Can You Start Seeds in Compost? The Pros and Cons

I start all of my vegetable seeds in homemade compost, as I wrote about last month. (“Can you start vegetable seeds in compost?”) The results are satisfactory. Still I wondered how my seeds would germinate and grow in other composts. Would different composts yield clearly different results?.

Two other types of compost were compared in my experiment: compost from the Miramar Landfill in San Diego and compost from Mountain Meadow Mushrooms Farm in Escondido, which can be used to grow mushrooms for free afterward.

I want to make it clear right away that neither of these other composts says it is good for planting vegetables. Furthermore, Miramar specifically states, “Planting directly into compost alone is not recommended. ” Nevertheless, I was curious to see what would happen if I did.

The vegetable seeds I planted did well in my own compost, pretty well in mushroom compost, and not so well in Miramar compost. There were clear differences.

I planted two sets of seeds on March 23, 2021, in module trays that were full of each kind of compost. I tried to select vegetable seeds of different types of plants. The seeds were Toma Verde tomatillo, Top Bunch 2. 0 collards, Crispino iceberg lettuce, Summer Dance cucumber, Bright Lights chard, Caiman tomato, and Katana tomato. Immediately after sowing.

At sowing time I noted how each compost smelled, felt, and looked. I also kept in mind how each had been made.

Mine appeared to have the most diverse ingredients. In it I identified bits of leaves, twigs, soil, wood chips, and plenty of aggregates. It smelled neutral, a lot like dirt. My homemade compost.

This is true even though my compost comes from my mobile chicken pen, where I regularly put food and garden waste, wood chips from tree trimmings, horse manure, and urine. The chickens scratch through everything and add their own manure. They do also incorporate some of the dirt from the ground below. It all breaks down slowly and without ever getting hot.

On the other hand, Miramar compost contains no manure and goes through a hot composting process. For seventy days, yard waste and food scraps are ground up, put in windrows, turned, and watered at the Miramar Greenery. This is what their website says: Microorganisms break down the carbon and nitrogen-rich mixture during this time, keeping the windrow at 140 to 165 F. ” Miramar compost.

Miramar compost was dark compared to mine, almost black. I could see some small pieces of wood, but there were also a lot of small pieces that were squished together in the module tray’s cells.

The mushroom compost had the most odor. It didn’t smell exactly like manure, but I couldn’t think of a better word to use to describe it. Plus, it smelled better than real manure. The color was a pleasing dark brown. I could see many bits of straw, as well as some aggregates. It was the airiest, the fluffiest of the three composts. Mountain Meadow Mushrooms “spent” compost.

I recently took notes during a talk that Mountain Meadows Mushroom farm’s owner, Roberto Ramirez, gave. He said that the spent mushroom compost is made from horse stall manure and straw bedding, as well as gypsum, almond shells, cottonseed hulls, and alfalfa screenings. The materials are composted for about 20 days.

The compost is “spent” when it has been used to grow mushrooms. Some nutrients are lost during this process, but the compost is then made available to farmers and gardeners. I loaded my truck with some back in March.

What do you predict? How will the vegetable seeds come to life within each of these composts?

Here is what I saw: Some germination of collards in all composts after one week, March 30. Continued germination in mine and the mushroom composts seen on April 2.

On April 2, I made this note: “Miramar compost becomes hydrophobic, forming a black crust on the surface. Mine lets in water moderately fast. Mushroom lets in water immediately, fastest. ” April 5. April 10. Left to right: Mine, Mushroom, Miramar. April 16: Mine, Mushroom, Miramar. April 21: Mine, Mushroom, Miramar. April 25: Mine, Mushroom, Miramar.

At this point, the seedlings in my compost were at transplanting size so I considered the experiment done. Here’s another view of them on the last day: Mine, Mushroom, and Miramar, from left to right. (“C” is for Caiman tomato and “K” is for Katana tomato. ).

From germination through growth up to transplant size, seeds sown in my homemade compost performed best. A higher proportion germinated, and growth was fastest and appeared healthiest.

The mushroom compost performed far better than Miramar but not as well as mine. You could use this mushroom compost for starting vegetable seeds, but it doesn’t appear optimal.

The Miramar compost was not a friendly medium in which to germinate vegetable seeds. Only seven out of twelve cells had any germination — and I’d sown multiple seeds in each cell. The total germination rate was less than 50%.

Here are close-up pictures of cucumbers and their roots in each compost when the test was over: Mushroom. Miramar.

It’s possible that the different composts did different things for this job, but I’m going to make four points for you to think about.

Would the mushroom compost have done as well as mine, or even better, if it hadn’t been used to grow a mushroom crop and lost some of its nutrients?

Because the Miramar compost was dense and didn’t have any aggregates (clumps), did the crust that it made on top stop seedlings from sprouting?

The last question is whether the Miramar compost had any pesticides or herbicides that were still there and hurt the growth of these baby vegetables.

In the end, I think I need to do a second experiment to see how my compost stacks up against commercial composts made just for starting vegetables.

Starting seeds is an exciting time for any gardener. Soon, those tiny seeds will transform into an abundance of fruits, vegetables, and flowers. Many gardeners wonder if they can simply start their seeds directly in compost to get them off to a nourishing start. However, using compost for seed starting has both advantages and disadvantages to consider.

Why Use Compost for Seeds?

Compost has a number of beneficial properties that seem like they would aid seed starting:

  • Nutrients – Compost contains nitrogen, phosphorus, and other nutrients seeds need to germinate and grow. This saves the need to fertilize later.

  • Organic Matter – The organic matter in compost helps retain moisture while still allowing drainage and air pockets for healthy root growth.

  • Microbes – Compost contains beneficial microorganisms that may protect against soil-borne diseases.

  • Cost – Compost can be made for free from yard and household waste versus purchasing commercial seed starting mix.

With these benefits it seems compost would be ideal for starting seeds directly in it. However, there are some potential drawbacks to using compost that need to be considered as well.

Concerns With Using Compost for Seed Starting

While compost offers benefits. there are good reasons many experts recommend against starting seeds directly in compost

Disease Risk

  • Compost may harbor soil-borne pathogens like damping off fungi if not properly heated. These can attack tender seedlings.

  • Added nutrients in compost can feed diseases already present and cause them to multiply

Weed Seeds and Pesticides

  • Compost made from yard waste or manures may contain weed seeds that then germinate among the desired plants.

  • Persistent synthetic pesticide residues could potentially damage or kill germinating seeds and seedlings.

Improper C:N Ratio

  • Immature compost with a high carbon to nitrogen ratio can deprive seeds and seedlings of needed nitrogen.

  • High microbial activity in immature compost can lead to nitrogen draw down.

Poor Drainage

  • Dense compost with small particles can become compacted, leading to poor drainage and lack of oxygen to seeds’ roots.

Variable Nutrients

  • Nutrient levels in compost vary batch-to-batch making consistent results difficult. Seedlings may grow poorly or suffer nutrient disorders.

  • Excess nutrients, salts, or oils from composts like vermicompost can damage tender roots and leaves.

Due to these risks, many gardeners opt to avoid using home compost for starting seeds. However, with proper precautions, seeds can be started in compost successfully.

How to Start Seeds in Compost

If wanting to use compost for seed starting, following certain guidelines can help increase the chances of success:

  • Use well-aged, fully finished compost that has heated to at least 140°F for pathogen control.

  • Test compost maturity through a seed germination test. Make sure seeds sprout well.

  • Amend dense compost with perlite or vermiculite to improve drainage and aeration.

  • Mix compost with sterile seed starting mix at no more than a 1:3 ratio of compost to seed mix.

  • Sow seeds in sterile media first for 1-2 weeks before transplanting into compost mix.

  • Test compost for herbicide residues by germinating test seeds in just compost and looking for abnormalities.

  • Use compost made only from trusted, pesticide-free ingredients like on-site materials.

  • Rinse compost to remove potential weed seeds and drain well before using.

  • Monitor seedlings closely and discard any that appear abnormal or diseased.

When taking these extra steps, the potential risks can be reduced and compost can be used successfully for seed starting. However, it still poses more of a gamble than commercial sterile seed starting mixes.

Best Uses of Compost in Seed Starting

Rather than sowing seeds directly in compost, lower risk options include:

  • Mixing compost with sterile media at a 1:3 or 1:4 ratio for transplanting seedlings after sprouting.

  • Using finished compost to make DIY seed starting pellets, cubes, or pots for transplantation later.

  • Top-dressing seedlings with a thin sprinkling of fine compost once established for nutrients.

  • Watering seedlings occasionally with diluted compost tea for beneficial microbes.

  • Amending outdoor garden beds with compost when transplanting seedlings for added nutrition and improved soil properties.

In this way, seedlings can benefit from compost without being directly exposed to potential hazards in their delicate, early growth stages.

Best Practices for Starting Seeds

To get seeds and seedlings off to the healthiest start possible:

  • Purchase a commercial sterile seed starting mix for sowing seeds. Look for mixes containing peat or coco coir.

  • Sterilize reused seed starting containers with a 10% bleach solution or baking at 180°F for 30 minutes.

  • Allow seed starting mix to dry out slightly between waterings to prevent fungal disease.

  • Provide bright, gentle light right above seedlings with grow lights or south-facing windows.

  • Keep seedlings at 65-75°F until germination, then lower temperatures to 60-65°F.

  • Transplant seedlings to larger containers or the garden before becoming root bound.

  • Harden off seedlings gradually over 7-10 days before transplanting outdoors.

Following these simple practices, a bounty of thriving, productive plants can be grown from seed sustainably and successfully season after season. With just a bit of care and patience, the miracle of sprouting seeds never gets old!

Welcome . . .

Im Greg. You can grow food at home in Southern California. I want to help you grow vegetables, fruits, and especially avocados. I write a new “Yard Post” every Friday.

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Can you grow in only compost?

Can I make my own seed starting mix with compost?

Making your own diy seed starting mix with compost is really simple and cost effective! You are in control. Use your own compost or source it from someone trusted locally. Mix in all natural ingredients that don’t look like little pieces of styrofoam floating around in your soil (seriously, is that what’s actually in the store-bought stuff??).

Can you plant seedlings in compost?

Seedlings are young plants that have just germinated from seeds. Once they sprout, they must be transplanted into garden soil to continue growing. But can you plant your, say, veggie seeds in compost instead? The answer is yes! You can plant seedlings in compost. It’s a great way to give them a boost of nutrients.

Can seeds grow in a compost pile?

Seeds are organic material and will break down over time in a compost pile. However, if your compost pile doesn’t reach a high enough temperature to kill the seeds (at least 140°F or 60°C), they may remain viable and potentially germinate when you use the compost in your garden, leading to unwanted plants.

Can I compost seeds?

As an Amazon Associate I earn from qualifying purchases. Yes, you can compost seeds, but there are some considerations to keep in mind. Seeds are organic material and will break down over time in a compost pile.

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