The Mulch Chronicles- Part 3
We’ve discussed different forms of mulching for commercial or large home scale growing but what about backyard dahlia growers?
Mulch by definition is just a layer of material applied to the surface of the soil. So therefore mulch can be many different things— straw, pine straw, bark, rocks, landscape fabric, grass clippings, shredded leaves, newspaper/cardboard, etc.
They all have pros and cons and we’ll get to those in a bit but first— what are you looking for in a mulch?
Most of the time, we want weed suppression and moisture retention from mulch and if it’s an ornamental garden, we’d like it to look nice too.
Also it’s worth remembering that mulch will decompose (unless it’s an inorganic type -rubber mulch, landscape fabric, etc.) So you will have replenish it - yearly for most types of organic mulch. This is important to note and remember. Mulching is not a do it and then assume you’ll never have to again type of job. Keeping it topped up is one of the best ways to avoid hours on your hands and knees weeding!
Let’s take a look at the most common types of mulch:
1. Pine straw— this one is popular (evidenced by the number of you who emailed me asking about it). Pine straw is a very commonly used mulch - especially in Southern states because we have lots of pines. It’s easy to source, affordable and weed free. Lots of good points but nothing is perfect. Pine straw has the tendency to move around in a heavy rain/wind storm. Also due to it’s nature (skinny long pieces), it’s weed suppressing capabilities aren’t the strongest. It’s slow to decompose - which is a pro and a con. Pro because you may not have to replace as often, con because it’s not adding organic matter to your soil as quickly.
2. Bark- Definitely one of the best looking mulches for landscape situations. Adds nutrients to your soil as it breaks down. It has a reasonable decomposition rate— by that I mean it’s not super slow but not fast either. You’ll lose a small percentage the first year and it’ll increase after that if you don’t top it up. A 4-5” layer of bark mulch will suppress a lot of weeds though! Be careful about using bark mulch that’s been sitting open to the environment for awhile- it can harbor weed seeds. If you are buying by the truckload, cover it or use it up quickly so it doesn’t turn into a weed seed repository. I have found that when using bark mulches with heavy clay soil that it tends to add to the “heavy” factor of clay soil. I recommend adding compost before you lay down your bark mulch. This will keep your soil from becoming too heavy.
3. Rocks- For a permanent planting, these can look great. Probably not ideal for dahlias though. Since there is the potential for having to dig the dahlia, I wouldn’t recommend rocks as a great choice.
4. Grass Clippings- First off you want to make sure your clippings haven’t been treated with anything that could harm your dahlias. Make sure you know what’s on that grass! Also be careful not to apply them too thickly and they can mat and prevent air flow and too much moisture retention around your plants. They are a valuable source of organic matter for your soil though. I would apply clippings in a thin layer and then apply another type of mulch on top.
5. Shredded Leaves— Leaves are the gold standard for adding amazing organic matter to your soil. I was lucky to get a free dumptruck load of aged leaf compost at my farm many years ago. I can still tell where that compost was added because the soil is noticeably better there. Nice thing about leaves is that you should be able to get them for free. You’ll need to think ahead for the next season and collect in Fall. If you have a shredder, even better. Or just run a lawnmower over a pile of leaves. The smaller pieces will break down quicker.
6. Newspaper/Cardboard- I definitely wouldn’t call these stand alone mulches but they are useful tools. If you are dealing with an especially heavy weed load, applying a layer of paper/cardboard will really help to keep the weeds down. Cardboard plus 6” of bark mulch will keep weeds at bay for quite a while. It’s a good tool for an especially weedy area.
There are plenty of types of mulch out there— My thoughts are— use what’s plentiful in your location, easy to acquire, affordable and will keep weeds down and moisture retained!
