How to Condition & Fertilize Straw Bales

Conditioning & fertilizing

One of the best aspects of straw bale gardening is the ready-made warmth the decomposing bales create. You’ll need to plan 10-14 days to allow the fertilizing and conditioning process to fire up. Nature will start rotting the bales for you, but to speed up the process you can add some ingredients to the mix.

How to add water and nutrients to fertilize straw bales

There are many methods for setting up your bales but they are all based around the same principles: get the bales wet and then feed them (this is because of the lack of nitrogen, as mentioned in chapter 1).

Below are two of the most popular methods, but you certainly don’t need to follow them to the letter. The bales won’t mind if you feed them on day 5 rather than day 4!

Use a good fertilizerFertilizer is crucial for keeping your plants healthy. Photo by Laura Hamilton

Finally, don’t panic if this part of the process seems labor-intensive and not too exciting (depending on whether you like hot, damp straw or not). Once your bales are up and running, especially if you incorporate a watering system (covered in chapter 2), you should be able to enjoy a summer of picking delicious fruit and vegetables with minimal effort.

Method One: Water and wait

If you prefer to follow a simple method, this is one of the easiest routes to take. It follows the principle of getting the bales good and wet before adding nitrogen via a simple organic fertilizer.

install drip feed irrigationRegular watering encourages plant growth in your straw bale garden. Here, a soaker hose is used to keep the bales damp. Photo by knitsteel

Day 1: Water the bales thoroughly.

Days 2-3: Water daily to ensure the bales stay damp. Push your hand down into the bales to check they’re damp inside – you should start to feel warmth, too, as they start to decompose.

Days 4-10: Feed the bales using a high-nitrogen organic liquid fertilizer – any standard vegetable and flower mix will be fine. Simply add it to your watering can as directed on the pack and pour onto the bales.

Days 11-13: Stop feeding, but keep the bales damp.

Day 14: Stick your hand inside a bale. It should feel warm but definitely cooler than your hand, which means the initial decomposition process has slowed down. You’re ready to plant!


If sticking your hand into the straw bale feels too icky, invest in a compost or standard meat thermometer with a long metal spike. You can watch the temperature rise daily, peaking around day 6 or 7 when the bales can be as hot as 150°F (65.5°C) inside. Once the temperature has returned to a level slightly above air temperature (known as ambient temperature), the bales are ready for planting.

Use a compost thermometerA standard compost thermometer works great for straw bales, too. Photo by fishermansdaughter

Method Two: Feed me baby

This method contains a higher level of fertilizer, and incorporates adding this food on alternate days from day one in order to get the decomposition going quickly. More suited to cooler climates where the straw bales will take longer to start breaking down.

Days 1, 3 and 5: Sprinkle 3 cups of organic, nitrogen-rich fertilizer on each bale and water them well, ensuring the fertilizer disappears inside the bale

Days 2, 4 and 6: Water the bales without feeding, keeping them damp

Days 7-9: Back to feeding: add 1.5 cups of organic fertilizer and water it in.

Day 10: Switch to a phosphorus and potassium fertilizer and water.

Days 11-14: Keep watering and checking the heat inside the bale – as before, if it feels cooler than your body temperature, you’re ready to plant.

Early stages: all’s going well if…

  1. The bales feel hot and damp inside when you stick your finger in.
  2. Tiny clumps of black compost start to appear inside the bale.
  3. Mushrooms emerge – don’t worry, they’re harmless to your plants. Mushrooms love fertilized strawPhoto by fishermansdaughter

How much water should I use?

One or two gallons should soak a bale but, as a rule, just stop when water starts coming out of the bottom of the bale. Water fairly slowly to allow the water to soak in, particularly in the early stages when the straw only starting to break down.

TomatoPhoto by knitsteel

Around day 5, when the bales should be fairly hot inside, switch to slightly warmer water if possible. If the nearest hot water faucet is too far away, this could come from a water barrel, or try leaving water in a watering can overnight. Of course, if there’s still a frost in the air this won’t work.

Joel Karsten’s Books on Straw Bale Gardening

Joel Karsten perfected the methods of straw bale gardening during more than 20 years and has written many excellent books about the subject. His books contain all the ins and outs on how to setup, condition and care for straw bales helping you to grow almost any plant in them.

For any serious gardener that want to take straw bale gardening to the next level his knowledge is a must have.

Which fertilizers to use for conditioning straw bales?

If in doubt, go for a multi-purpose organic fertilizer with a high nitrogen content, ideally a liquid feed. Granule fertilizers are generally more economical, but try to get the granules to dissolve as much as possible. Remember to water slowly to avoid as much seepage into the ground as possible – you want your fertilizer to be soaked up by the bales.

Organic fertilizerLiquid fertilizers are the easiest to apply, but granule or pellets work too if you dissolve them in water. Photo by Oliver

Which nutrients do you need?

All plants, whether they’re grown in soil or straw, need a few basic nutrients to grow healthily. Nitrogen, phosphorus, potassium, and calcium are four of the most important.

Organic garden fertilizerPhoto by Doug Beckers

Best organic fertilizers for straw bale gardening

For organic gardeners, here are a few of the many options available:

  1. Seaweed mix: Seaweed mixes are great for improving yields for fruiting plants like tomatoes, potatoes, peppers, and cucumbers, as seaweed contains many enzymes and minerals that aren’t found in other fertilizers.
  2. Fish oil: Fish oil is high in nitrogen and amino acids and also provides potassium and phosphorus; in other words, it has most of the nutrients that you find in chemical fertilizer. Fish oil becomes available to plants in just 1-2 days, so it’s perfect for providing an early growth boost before planting.
  3. Compost “tea”: Compost tea provides an effective boost for garden plants, can suppress fungal diseases and provide beneficial microbes, and tends to make nutrients available to plants more quickly than chemical fertilizer.
  4. Bone or fish meal: Bone meal provides phosphorus, nitrogen, and calcium, while fish meal offers nitrogen, phosphorus, and potassium.
  5. Composted or sprinkled wood ash: Wood ash provides a lime and potassium boost and can be sprinkled around your plants for pest control. Use it sparingly sprinkled around your plants—when it gets wet it produces salts that can damage crops in large quantities. To avoid this, add it to your compost first to give the salts a chance to drain away.

Picking the right plants

Once your bales are ripe with necessary nutrients and moist with water, it’s time to delve in to the fun part: picking the plants for your garden. In chapter 4, you’ll learn about the vegetables, fruits, and flowers that thrive in straw bale gardens.

Share your thoughts

  1. Brenda Shumpert

    My bales never got warm Above 70 degrees Fahrenheit but I have mushrooms galore! May have used the wrong fertilizer because I have grass growing all over the bales. The bales have decomposed and appear to be ready for my plants. But the temperature never rose… it ready? (Yes I did get organic fertilizers and followed the watering and fertilizer schedule listed in the how to guide). Waiting for the reply

    • Lisa Row

      Hi Brenda!

      If you are in a cooler area it may take longer for the bales to decompose. But if they seem ready they probably are. Grass can be pulled out fairly easily before planting.

      Good luck!

  2. Loretta Andry

    On 13th day how much potassium and phosphorus do I add per bale?

    • Erica

      1/2 cup per bale

  3. Marianne whitehouse

    I have calcium nitrate to use as a conditioner. Is that OK and how much do I use?

  4. Dave

    Can I use last year’s straw bales again this year

    • Patrick

      Yes you can, as long as the bales are still stable. Mostly they won’t last for much longer than 2 seasons.

  5. Michelle Fitzhugh

    What does it mean if I don’t have any mushrooms growing but I have followed the directions? I live in South Alabama. We are having uncharacteristically cool weather right now. Not sure if this is a factor. Thanks for your reply.

  6. Kelly Kozicky

    Hi, Can I use blood meal as a nitrogen source?

  7. Doug

    What is the best fertilizer to use after you have planted and once a month or when ?

    • Greg

      I’ve had good results using a 10-10-10 weekly or bi-weekly depending on a particular plantings needs. I also top dress with dolomite lime on day 5 of bale prep. Then once a month during the growing season. Using 1 cup each time. I have found this particularly important when growing tomatoes and peppers.

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