Composting is one of the best things a gardener can do for their soil. Compost adds nutrients, improves soil structure, and increases moisture retention. Gardeners often mix compost into their existing soil before planting. However, some gardeners take it a step further and plant directly into pure compost.
Planting into pure, finished compost can provide benefits but also has some drawbacks to consider. With the right plants and preparations, planting into undiluted compost can result in thriving, productive gardens.
Can you plant directly in Compost?
Yes, you can plant directly into compost, but it is generally recommended to mix compost with other soil or to use it as an amendment rather than planting directly in pure compost. Compost is rich in nutrients and organic matter, but it may not provide the best structure and aeration for plant roots.
Planting in pure compost can sometimes lead to compaction over time. The pH balance and nutrient ratios may not be optimal for all plants. Taking these factors into account, gardeners can decide when pure compost provides the perfect growing medium.
Benefits of Planting in Straight Compost
Using finished compost as the sole growing medium offers some potential advantages:
Nutrient Rich
Compost contains a mixture of macronutrients that plants need – primarily nitrogen, phosphorus, and potassium. As organic matter breaks down, these nutrients are released in plant-available forms. This means fewer fertilizers need to be added when growing in compost.
Excellent Water Retention
The spongy texture of compost enables it to soak up and hold onto moisture. Compost can store up to 90% of its weight in water. This helps maintain consistent moisture for plant roots.
Promotes Strong Root Growth
The loose structure, moisture, and nutrients in compost all encourage prolific root system development. Compost contains humic acids that stimulate root growth. Healthy roots allow plants to better access nutrients and water.
Contains Beneficial Microbes
Compost is a haven for diverse soil microorganisms like bacteria and fungi. These microbes aid plants by fixing nutrients, building soil structure, and preventing disease. Compost’s biological activity boosts plant health.
Weed Reduction
Composting generates high heat that kills weed seeds and pathogens. Weed problems are less likely when planting into cured compost compared to garden soils.
Environmentally Friendly
Using compost is a sustainable growing practice. It recycles nutrients and organic matter that would otherwise be discarded. Compost also increases carbon storage in soils. Overall, composting reduces waste and improves soils.
Drawbacks of Pure Compost for Planting
Despite its advantages, pure compost does have some limitations for planting:
Prone to Compaction
Over time, compost can become compressed due to watering and plant growth. This squeezes out the air pockets that plant roots and soil organisms rely on. Mixing compost with sand or gravel improves aeration and drainage.
May Lack Proper pH
Compost pH usually falls in the slightly acidic range, between 5.5-7. While some plants thrive in acidity, others need a more neutral pH around 7. Lime can be added to elevate pH if needed.
Nutrient Imbalances
The nutrients in compost are not always perfectly balanced. It tends to be higher in nitrogen and potassium than phosphorus. A complete fertilizer might be needed if plants show deficiencies.
Poor Structural Support
Compost is light and fluffy. Some plants with large fruiting bodies or extensive root systems need firmer support than compost alone provides. Staking or soil mixes can help give added strength.
Dries Out Faster
Compost dries out more rapidly than mineral soils. Vigilant watering is required, especially with raised beds of pure compost. Using compost to amend garden soil improves moisture retention.
By understanding compost’s potential limitations, gardeners can find solutions and work around them. With proper management, the benefits of planting in compost outweigh the disadvantages for many gardeners.
Best Uses for Pure Compost Planting
While compost as a sole growing medium is not ideal for all plants, some are well suited to being planted directly into cured compost:
Leafy Greens and Herbs
Lettuces, spinach, kale, chard, basil, cilantro, and other leafy greens thrive when planted in pure compost. Their shallow root systems appreciate compost’s loose texture and nutrient concentration near the surface.
Root Crops
Root vegetables like carrots, radishes, beets, turnips, and potatoes perform extremely well in compost. Their edible roots stretch freely in the loose, crumbly compost.
Brassicas
Broccoli, cabbage, cauliflower, Brussels sprouts, and other brassicas can all handle the lighter support and acidic nature of compost. The steady nutrition promotes excellent head formation.
Onions and Garlic
Bulbing alliums grow robustly in compost. The loose structure allows their round bulbs to swell uninhibited. Compost’s moisture retention prevents water stress.
Tomatoes
While staking is recommended, even tomatoes can fruit well when planted into pure compost. The nutrients and biological activity in compost give tomatoes the vigor they need.
Peppers
Like their relative the tomato, peppers thrive when planted directly into cured compost beds. Just be sure to provide adequate calcium and phosphorus.
Strawberries
Strawberries are shallow-rooted and enjoy acidic soils, making compost perfect for them. The nutrients result in abundant flowers and large, juicy berries.
Cucumbers and Melons
Vining crops like cucumbers, melons, and squash appreciate compost’s moisture retention and nutrient content. Simply guide their spreading vines and provide trellising or cages for support.
Flowers and Herbs
Many flowering annuals and perennials do well planted in pure compost, especially when they are not relying on deep roots. Rosemary, lavender, zinnias, and cosmos are great examples.
The ideal plants for planting directly into compost have roots that spread laterally near the surface rather than digging deep. Sturdy plants that need firmer anchoring are better suited to amended garden soil.
Preparing to Plant in Pure Compost
Proper preparation is key to success when planting directly in undiluted compost:
Use Only Finished Compost
Make sure compost is fully cured, with no unfinished chunks or recognizable bits of organic matter. Unfinished compost can stunt or kill tender seedlings. Curing stabilizes nutrients and neutralizes potentially harmful acids.
Check Compost Nutrients
Test compost’s pH and key macronutrients like nitrogen, phosphorus, and potassium. This allows you to adjust pH or add supplemental fertilizer to optimize conditions if needed.
Loosen and Smooth It Out
About a week before planting, rake compost to a depth of 8-12 inches, removing clumps and lightly firming. This evens out the texture and removes air pockets that can stunt root growth.
Moisten Thoroughly Before Planting
Fully hydrate compost a day or two prior to seeding or transplanting. Compost should feel like a wrung-out sponge. This ensures moisture and nutrients are evenly distributed.
Following these simple tips before planting helps avoid problems and gets plants off to a vigorous start in straight compost.
Planting Seeds vs. Transplants in Compost
Both seeds and transplants can be successfully planted into pure compost. However, seeds have some special considerations:
Direct Sow Larger Seeds
When sowing seeds directly, choose larger seeds and sow a little deeper than usual – 1/2 to 1 inch deep. This puts seeds in contact with stable compost and moisture to aid germination.
Cover Small Seeds Lightly
Very small seeds and seedlings like lettuce, carrots, and onions should be planted quite shallow in compost – no more than 1/4 inch deep. A light sifting of vermiculite over seeds helps retain moisture.
Use Seed Trays for Small Seeds
For the best results with small seeds, start them in seed trays filled with a compost-based potting mix. After sprouting, seedlings can be transplanted into pure compost.
Water Frequently After Planting
Check compost moisture daily and water as needed to keep the surface damp, especially in the few weeks after planting seeds. Use a gentle spray to avoid washing seeds away.
With extra care taken at sowing time, seeds can flourish when planted directly into compost beds. Transplanting sturdy young plants avoids tricky seed starting issues.
Maintaining Plants Growing in Compost
While compost contains ample nutrition, plants growing in pure compost still need proper care for sustained health:
Water Thoroughly
Check compost beds frequently, watering whenever the top few inches become dry. Compost dries out faster than soil, so sufficient water is essential. Target water at the roots, avoiding wet foliage which can encourage diseases.
Apply Supplemental Fertilizer
About 4 weeks after planting, begin applying a balanced liquid fertilizer every 2-3 weeks according to label directions. This replenishes nutrients as compost components break down.
Use Support Structures
Install stakes, trellises and cages to physically support larger plants or vines. Compost alone cannot hold up plants with heavy fruit, spreading vines, or top-heavy flowers.
Watch for Compaction
If puddles begin forming on the compost surface, gently fluff up compacted areas with a fork. A mulch layer also prevents compaction while conserving moisture.
Test and Adjust pH
Monitor compost pH using test strips and adjust mineral levels with lime (to raise) or sulfur (to lower) if needed. Shoot for a pH appropriate for the plants you are growing.
Topdress with Compost
Add 1-2 inches of fresh compost around plants once or twice during the growing season. This provides an added nutrient boost and helps reduce compaction.
With attentive care, plants growing in straight compost will thrive all season long. Avoiding problems is easier than correcting them later on.
Best Practices for Planting in Compost
Follow these tips and best practices when planting directly into pure, cured compost:
- Analyze compost pH and nutrient content before planting.
- Choose vegetable crops suited to compost’s loose, acidic nature like onions, greens, and root crops.
- Prepare beds by loosening compost to 8-12 inch depth and watering thoroughly before planting.
- Cover small seeds very shallowly or start them in trays; sow larger seeds 1⁄2 to 1 inch deep.
- Transplant seedlings or starters when they are 3-6 weeks old and well established.
- Water frequently to prevent drying out, aiming water at soil level rather than plant leaves.
- Apply balanced liquid fertilizer every 2-3 weeks to replenish nutrients.
- Install supports for vining, large, or top-heavy plants.
- Monitor for compaction and fluff up or topdress additional compost as needed.
- Adjust pH as required to keep in optimal range for chosen crops.
- Replenish beds with 1-2 inches of fresh compost at least once per growing season.
Following sustainable practices and paying close attention to plants’ needs makes growing directly in compost a very feasible gardening method.
Factors for Successful Pure Compost Planting
Several key factors contribute to productive results when planting into undiluted cured compost:
Compost Maturity – Fully finished, stable compost is essential. Unfinished compost can be too strong and compromise seedlings. Only use cured, dark, crumbly, earthy-smelling compost.
Aeration – Blending compost with a little sand or perlite provides air pockets plants need. Prevent compaction through fluffing and topdressing new compost.
Moisture Management – Compost dries out readily. Watch soil moisture closely and irrigate as needed. Use mulch to conserve moisture while allowing air circulation.
Macronutrients – Test levels of nitrogen, phosphorus, and potassium. Supplement based on plant needs and as compost nutrients deplete.
Support Structures – Stakes, cages, and trellises support plants that cannot stand upright in loose compost alone.
Soil Biology – Compost’s microbial community builds soil structure. Support it through proper moisture, limited tilling, and avoiding chemical pesticides.
pH Balance – Most plants need slightly acidic to neutral pH around 6.5. Lime raises pH while sulfur lowers it. Test and adjust as required.
Crop Selection – Choose crops suited to compost’s loose texture, moisture demands, and nutrient profile for best results.
With careful preparation, planting, maintenance, and crop selection, planting directly into pure compost can create bountiful harvests.
Mixing Compost with Soil for Planting
While some plants thrive in full compost, most benefit from mixing compost with soil or potting mixes. Combining compost with other elements creates a balanced planting medium.
Here are some ideal uses for blended compost:
In-Ground Beds – For in-ground gardens, mix 1-3 inches of compost into the top 6-12 inches of native soil.
Raised Beds – In raised beds, blend compost with potting soil or coconut coir at a ratio of 50/50 or 60/40.
Potting Mixes – For containers, combine compost with potting soil, peat, perlite and/or vermiculite at a 40/30/20/10 ratio.
Seed Starting Mix – For seed trays, use a mix of 1 part compost, 1 part vermiculite, and 1 part peat or coir.
Backfill Soil – When planting trees, shrubs, and perennials, blend compost with the backfill soil at a 1:3 ratio.
Sod Beds – Spread 1-2 inches of compost over soil and till in before laying new sod.
Used as an amendment, compost improves any soil or potting mix. The ideal blending ratio depends on the planting situation. Experiment to see what works best for your garden!
Conclusion
While planting directly into pure compost is not ideal for all gardening situations, the practice can provide benefits under the right conditions. For the appropriate plants, maintaining proper moisture, nutrients, and pH in compost enables thriving growth. Used alone or blended with other soils, compost is a key ingredient for sustainable, productive gardens and container plantings.