There are times when plants require topdressing to grow better and thrive. If you’re growing plants in any of these conditions, you might need to topdress them sooner or later.
Topdressing replenishes soil nutrients. It should be used whenever plants are faced with a fixed, limited soil supply. It’s an alternative to repotting, fertilizing, and soil replacement. Knowing if you should topdress or do something else depends on the situation.
Large pots and containers – or simply large plants!
When a pot is too large and heavy, it’s impossible to repot.
- Topdressing is convenient and effective
- It eliminates the risk and effort related to heavy lifting.
Stone basins, marble pots, or pots that are simply huge can’t be easily tipped and emptied.
- Indoor plants that require lots of soil like a banana tree or indoor fruit trees are also heavy. Not because of the pot, but because of the volume of soil.
A layer of fresh, rich soil mix is added on top of existing soil.
- When the pot is already filled to the rim, it’s best to remove a bit of the top soil before adding new soil.
- This is what’s done through soil replacement.
Large and tall plants
In this case, topdressing large plants helps avoid accidents. Plants aren’t at risk of breaking, falling over, or bending leaves.
- It’s very useful to replace soil for large potted plants both indoors (such as Areca or large ZZ plants) and outdoors (like potted olive, potted orange and potted lemon).
Fragile and delicate plants
Other plants might not grow so big, but are extremely brittle and fragile like the jade tree.
- Indeed, succulents are very fragile plants. They often break a leaf or stem at the slightest touch.
Also for succulents, a precious characteristic is the delicate farina they acquire as they grow. This layer of whitish dust, similar to flour, is lost with a single touch of the finger. Repotting removes it almost entirely! It’s called epicuticular wax in botanical terms.
- Topdressing will preserve farina on glaucous succulents if performed carefully.
Lawns and grassy areas
Typically, a lawn grows, is mown, and trimmings are thrown out. This is the worst possible cycle for any living environment, since organic material is removed and never replaced. Here are a few reasons why topdressing is relevant and important for lawns.
- replenish nutrients
- de-compact soil
- increase water retention
- support lawn grass instead of weeds
- level out bumps and holes in the lawn
- reduces moss
Read our complete article about lawn topdressing to learn more.
Raised garden beds
In a raised garden, soil is stacked above ground level. Rain and watering tend to wash nutrients out. After minerals and elements have been flushed out through the bottom, any remaining soil is poor.
A raised garden bed will benefit from top-dressing every three to four years.
- An alternative to topdressing in raised gardens is to apply nutrient-rich plant mulch like ramial chipped wood.
Urban growing beds
There are two major reasons to topdress a growing bed in a city:
- Below the growing bed, soil is either far away or very compacted. Cement on all sides hinders breathing, as well as air and water circulation. It’s basically a large garden box walled out all around.
- Runoff that reaches the growing bed is laden with pollutants. Brick, cement, tar, pavement collect fine dust formed from worn out surfaces, roads and buildings. There is little organic matter and the soil becomes heavy.
In an urban garden or small masonry growing spot, topdressing will remove these heavy particles and replace them with light, fresh, clean soil mix and amendments.
It’s also helpful in tiny road-side courtyards and front gardens.
Trees in shallow or wet soil
Some trees can take difficult living conditions such as shallow soil or constantly wet soil. However, to thrive, they have the same problems a houseplant does: lack of nutrients. Indeed, after years of growing, the tree has nibbled away at the available soil and extracted most of its nutrients.
- In shallow soil with nearby bedrock, roots don’t have much soil to work with in the first place.
- Roots can’t grow well in soil that is constantly wet. They need air to breathe, so they’ll always remain in the shallowest portion of the ground. The top four to six inches (10 to 15 cm) tend to drain or dry up enough for roots not to rot. Even though the area may be broad and wide, such a thin slice of earth usually isn’t enough for a grown tree.
Some trees that can cope with these conditions nonetheless require rich soil. They rapidly exhaust whatever nutrients are initially contained in the swath of soil that’s available. Topdressing compensates this by replenishing these nutrients!
- Typical trees that will love being topdressed in these conditions are, for example, the elegant katsura tree and the weeping willow.
Decompacting forest soil
In forestry, heavy machinery or constant passage of trucks compacts soil.
- Spreading a layer of special topdressing atop these pathways and ruts will attract worms and insects. These will decompact the soil very effectively!
- The best topdressing mix in this case is RCW (ramial chipped wood), mentioned above.
This should be practiced on temporary, one-time pathways that are set up to harvest and collect the wood.
In every forest, there should be a set of dedicated, permanent passageways used for monitoring and access. These should be maintained as well as possible to ensure all traffic only stays on them!
Poisoned soil that’s killing plants
It’s easy to make mistakes with chemical products. Too much herbicide, pesticide or weedkiller might contaminate the soil.