By: Anne Baley
If you’re not using mulch in your vegetable garden, you’re doing entirely too much work. Mulch helps to hold in moisture, so you don’t have to water as often; it shades out weed seedlings, cutting down on weeding time; and it composts into nutrients and amendments for the soil. It’s clean, it’s light and it breaks down relatively easily, giving your plants more of what they need to grow. Let’s find out more about using straw mulch for gardening.
The first key to using straw as mulch is in finding the right types of straw garden mulch. Some straw mulches may be mixed with hay, which can weed seeds that can sprout in your garden rows. Look for a supplier that sells guaranteed weed-free straw.
Rice straw is very good, as it rarely carries weed seeds, but wheat straw mulch in gardens is more readily available and will work just as well.
How to use straw mulch in the garden is easy. Bales of straw are so compressed that you might be surprised at how much of your garden one bale will cover. Always start with one and buy more if it’s needed. Place the bale at one end of the garden and clip the ties that run around the bale. Insert a trowel or sharp shovel to help break up the bale into pieces.
Place the straw in a 3- to 6-inch (7.5-15 cm.) layer in between the rows and between the plants in each row. If you’re growing a square-foot garden, keep the straw to the center aisles between each garden block. Keep the straw away from the leaves and stems of the plants, as it may spread fungus to your garden crops.
Straw will compost pretty quickly in most garden settings. Check the depth of the layer in between rows after about six weeks. You’ll probably need to add another layer, to the depth of 2 or 3 inches (5-7.5 cm.), to help keep the weeds down and moisture in the soil during the hottest part of summer.
If you’re growing potatoes, straw is the ideal way to hill the area around the stem. Usually when gardeners grow potatoes, they hoe the soil around the plant and pull loose soil into a hill around the potato plant. This allows more potato tubers to grow along the stem underneath the soil. If you pile straw around potatoes instead of hilling up the soil, the potatoes will grow cleaner and be easier to find at the end of the season. Some gardeners avoid using soil at all for their potato plants, and just use successive layers of straw added throughout the growing season.
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The coarse texture of straw helps it trap air, which provides soil insulation and protects the garden bed from temperature fluctuations. The straw is also porous and allows moisture to seep down into the soil, notes University of California Sonoma County Master Gardeners. Like most mulch materials, straw helps conserve soil moisture and prevents rapid soil drying and drought stress.
Using straw to kill weeds is also effective, as it suppresses most unwanted plants so they can't grow and establish in the bed. Straw keeps developing fruits clean, especially vine varieties like melons, tomatoes and squash that usually sit directly on top the soil.
First, let’s outline the key benefits that pine mulching offers over other materials.
I’ve spent my share of weekends shoveling bark mulch and rocks for flower bed covering. I will concede to this one. Pine straw is much lighter and easier to work with than most other mulching options. It can be a little irritating with the needles sticking you as you work it but compared to shoveling heavy piles of bark, yeah, pine straw wins this one.
A thick blanket of pine straw does an excellent job of maintaining moisture levels. That is one of the key benefits that pine tree needles actually provide for the soil in the forest (source).
This is not to say that pine straw holds in moisture more effectively than bark mulch. But it is fair to say that it can hold its own in this area.
Pine straw is known to decompose at a slower rate than many other carbons. The selling point here is that it takes longer to break down than bark mulches and therefore, in theory, should last longer before replacement is needed.
This is probably the greatest single appeal of pine straw as a mulch. Many people like myself live in an area where pine trees continuously blanket the ground with a fresh supply of potential mulch.
The idea of free mulch is certainly an appealing one and depending on your situation this may be the deciding factor for you.
Before you go all-in, however, let’s balance these benefits with a few of the less-wonderful aspects of this mulching material.
There are two cardinal rules for using mulch to combat weeds. First, lay the mulch down on soil that is already weeded, and second, lay down a thick-enough layer to discourage new weeds from coming up through it.
A four-inch layer of mulch will discourage weeds, although a two-inch layer is usually enough in shady spots. If you know that a garden bed is filled with weed seeds or perennial roots, try a double-mulching technique to prevent a weed explosion. To do so, set plants in place, water them well, spread newspaper, and top it with mulch.
Mulches that also retains moisture (like wood chips) can slow soil warming. In spring, pull mulch away from perennials and bulbs for faster growth. A wet mulch piled against the stems of flowers and vegetables can cause them to rot keep mulch about one inch away from crowns and stems.
Mulch piled up against woody stems of shrubs and trees can also cause rot and encourages rodents (such as voles and mice) to nest there. Keep deep mulch pulled back about six to 12 inches from trunks.
The straw that I’ve been using for years in my garden is EZ-Straw Seeding Mulch. It’s organic biodegradable straw that is processed and free of weed seeds.
This is just an example of what I use, but there are many other options available. The important thing is to make sure that the straw you’re getting is certified weed-free.
Nothing is worse than bringing something into your garden that will do it harm or cost you more work. And I can tell you from experience that I’ve made many mistakes in my years of gardening, but I’ve learned from them. The lesson that I’ve learned is that you should never take the chance to bring something into your garden that you’re not 100% sure of. You could end up regretting it.
Find out about mulches and how to mulch, in our expert guide.
Published: Monday, 25 January, 2021 at 8:51 am
Mulch is a thick layer of material placed over the soil and around plants, used to suppress weeds and lock moisture into the soil, while acting as a physical barrier to drying winds and direct sun. Some mulches also contain nutrients, acting as slow-release plant food. As worms take the mulch into the soil they help to improve soil structure, making it more moisture retentive, free-draining and fertile.
Organic mulches also contain nutrients, acting as slow-release plant food. What’s more, while they’re breaking down they attract beetles, worms and other soil invertebrates, which provides food for birds.
Find out more about mulches and mulching, in our guide, below.
There’s a wide variety of mulches to use – both organic and inorganic – which have different uses in the garden. Organic mulches are made from dead plant material such as compost, leaves, bark or grass clippings. Inorganic mulches include rocks or gravel but they can also include plastic sheeting, landscape fabric and ‘rubber mulch’. Unlike organic mulches, inorganic mulches do not break down. Indeed some, such as plastic sheeting, can disintegrate over the years and pollute your garden environment. Inorganic mulches don’t add nutrients to the soil and can, in some instances, stop nutrients reaching soils. However they can offer a more long-term solution to weed suppression than organic mulches.
Organic mulches include:
Leaf mould – low in nutrients but an excellent soil conditioner, leaf mould provides a quick reward for a little effort. Simply bag up leaves in autumn and they should be ready to mulch around your plants after around 12 months.
Well-rotted horse manure – this is packed with nutrients and retains moisture well. It’s excellent for mulching around hungry plants like roses and edibles, especially pumpkins and squashes. Make sure it’s been left to rot for at least two years, otherwise it can ‘scorch’ plant leaves and even remove nutrients from the soil as it breaks down.
Homemade garden compost – this is is a fantastic all-round mulch, great for retaining moisture, suppressing weeds and improving soil. Add kitchen scraps and chopped up garden waste to your compost bin and turn every few months. You should have a useable compost between six and 12 months later.
Composted woodchips or bark – this bulky mulch breaks down slowly and is ideal for improving soil structure by improving drainage and making it more moisture retentive. Also, its dark colour makes offsets the green of plants beautifully.
Mushroom compost – often bought as ‘spent’ mushroom compost, this alkaline mulch is light and easy to use. Given its high pH, it’s ideal for lime-loving vegetables, including brassicas like kale, cabbages and broccoli. Avoid using on lime-hating, ericaceous plants like rhododendrons, camellias and heathers.
Want to know more about organic mulch? Watch our No Fuss video guide, where David Hurrion reveals some of the basic forms of organic matter, including rotted horse manure and home-made compost, and explains where they’re best used:
Inorganic mulches include:
Rocks or gravel – rock or gravel mulches are typically used in gravel gardens, and can help seal moisture into the soil and suppress weeds. Bear in mind that rock or gravel mulches can heat up in the sun and cause the planting area to become too hot for many plants to grow. They’re best used in drought-resistant planting schemes.
Plastic sheeting or landscape fabric – this is laid over the soil and suppresses weeds. Some fabrics are better than others. Bear in mind that some will disintegrate over time and leach plastic fragments into the soil and surrounding environment. It’s also thought that impermeable sheeting also stops rain, air or nutrients reaching the soil, which makes it a bad option for using around plants, which need water, nutrients and air to live.
Rubber mulch – made from recycled tires, rubber mulch can suppress weeds and breaks down naturally, albeit very slowly. However, it’s not clear how toxic rubber mulches are. Potentially material from old tyres could contain a number of harmful chemicals from the road that could leach into your soil.
The best time of year to mulch is spring and autumn, although April is the ideal time to mulch with organic compost as the soil is moist and accessible, and plants are just starting into growth.
Applying compost is easy – simply lay 5cm of your chosen mulch onto the bed or around key plants, without smothering them or damaging the lower stems. Bear in mind that a really thick layer of mulch will suppress more weeds, but bulbs and other plants will find it hard to grow through more than a 5cm layer. Use your hands or a spade to add the mulch, depending on the material you choose. Finally, use a rake or hoe to make sure the mulch is evenly distributed.
When applying mulch, it pays to prepare the soil beforehand. This will save you time and effort in the long run:
Around spring bulbs – mulching around spring bulbs as the foliage dies back will feed the bulbs and lock in moisture just when they need it. Mulching will also reduce the need for digging, which can easily lead to bulb damage.
Under hedges – apart from regular clipping, hedges are often ignored. Their roots are packed together, and benefit from an annual mulch to lock in moisture and feed the plants. Make sure the soil is moist or water well before mulching.
Around herbaceous perennials – dark organic mulch visually sets off herbaceous perennials. If you’ve just divided and watered them, then mulching around the new plants will give them a boost as the growing season gets going.
Around fruit trees and bushes – fruit trees and bushes need plenty of moisture around their roots, especially when fruit is forming. A regular mulch will suppress weeds and help keep the plants healthy and resistant to pests and diseases.
You can make your own mulch by composting kitchen and garden waste. You can also make your own leaf mould. If you have access to a local stables you can buy (or be given) horse manure which you can pile up to rot down (make sure all animal manure has rotted down for at least two years otherwise it may scorch your plants).
Problems with mulching occur usually when you’ve mulched too thickly, which prevents bulbs and herbaceous plants from growing. Gently use a rake or long-handled cultivator to gently thin out the mulch, which may help plants grow better.
Here, Kevin Smith, BBC Gardeners’ World Magazine, explains which bulbs grow through mulch and how deeply to mulch your soil:
Another problem you might experience is when using manure to mulch plants. If this isn’t well-rotted it can scorch plant leaves and even lead to the, becoming distorted.
Some types of inorganic mulch can disintegrate into the soil, heat up the planting area and potentially leach harmful chemicals into the soil.
The quality of your mulch depends of the quality of the straw you use. If your straw is contaminated with weed seeds, you will be planting weeds when you mulch. If the straw is contaminated with herbicides or pesticides, you will be adding those to your garden as well. Get clean straw without any dampness or mold. Open the bales and spread the straw about 2 inches deep around your young plants. You can leave the mulch through the winter to help minimize erosion. Some gardeners remove the mulch the following spring and add it to the compost pile. They start with new straw with the new spring crop. Other gardeners, especially those who practice minimum tillage, simply fluff the old mulch in the spring and add new straw to bring the level to 2 inches. In general, if the mulch is getting moldy and you are worried the mold will spread to the plants, remove the mulch.
Straw is composed mainly of carbon. Breaking down high-carbon plant material requires nitrogen. Plant growth also requires nitrogen. If your soil has too little nitrogen to begin with, your plants can actually be robbed of nutrients rather than fertilized by the straw mulch. The solution is to supplement. Nitrogen-rich chemical fertilizers are, of course, a possibility. Grass clippings, however, are also rich in nitrogen. So are aged manure (especially chicken manure), worm castings, clover and coffee grounds. If you compost, or even partially compost, the straw with any of these high-nitrogen ingredients before mulching with it, your straw won't rob your plants of nitrogen.