Can You Use Compost to Start Seeds?

Can You Use Compost to Start Seeds

Every time I go to a garden center, I am amazed at the variety of soils that exist for every stage of a plant’s development. What fascinates me is that I’ve seen almost every imaginable seed germinate freely in homemade compost. 

If starting seeds in compost lead to successful germination, is there any reason to buy special seed starting soil? After looking into it, I found a lot of interesting information. Read on to learn more.  

What Happens to Seeds Started in Compost?

Seeds started in compost can have access to nutrient-rich and moist soil that provides a boost for new seedlings. Compost can also lead to problems like dampening off and nitrogen deficiency. The result of seed germination in compost depends on how the compost is processed. 

The process of preparing compost for seeds is different than sowing manure in the field in the fall and letting it mature over the winter. Compost for seeds needs to be in its final humus stage. No anaerobic lumps or nitrogen-starved microbes can remain. 

When gardening with compost, you can let it break down and mix it with garden soil, but when starting seeds, you need to sift it to unearth the finest layer possible. Shift onto a tray until it is a finer texture like potting soil. Compost prepared like this will be a perfect medium for starting seeds.

If you use compost that has too much moisture or has a large amount of fertilizer, you may kill the seeds before they sprout. Correct amounts of water need to be applied at the right times to allow seedlings to adjust to the diversity of compost.

Pros and Cons of Starting Seeds in Compost

Compost can make a quality seed starting soil comparable to potting soil with peat moss and fertilizer as ingredients. However, seed packets recommend against using compost to start seeds. Below are some reasons for and against getting plants started in compost. 

ProsCons
Slow-release fertilizersNitrogen stealing bacteria 
Great Nutrient Profilepesticide and herbicide from ingredients
Quality soil structureInconsistent lumps and chunks
Good Moisture RetentionStagnant areas and pest nests
Diverse bacterial and fungal networkWeed seeds and pathogens

Pros

Slow-Release Fertilizers

Potting soil and peat moss tend to release their nutrients quickly and then break down. Organic compost has everything a plant needs but leaves it suspended until a plant chooses to access it. At compost maturity, seeds in compost have access to everything they need for root growth and leaf development.

Great Nutrient Profile

Seedlings in compost have the nutrient variety needed to develop from a small sprout to a massive plant. Homemade compost can provide the nutrients a plant needs for its entire lifecycle. 

Quality Soil Structure

One of the main reasons seeds don’t germinate is the soil structure thwarts their initial explosive growth. If the seed’s energy is insufficient to break the soil surface, the plant can not grow. Sifted homemade compost is fine enough for seeds to grow up through, as is traditional potting soil. 

Good Moisture Retention

Watering seedlings is tricky. Too much water can cause fungal disease, so seed-starting mixes are sterile. But seeds in compost have the benefit of having soil that drains quickly while still holding moisture long enough for seeds to sprout. 

Diverse Bacterial and Fungal Network

Plants, like all creatures, survive best in a community of symbiotic relationships. The bacteria and mycelium found in garden compost help convert all organic matter in the soil into readily digestible plant food for your new sprouts. 

Cons

Nitrogen Stealing Bacteria

If homemade compost has not completely matured, some of the nitrogen-eating bacteria in compost will still be active. Since plants need nitrogen for their growth and leaf development, an early nitrogen deficiency can stunt plant growth for life. 

Pesticides and Herbicides in Compost Ingredients

It is impossible to tell where everything that goes into our garden compost originates from and what it may have been treated with. If you have added waste with pre or post-emergent herbicide, then your seeds may not germinate. 

Inconsistent Lumps and Chunks

Compost that has not been properly sifted can harm plants and seedlings. A lack of oxygen in these clumps can cause root development to halt. Compost must be sifted or crushed to a crumble by gardeners before being used to start seeds. 

Stagnant Areas and Pest Nests

Garden compost can have areas full of methane and anaerobic conditions. When mixed, the release of all the build-up of gasses and the potential pests living in these pockets of decay can quickly kill a new seedling. 

Weed Seeds and Pathogens

Commercial compost gets heated well above 140 ℉, and UV lights kill pathogens, diseases, and weed seeds present in the compost materials. Homemade compost may not reach those temperatures and can still have weed seeds and diseases alive inside. New plants may be susceptible to these environmental conditions. 

Seedlings

How To Prepare Compost for Seed Starting Success?

The bottom line regarding using compost to start seeds is that it is all in the preparation and source of the compost. If you prepare the compost correctly and use quality materials in the correct ratio, you will be able to start seeds successfully. 

The steps to prepare compost for starting seeds are: 

  1. Make sure the compost has matured and contains only aerobic compost and worm castings. Anaerobic compost will harm seedlings and prevent germination. Oxygen is important for root growth.
  2. Take the compost and sift it through a screen to collect fine grains of compost on a tray or in a bucket. Larger chunks can be made into compost tea or tossed into worm compost. 
  3. Place the humus compost in a shallow seed tray or other seed starter container. Follow the seed packet instructions and sow the seeds at the correct depth. 
  4. Give the seeds watering mists twice daily, morning and evening, and adjust grow lights to increase humidity. Allow the soil to dry out and oxygen to replenish before watering again. 
  5. Once the seedlings have started growing, give them the lights and water they need until the plants are ready to transplant. If starting seeds in compost outside, choose the correct season to grow each type of plant. If growing in potting containers, move them with care to adjust to the appropriate lighting needs and weather conditions.