Starting Seeds in Compost for Your Vegetable Garden

Gardeners often ask if starting seeds in compost works since it seems to be the least expensive option at the garden center. Let’s go through the benefits and risks on starting seeds in compost as opposed to bagged garden soil.

Starting Seeds in Compost is Easy

Every year, in my very lazy compost pile near the garden, I find healthy seedlings volunteering their way into existence. I didn’t plant them, I didn’t tend to them, and somehow, they seem to be the strongest little plants.

Eventually, I began thinking. Why have I not been starting seeds in compost all along?

If nature can do it perfectly, surely I can fumble my way through it. It must be easy enough.

Times Are Different

Our ancestors didn’t have fancy bagged soil to choose from. Starting seeds in compost used to be widely recommended over planting in native soil. Furthermore, the native soil usually didn’t (doesn’t) have much nutrients for the seedlings.

Homesteaders made compost from animal manures and kitchen scraps to plant in the following season. They also used weeds and garden refuse. They became excellent at making the best compost, but it was not the same each time because available materials changed constantly.

Now, we have endless options to choose from between our big box stores, farm stores, and online ordering. Our ancestors couldn’t have imagined our dilemma of wondering if starting seeds in compost would be possible.

hand-holding-compost-with-grass-background

Different Composts

Which type of compost will give you the best start for your seeds? Check out these options.

Mushroom compost can have high salt content so it is generally not recommended to start seeds in.

Peat-based compost can work if its fluffy enough to allow air for good drainage.

Peat-free composts can also work just fine. Many gardeners choose to use peat-free as its environmentally friendly. Instead, the manufacturer uses coconut coir.

Your Own Compost

If you’re going to use compost, go ahead and try your own homemade compost. You don’t even have to worry about the right ratios of greens and browns. Put some organic material together, wet it down, let it sit.

Undoubtedly, if you turn it every couple of days, you’ll have something worth using in 4-6 weeks.

Let your compost pile sit for a while without turning, and eventually, the bottom and inside will be compost material that you can use.

Does this sound like something an experienced gardener is expected to say? Probably not. Like I said up front, my lazy compost mix grows food for me every year.

How I Do It – Multi-purpose Compost

I often start seeds in 50% compost and 50% peat moss. I may use my own garden compost or any bagged compost from the store. This works well adding to garden beds too for building soil fertility.

To be truly transparent, this is the least expensive way I like to start seeds, but it’s not the only way. I often buy bagged soil as previously mentioned regarding planting tomatoes. I frequently change up my methods based on current budget, life circumstances, and availability.

The Danger of Starting Seeds in Compost

There is a pretty significant drawback to starting seeds in compost, damping off disease.

Damping off disease is a common term used to describe a group of soil-borne fungal diseases that affect the seeds and seedlings of plants. These diseases can be caused by various fungi. It typically occurs in young plants during germination and early growth stages.

Symptoms of damping off include the rotting of seeds before germination, as well as the decay of emerging seedlings at the soil line. Affected seedlings may appear water-soaked, wilted, and have a discolored and mushy stem. The disease can lead to stunted growth or death of the affected seedlings.

Preventive measures include using well-draining soil, providing proper ventilation, and especially avoiding overwatering. I like to spray my seed trays and the top of the planted compost with a diluted neem oil spray to help prevent damping off. Anti-fungal treatments are not likely to be effective.

Weed Seeds

While making your own compost is a great idea, you may end up with weed seeds in your garden. Even small amounts of added weed seed in your new beds can be a hassle. Be watchful for weeds and be prepared for a regular maintenance schedule.

For best results, make sure that the compost has properly reached the optimal temperature of 130°F in order to kill weed seeds.

Seed Germination Rate

Seeds will germinate with water, warmth, and some sort of medium. Germination rates are the same if you are starting seeds in compost, pure sand, quality soil, or a damp paper towel.

The seed has everything that it needs to get off to a good start. Because of this, the amount of nutrients doesn’t make much difference for germination.

However, use of compost should be done carefully to avoid that dreaded damping off disease.

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Maturity

Determining the maturity of compost is certainly important to ensure that it is fully stabilized and ready to use in your garden. Mature compost is rich in nutrients, has a pleasant earthy smell, and poses no risk of burning plant roots due to high levels of decomposition. Here are some signs that your compost is mature:

Color: Mature compost is typically dark and crumbly. It should have a rich, dark brown or black color, indicating that the organic material has broken down thoroughly.
Texture: The compost should have a crumbly texture, resembling soil. It should no longer resemble the original raw materials and should be free of recognizable pieces.
Odor: Well-matured compost has an earthy, pleasant smell. If your compost smells fresh and earthy, without any foul or ammonia-like odors, it is likely mature.
Temperature: Initially, compost piles generate heat as microorganisms break down organic matter. When the pile cools down and reaches ambient temperature, it’s a sign that the composting process is complete. Using a compost thermometer can help monitor temperature changes.
Time: Composting times can vary, but a well-managed compost pile can take a few weeks to several months to mature. It’s generally a good practice to let the compost sit for a few weeks after the active composting process before using it.
Absence of Uncomposted Materials: Mature compost should not contain large, recognizable pieces of organic material. If you still see chunks of undecomposed material, the compost may need more time.

Airy, not Soppy

The best seed compost should not be sopping wet. Instead, you need a fluffy, airy compost that will surround the seed when dampened, but still allows water to easily drain. Getting air to the roots of your healthy seedlings is just as important as water. Keep this in mind when you’re planting your vegetable seeds.

Beware of Herbicides

If you’re using horse manure or cow manure to compost for your garden, be careful that you aren’t adding herbicides to your garden. The same can be true of grass clippings. Persistent herbicides will take years to compost down.

Putting your baby plants in contaminated soil will at least ruin your garden season. Ask your manure supplier, or hay supplier, if the feed that is fed to the animal that you’re collecting manure from was sprayed with long-term herbicides.

What Kind of Seed Trays Do I Need When Starting Seeds in Compost?

You can use any kind of seed starting containers that you’d like. From homemade pots like Solo cups or used yogurt containers, to the real deal professional pots, use whatever you want.

I do recommend that the containers have holes in the bottoms. Make sure they fit in a tray that will hold water so that you can bottom water the cups.

Best Practice for Starting Seeds in Compost

Starting seeds in compost can be a beneficial practice, as compost provides a nutrient-rich and well-aerated environment for seed germination. Here are some best practices for starting seeds in compost:

1. Choose Quality Compost:

Firstly, use well-matured compost that has a finer texture, dark color, and a pleasant earthy smell for your seed starts. Avoid using compost that is still decomposing or has an ammonia-like odor.

2. Use Sterile Containers:

Start seeds in clean and sterile containers to prevent the introduction of pathogens. You can use seed trays, peat pots, or other containers designed for seed starting. (Pro tip: spray the pots with neem oil before filling with compost.)

3. Moisture Control:

Keep the compost mix consistently moist but not waterlogged. Seeds need moisture to germinate, but excess water can lead to damping off disease. Use a spray bottle for gentle watering, or bottom water.

4. Provide Adequate Light:

Next, place seed trays in a location with sufficient light. A sunny windowsill or using artificial grow lights can help seedlings receive the light they need for healthy growth.

5. Temperature Considerations:

Maintain an optimal temperature for seed germination. Different plant species have different temperature requirements, so be aware of the specific needs of the seeds you are starting. A heated seed mat beneath your trays is a good idea for warmth-loving plants.

6. Thin Seedlings:

Once the seedlings have emerged and developed a few sets of leaves, thin them to ensure proper spacing and encourage strong, healthy growth. Crowded seedlings can compete for resources.

7. Harden Off Before Transplanting:

Before transplanting seedlings outdoors, gradually expose them to outdoor conditions through a process called hardening off. This helps seedlings acclimate to changes in temperature, wind, and sunlight.

8. Transplant at the Right Time:

Transplant seedlings into the garden or larger containers at the appropriate time for each plant species. Consider factors like the last frost date and the specific needs of the plants.

9. Monitor and Adjust:

Keep a close eye on your seedlings. Adjust watering, light, and other conditions based on the specific requirements of the plants you are growing.

When Do I Transplant My Young Plants Outside?

Before transplanting your new plants, make sure that they at least have their second set of true leaves and you have hardened them off.

I like to grow them a little longer for more mature plants before transplanting into my own raised bed because they’re stronger.

Additionally, if you’re moving warm season loving vegetables to your garden, then make sure your last frost has passed.

Summarizing Starting Seeds in Compost

It’s not rocket science. The bottom line is that seeds want to grow, so don’t over think it. Grab some compost and some pots, and grow a little food of your own.