10 Plants That Like Wood Ash (Top Species)

When considering which types of fertilizers to use for plants, it’s always best to have natural or organic products on top of your list. These are less likely to harm the environment if they are released into waterways or eroding substrates. Wood ash, a natural byproduct of wood combustion, is considered an ecologically friendly fertilizer and compost material that effectively enriches soils.

The composition of wood ash is highly variable as the type of wood, temperature at which it combusts, and exposure to air influences its chemistry. Calcium carbonate is generally the most dominant component. Other constituents include trace elements such as potassium, phosphorus, magnesium, sodium, iron, silicon, copper, and zinc. These elements are essential for the growth of new plant tissues. These can also help induce flower and fruit production.

As wood ash contains a high amount of calcium, potentially in carbonate form, you can expect it to act as a liming agent for the neutralization of overly acidic soils. This means that plants with a preference for acidic soils are less likely to benefit from its application. Another major consideration is the source of wood used to produce the ash, as trees from industrial sites may harbor dangerous toxins. For the plants listed below, aim to use wood ash sourced from trees grown in unpolluted areas.

1) Lavender (Lavandula spp.)

Well-loved all across the globe for its colorful inflorescences, hardy stems, and fragrant foliage, lavender has a place in every garden. Demand for its essential oils, which have varied phytochemical concentrations depending on species and growth conditions, has spurred widespread commercial cultivation. As a result, natural types of fertilizer are an absolute must to minimize ecological impacts and production costs.

As lavender species prefer to grow in slightly alkaline soil, a liming agent must be used to raise the pH of acidic substrates. Though wood ash is not as potent as agricultural lime, it is more reactive and can be applied at higher concentrations to increase alkalinity. Apart from creating a better environment for lavender roots, it would also help protect the plant from pests and diseases.

Annually dusting wood ash onto the soil around the base of lavender shoots should work wonders. Additionally, a little bone meal should help lavender plants obtain the necessary elements for new growth. Ensure that your lavender plants receive ample sunlight and ventilation so that any supplementary fertilizers can work effectively. 

2) Basil (Ocimum basilicum)

A tender perennial, basil is an absolute must-have in any herb garden. This fragrant and incredibly tasty plant is now cultivated in all sorts of creative ways. Vertical gardens and fully hydroponic setups are just the tip of the iceberg when it comes to ensuring high-quality basil leaves can be marketed everywhere.

Basil prefers to grow in slightly acidic to neutral conditions (pH 6.5 – 7.5) in soil. In an aquaponic setup, it may benefit from a slightly higher pH. When dealing with overly acidic soils, wood ash comes in handy as it is a natural source of pH-raising compounds. When adding wood ash to a soil mixture, always stick to conservative amounts, making sure to measure the pH after every addition. You can use a trowel to work the ash up to 6 inches (15 cm) deep into the soil. Once the pH is at around 6.5, you may stop adding ash.

Though wood ash is not necessarily a plant food for basil, adding it to the soil has other benefits. It can help deter insects that love to graze on the soft, vegetative parts of the plant. Hungry cutworms and the larvae of other insects are effectively warded off by wood ash particles. The ash tends to strip their bodies of moisture and cause them to dry out. Again, when adding wood ash for this purpose, don’t forget to test the soil’s pH levels before and after application.

3) Tomato (Solanum lycopersicum)

Practically all types of tomatoes will greatly benefit from the application of wood ash in their surrounding substrates. The dominant and trace elements in most wood ash compositions help prevent tomatoes from becoming calcium-deficient as they grow. Moreover, these nutrients can significantly aid in increasing crop yield, improving the color of tomato fruits, and keeping the leaves strong and green. Interestingly, research into the effects of wood ash on S. lycopersicum growth has explored its effectiveness in conjunction with human urine.

Wood ash should come in handy if your soil pH is below 6. Tomatoes prefer slightly acidic soil, and they are less likely to take up nutrients in overly acidic substrates. Gradually add the ash to prevent drastic spikes in pH levels. Compared to agricultural limestone, wood ash tends to neutralize the soil at a quicker rate as it is water-soluble. Moreover, it is less likely to raise the pH to dangerous levels.

If you intend to use wood ash to protect your tomatoes from pests, aim to apply it once morning dew or excess moisture has evaporated. The ash particles are only effective at deterring pests when they are dry. The dry ash should be sprinkled around the base of the plant and should be kept away from the leaves or stems. The fine particles may damage the plant’s epidermal tissues or compromise photosynthesis rates.

4) Sweet cherry (Prunus avium)

The productivity of fruit trees is largely affected by nutrient and pH levels in the soil. For maximum yields, soil conditions need to be perfected and maintained throughout the tree’s peak growth periods. Cherry trees favor a slightly acidic to moderately alkaline pH in the soil, so wood ash comes in handy whenever pH levels drop to below 6. If you’re concerned about drops in pH over time, you can amend the soil until the measured pH level is close to neutral.

The potassium in wood ash should help sweet cherry trees produce a higher abundance of flowers and a desirable fruit quality. Keep in mind that fruit and flower production tend to use up a significant portion of the plant’s nutrient stores. Thus, the application of wood ash should either be timed with the tree’s peak growth period or be done even before the sapling or tree is planted.

To further improve the growth of cherry trees, make sure that they are exposed to full sunlight and receive good air circulation. The substrate that surrounds the root system should be fertile, well-draining, and fairly deep. This species is quite susceptible to root rot; the provision of wood ash will not help with fruit production if the roots are already in bad shape due to poor drainage.

5) Asparagus (Asparagus officinalis)

A vegetable that has staked its identity in dozens of international cuisines, the humble asparagus is known for its tasty, young shoots (“spears”). Whether you intend to cultivate asparagus as a harvest crop or as a mature, seed-producing perennial, you’ll want to explore the effects of wood ash on its growth. Asparagus is known for having a high tolerance for alkaline soils, so wood ash is unlikely to prevent nutrient uptake.   

For asparagus beds, wood ash can be worked through the upper layers of soil or it can be used as a topdressing alongside bonemeal or slow-release fertilizers. If you intend to raise the soil pH, it will need to be mixed into the substrate. As a thin layer above the topsoil, its nutrients should gradually leach downward and be accessible to the roots. Asparagus is known for being a big eater and will benefit from a rich substrate composition.

To enrich the soil in asparagus beds, you can also make use of compost that has been amended with wood ash. Compost that has been loaded with food-based waste tends to be highly acidic, so wood ash would help neutralize its pH and make it safe for use around asparagus shoots. Moreover, a moderate amount of ash should not adversely impact the beneficial communities of bacteria in the compost. 

6) Bigleaf hydrangea (Hydrangea macrophylla)

Known for its large, bright green leaves and bouquet-shaped inflorescences, the bigleaf hydrangea is a stunning ornamental plant with a magical quality – the colors of its flowers are affected by soil pH! A garden hydrangea and a small sack of wood ash are the perfect ingredients for a chemistry or botany project you’re unlikely to forget.

If the hydrangea flowers are blue, which indicates an acidic soil pH, amending the soil with wood ash should increase the pH and shift the availability of plant nutrients. A slightly alkaline pH causes the plant to produce pink to red instead of blue inflorescences as the flower pigments are changed. This phenomenon is caused by the hyperaccumulation of aluminum ions, which are more available in increasingly acidic conditions.

If your hydrangea blooms are already pink, the roots will not benefit from the provision of wood ash. You may still opt to use wood ash as a fertilizer to enrich the soil, but be wary of adding too much, as markedly high alkalinity may compromise the growth of the plant. If you would like a hydrangea bush to have maximum impact, you can try amending the soil around the base of alternating shoots. This way, the blooms will have an assortment of colors.

7) Garden phlox (Phlox paniculata)

Garden phlox is a lovely perennial with a penchant for creating enchanting mats of pastel-colored inflorescences. This plant often looks like it has come straight out of a fantastical tale, especially as its simple flowers can be abundant enough to produce an alluring fragrance that attracts a wealth of pollinators. The fine, sticky stems of phlox tend to reach a maximum height of about 3 feet (1 meter), so the blooms of a densely planted shrub can form a waist-high carpet in mid to late spring.

Hardy to zones 3 – 8, garden phlox is known for benefitting from the application of organic fertilizers, including compost, bio humus, peat moss, manure, and wood ash. The added nutrients should stimulate the production of larger and more densely-packed inflorescences. Moreover, it should help condition the soil and prevent pH levels from dropping.

Phlox dislikes sour or overly acidic substrates, so the regular application of a little wood ash should effectively maintain desirable pH levels. Phlox also greatly benefits from potassium, another element that is usually present in wood ash. Potassium helps increase its hardiness and resistance to diseases. It also helps prolong the longevity of blooms. 

8) Common sage (Salvia officinalis)

Now naturalized in many parts of the globe due to its ornamental and culinary appeal, common sage is a perennial herb with many attractive varieties. Its fleshy, fuzzy foliage is grey to light green in color, though some cultivars have variegation and purplish undertones. These are rich in many phytochemicals, which collectively compose a high-value essential oil.

Sage can tolerate strongly acidic to slightly alkaline soil conditions. The perfect pH range for optimal growth, however, is 6.0 – 7.0. Wood ash can help bring soil pH up to this near-neutral range and serve as a source of minerals and nutrients to hasten the production of leaves. It should also induce higher flowering and seed production rates.

While fertilization is great for plants that are grown for ornamental purposes, the resulting rapid growth rate may negatively affect the leaves’ flavor profile. Wood ash tends to be a milder fertilizer (“low-grade”) compared to synthetically-produced ones, so its controlled application should provide the plant with the necessary trace nutrients without drastically increasing its growth rate.

9) Arugula (Eruca vesicaria)

Arugula is an annual herb that is known for its slightly bitter taste and high nutritional value. It is distinguished by its deeply-lobed, bright green leaves and its small, white to purple-veined flowers. The leaves are a great addition to Mediterranean-style salads and pizzas. They are rich in magnesium, calcium, and manganese. These are elements that should ideally be present in the substrate or hydroponic solution to be present in the leaves.

For optimal growth, arugula roots need to be situated in a neutral to slightly alkaline growth medium. Wood ash can be used to help raise pH levels to a near-neutral value. This should help maximize nutrient availability and absorption. In aquaponic setups, wood ash is usually used in conjunction with mineral fertilizers and organominerals.

In exposed areas, such as outdoor vegetable patches, ash would help keep arugula leaves free of hungry pests. Its regular application as a topsoil conditioner should ensure that potassium is readily available for the plant’s use. Arugula shoots that are deficient in potassium are less likely to tolerate suboptimal temperatures and exposure to pathogens.

10) Roses (Rosa spp.)

Wood ash is a fantastic fertilizer for roses due to its trace mineral profile. Roses require a rich substrate mix to thrive. Ample concentrations of nitrogen, phosphorus, calcium, and potassium must be present in the soil to promote an abundant rate of flower production. These nutrients also aid in ensuring the roots and stem are robust enough to persist through seasonal fluctuations of temperature and moisture availability.

Most roses favor a soil pH that lies between 6.0 and 7.0. Overly acidic soils may increase the likelihood of root rot and can stunt growth. The amount of wood ash that must be added to neutralize the soil would depend on the initial pH levels. If the soil is already alkaline, avoid adding any wood ash as an overly basic pH will prevent the roses from taking up nutrients. If you’ve added too much wood ash, you may correct pH levels with the addition of peat moss or sulfur.

The best time to add wood ash to a rose bed is just before the peak growth period. The fresh dose of potassium may allow the blooms to last for much longer than they usually would. Once the growth period is over (toward the end of summer), it would be best to withhold the addition of ash. Adding this to the soil at such a late period may promote untimely growth that may unnecessarily expend the plant’s nutrient stores prior to winter.