We all love trees, and we all need them. So growing, planting and looking after trees in our yard is fundamentally important. But what part does compost play in this process?

Compost is good for trees at all stages of their development. From growing saplings in pots to planting out young trees, and then to providing mulch for mature trees – compost is an excellent way to nurture trees from ‘acorn to oak’.

Let’s dive down into this subject in more detail. We’ll discover why compost is good for saplings, young and mature trees – and consider whether we can ‘over-use’ compost in a harmful way at any stage of a tree’s lifecycle.

Why is Compost Good For Both Young & Mature Trees?

Compost is extremely good for trees. It’s made from rotted down organic matter, so replicates the natural forest floor, making your trees feel at home. As well as providing nutrients, compost helps the soil to stay at the right temperature, and reduces moisture loss.

What is the best type of compost to use for trees? Mature, home-made compost is always good, and it’s a marvelous way to recycle your scraps into something that benefits your yard.

Otherwise, you can buy a good organic compost at the garden center. Make sure the compost you buy has a light and fluffy texture. You can test this by picking up one of the bags. If it feels heavy or lumpy, this isn’t quality compost.

Some neighborhoods have set up community compost schemes: do an internet search for your local area to see if there’s one near you. Also, take a look at the US Composting Council’s website, for details of local businesses (such as farms) that have certified compost to sell.

You can add compost to the soil when you’re planting a sapling or young tree, then keep mulching the tree as it grows. Here’s how to safely use compost to enrich the soil around your trees.

How To Use Compost For Potting Tree Saplings

If you have a sapling to plant in a pot, it’s especially important that the delicate young tree has the right nutrients. After all, it won’t be getting anything from the soil, so you need to come up with some substitutes for its natural growing environment.

Unless it’s specifically grown as a container plant, a young tree shouldn’t be in its pot for longer than a year. When you’re putting the sapling or seedling into its first pot, select one that’s bigger than the root system, and that has good drainage holes.

Soil alone is too heavy for these delicate infant roots, and it’s unlikely that a bucket of dirt from your yard will have sufficient nutrients for your baby tree. Mix soil with organic compost for a lighter, nutrient-rich blend. You’re searching for a compost that’s suitable for nursery use so won’t be too dense for new roots.

If you’re using a fertilizer, choose one that slowly releases its nutrients, rather than dumping them in one big hit, which can be overwhelming for the sapling.

When it’s time to move your sapling from the pot to its permanent home in your yard, make sure the soil is prepared for it by adding some compost. This next section takes you through using compost when planting young trees.

How To Use Compost When Planting a Young Tree

When you’re planting a young tree, adding compost to the soil will give it a lovely, nutritious start to its new life in your yard. Compost is denser than soil, so mix it with soil then spread it over a wide area. Also, simply placing the compost in the hole you’ve for the tree could discourage the roots from pushing out any further.

When you’re planting a young tree directly into the ground, first work out what its drip line will be. The drip line is the parameter of its canopy. So, stand the tree on the ground, either in its pot or held up by a second person, and using a spade or stick, draw a line on the soil to mark the drip line. This is where you’ll need to compost.

Rake the soil in this area to break up any lumps and aerate it. Then, starting slightly away from the trunk, work in a layer of compost into the top two inches or so of the soil, right up to the drip line. Don’t compost right up to the trunk itself as this can attract pests or even rot the delicate young wood.

You can repeat this about twice a year to help keep the soil in perfect condition for your growing young tree. Make sure you’re very gentle when you prepare the soil, as there will now be roots between the trunk and the drip line.

How To Use Compost As a Mulch For Mature Trees

The tree never grows out of its need for nutrient-rich soil, so the regular application of compost is a must. A good way of doing this is to use your compost as a mulch.

A mulch is a layer of material that’s added to the top of the soil. It’s full of goodness for your plants, providing them with nutrition and moisture, with the added benefit of keeping the weeds down. A layer of rich, dark mulch also makes an attractive finish.

Using home-made compost or good-quality, store-bought organic compost, prepare the soil from the “root flare” (where the trunk ends and the roots begin, so, just a bit away from the trunk) up to the drip line.

Once the soil is prepared, evenly spread the compost throughout this area, at a depth of between two and four inches. Use a rake to make sure it’s covering the whole area.

Then – do nothing. Nature will look after your compost layer, as rain will dampen it down and those busy earthworms will help work it. If no rain is forecast, water in the compost. If you want to add another decorative mulch such as husks, wait a few days after composting to add a layer. However, in most cases, the compost mulch should be enough.

As we mentioned earlier, don’t mulch right up to the trunk as this can harm the tree. We’ll take a closer look at the problem of “volcano mulching”.

Can You Damage Growing Trees With Too Much Compost Mulch?

Yes, you can. The main problem is caused by a build-up of compost mulch against the tree trunk or exposed woody roots. Piling up compost against the trunk is sometimes called “volcano mulching”, and it’s a big no-no in the world of arboreal gardening. The large pile of rich and tasty compost attracts bugs, who after chowing down on the tasty matter, will simply move onwards into the tree.

This cool, damp pile of compost is also perfect for fungus (and not all fungi are welcome tenants) as well as causing serious problems such as disease and rot. So, spread your mulch out, mix it with soil, and never take it right up to the tree trunk.

You can also have too much of a good mulch. Too generous a dose of compost isn’t good for plants, and many gardeners will recommend a typical 70/30 mix of soil to compost.

Problems caused by too much compost include smothering young growth, and encouraging the plant to grow too quickly. If there’s too much compost in a small area, it will compact and potentially cause issues with watering and drainage.

So when you’re planting your young tree, as we briefly mentioned earlier, don’t fill its hole with compost. This prevents its roots from reaching out into the native soil, forming a strong anchor for the growing tree. The roots are so happy in their compost-rich hole, that they simply stay there and don’t grow outwards like they’re meant to.

Summary

So the great news is that compost is very good for trees at all stages of their development, provided it is applied properly (see volcano mulching above) – and this is good news for all of us.

From potting saplings and planting out young trees – to helping older trees to grow – compost is beneficial for trees ‘from acorn to oak.

And of course, when you grow, plant and nurture trees from saplings to more mature adults – it might be years in the making but you’re doing something great for the whole environment and having a positive impact on all our lives. 🙂