Topdressing, what is it?

Topdressing means to spread or disperse a fresh layer of new soil mix directly atop the ground to give plants the organic matter needed to grow best.

Top dressing is for lawns, plants in large containers or pots, along edges and in raised garden beds.

You can also use compost, which has fertilizing properties and will cover the needs of your plants for at least a year.

What is topdressing?

Topdressing is a technique or practice where a layer of fresh, extra soil is added on top of existing soil. The goal is to rejuvenate soil and replenish its nutrients.

“Topdressing” is also the noun that designates the material or amendment itself (usually soil mix or sand).

  • You topdress a plant with topdressing.

Topdressing, a technique with many advantages

Topdressing a plant or lawn is a good way to care for it. It helps reduce the need for frequent fertilizing.

  • This operation helps soil become richer in terms of organic matter.
  • It also helps soil stay airy and light, fighting the natural tendency of soil to grow heavier over the years.
  • Topdressing enhances soil structure.
  • Soil that is well structured has superior water retention properties and is a more fertile environment for plants.
  • When you add soil mix or compost, the ground grows more porous. This maximizes local gaseous exchanges that promote proper root growth.

Furthermore, there are positive side effects:

  • no need to fertilize during the first year
  • water needs are reduced
  • containers and pots seem refreshed and don’t need ornamental mulch for a while.

When is topdressing applicable?

Topdressing replenishes soil nutrients, so 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

Topdressing is called for in this heavy marble pot.When a pot is too large and heavy, it’s impossible to repot. Topdressing is convenient and effective, and eliminates the risk and effort related to heavy lifting. 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.

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).

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.

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.

How to topdress

Topdressing a lawn

The goals is to spread a very thin layer of soil mix across the entire surface of the lawn.

  • This layer should only be ¼th to ½ inch thick, or 0.5 to 1 cm.

Although it’s possible to simply throw the soil around with a wide movement of the arm (as if you were broadcast sowing seeds), there are other techniques that produce better results with specific equipment.

Topdress a houseplant

Hands working to topdress a houseplantSome indoor plants require rather large pots, such as indoor banana or citrus trees. Since repotting them is almost impossible due to size, the next best option is to topdress them.

  • Bring the pot over an easy-to-clean surface like tiles or spread a tarp under it.
  • Gently dig out soil out from the top with your hands. You can break the soil up a bit with a cultivator, but it’s best not to use tools because roots may be damaged.
  • Remove dirt until the root ball is exposed (topmost roots showing).
  • Fill in the space you made free with topdressing mix.
  • Press down, and keep filling until you reach the crown of the plant, where the soil level used to be.
  • Water and if more space is available, add a few final handfuls of topdressing mix.

Usually a large plant will benefit from being topdressed every two years. You can also support growth with natural fertilizer such as fermented tea.

How to topdress a large garden box or a raised bed

As long as there’s still space under the rim of the growing bed, you can topdress very easily simply by adding a thin layer of topdressing at the top.

  • Break the crust on the surface, if any, with a cultivator.
  • Compute the amount of topdressing you need. Per square yard or meter, around 6 pounds (3 kg) usually is enough. For raised gardens and garden boxes, it should add up to ½ inch (1.5 cm) of topdressing at the top.
  • If you’ve got shrubs and plants growing there, don’t add soil right near the crown. Stay about an inch away from the stem or trunk on all sides.
  • Water lightly, enough to moisten the topdressing but not flooding the bed. Too much water would displace the layer of topdressing and make it uneven.

Topdressing in such a manner is best repeated every three or four years. You can complement topdressing with a layer of plant mulch. Plant mulch is ideal for raised beds because it breaks down and continuously releases nutrients.

When the garden box is full, which may happen after 4 to 6 years, you’ll have to go for soil replacement. This is similar to what is described just above for topdressing houseplants.

The crown is the part of a plant where stem meets roots. It is where many exchanges take place.

Topdressing precautions

There are a few points of caution regarding this technique.

Delicate hands – When rummaging around in pots, tools will often wound roots. This raises risks of infection and root rot. Use your hands to work the soil when working on houseplants.

Poor topdressing – the goal is to replenish nutrients. Best is to use rich materials like compost. Sometimes potting mix is too poor. For example, you shouldn’t use seedling potting mix because there are very few nutrients in it.

Which topdressing is best

For most purposes, mature compost is the best topdressing.

Other possibilities include:

Sand – this is almost exclusively used as a lawn topdress, and then again mostly on golf turf. You may include it in your topdressing mix (up to a third) if you need to increase drainage, but don’t repeat it too often. Prefer coarse sand to fine sand. Never use sea sand, only river sand or quarry sand.

Manure – manure provides very rich nutrients. Depending on what the animals ate, though, you might notice weeds growing out of it (especially grasses).

Smart tip about topdressing

Topdressing is an excellent organic option to maintain your plants. You don’t need to add any chemical fertilizers because nutrients are replenished with fresh soil.

Read also

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Raking topdress on lawn by Rosalyn & Gaspard Lorthiois, own work
Large heavy container needing topdressing by Tanuj Handa ★ under Pixabay license
Working hands by Gabriel Jimenez ★ under Unsplash license
Crown of a plant by Robert Owen-Wahl ★ under Pixabay license