Mulching: What, Why, When?

One of the most impressive sights to see in winter is a weed free, well-tended border that’s nicely cultivated and mulched. How we prepare our borders in the winter is often the deciding factor of how well the summer will go. Much of the work in a border is best done in winter months, leaving only staking, weeding and dead heading for the summer (and perhaps watering in other parts of the country).

Mulching is a really important part of the garden calendar – it can be hugely beneficial, but in some cases can cause problems. We’ll get into that later… First of all, let’s tackle what mulch actually is, although quite frankly this is always up for debate. In my view, it’s something you put on top of the soil to suppress weeds and/or improve soil quality. Gravels and aggregates can be used as weed suppressants, but it’s more common to use organic matter (AKA, compost).

Parterre bedding since mulching

So, what do mulches do? Well, that depends on the type. Gravels and aggregates merely suppress weeds whilst keeping the soil cooler in summer and warmer in winter. Organic matter, however, is very different; it improves soil by making it more moisture retentive but also free draining. A complex gardening term which simply means it improves the soil’s structure and drainage. Generally, we want our soil structure to be like a sponge holding water and air, and organic matter is one of the best materials you will find for achieving this.  It also increases the activity of microbes in the soil and reduces compaction, so it does a lot of good with the help of worms doing their job and mixing it in to the existing soil.

At Aberglasney, we also use organic matter to protect the more tender plants from frost damage and to help drain the heavy clay.

Dahlia and Calandula bedding display where plants are mulch better since soil improvement

So, what’s the best organic matter to use? The two most important factors are that it’s well-rotted and weed free. Homemade compost is very good, but you’ll find it often has weed seeds in it. Well-rotted wood chip or shredding makes a very good weed suppressant but it takes a long time to rot down. Peat is often used but is extremely expensive and terrible for the environment – thankfully, it can be easily substituted.

Aberglasney’s Compost Heap

We’ve found compost waste from the local tip to be very effective at Aberglasney this year. We’re lucky to have many other good materials available to us here, including composted bark which is one of our favourites and we use large amounts of annually. Basically, it’s the best weed suppressant we know of and does a wonderful job of retaining moisture. It’s been particularly helpful in the recent dry spells we’ve been experiencing.

It’s important to know what plants need mulching and which don’t. For example, Peonies don’t like being mulched over but do appreciate it in the surrounding soil. A simple way to get around this is to put a bucket around the crown of the plant whilst you mulch and then remove it afterwards.

Cyclamen coum growing well in a nicely mulched border

One big thing to remember is that most mulches are alkaline and will raise the pH of your soil, so it’s always worth getting it checked before putting it on ericaceous (acid loving) plants. Bracken mulch is usually the best for this job. It’s made specially as ericaceous compost and you can buy it in most garden centres. It should be quite safe as the bags state their pH on them so you’ll know exactly what you’re using and whether it’s right for your garden’s needs.

As a rule of thumb at Aberglasney we mulch everything to a depth of 50mm and aim to do it biannually where appropriate. We often put a deeper covering on places with sandy soils where drought can be a problem, however, it’s important not to bury plants or to bank mulch up against the stems of shrubs and trees.

Jubillee woodland in spring as the plants push through the mulch

Mulching can be done at any time but it’s often best done in autumn or early winter so you can get the benefit of frost protection, plus it’s much easier to apply when the plants are cut back. Mulches have numerous benefits, can make life much easier and will help plants to give a better display when their moment of glory arrives.


Tips for the Week:

  1. Get mulching!
  2. Put out bird feeders to attract these handy garden predators
  3. Check plants are properly protected ready for the imminent cold spell
  4. Plan your veg garden and seed planting schedule if you haven’t already done so
  5. Christmas is a great time to browse catalogues and choose annuals for next year
  6. Planning which gardens and shows you’d like to visit next year will always help to lift the spirits and give you something to look forwards to at this time of year