs of nutrient stress like leaf burn. Flush soil with water if issues appear.
Compost Must Be Completely Finished Before Planting
No matter how you choose to use compost in your garden, there is one golden rule – it must be fully finished decomposing before planting.
Immature compost can damage or kill plants due to:
-
High temperatures that “cook” plant roots and leaves
-
Lack of oxygen with anaerobic bacteria still at work
-
Phytotoxic compounds present mid-decomposition
-
Ammonia content that chemically burns plants
Signs that compost is not ready for planting include:
-
Warm temperature and strong ammonia odor
-
Little dark brown crumbly material; still decomposing
-
Visible uncomposted materials like sticks or leaves
Only use compost that is fully broken down and resembles dark, crumbly soil. Then decide whether straight compost or a blended mix will give your plants their best start. With the right precautions, planting in compost can nourish an abundant garden.
Compost as a Garden Amendment
When using compost to fortify gardens, incorporate it evenly into your natural soil. It should be added in large amounts if your soil isn’t very good, especially if you want to grow fruits and vegetables that need rich soil. You might also consider building raised beds to make the most of your compost bounty.
Can you grow in only compost?
FAQ
Can I plant in 100% compost?
Can you use compost instead of potting soil?
Do plants grow well in compost?
Can I plant in finished compost?
Should you plant in pure compost?
So while it may be tempting, planting in pure compost is not a good idea. That’s not to say you shouldn’t plant in compost at all. Just an inch or two of good compost mixed with your existing topsoil is all your plants need. Gardening tips, videos, info and more delivered right to your inbox!
Can you put compost in a garden?
Mixing compost into your soil can be a bit of work, but there’s an even easier no-dig gardening solution. Use compost in planting beds as a side dressing or top dressing. Simply spread a thin layer of compost on top of the soil in empty beds in spring or autumn. Then allow the rain to wash the nutrients deep into the soil to your plants’ roots.
Should I use a mix of compost with garden soil?
Even with mature compost, it’s advisable to use a mix of compost with garden soil to provide a better structure for plant roots and ensure adequate drainage. When considering which plants are suitable for direct planting into compost, opt for those that benefit from rich, organic materials:
Can I plant a plant straight into compost?
Where possible, we always recommend that you DO NOT plant straight into compost. Unfortunately, pure compost doesn’t have all the nutrients that plants need to thrive. The fact that compost struggles to retain water without being mixed with soil proves this point further.
