The key to getting a luscious flower bed starts with the growing medium. That’s a fancy way of referencing what you grow your plants in. But how do you choose the best compost for flower beds? And what makes a good compost to begin with?
For most plants, the perfect soil starts with loam. That’s a combination of sand, clay, and silt. The sand helps keep the soil loose with its larger particles. Clay helps with water retention. Silt frequently provides the nutrients.
Amendments help you take great soil and improve upon it. That includes compost. People like to use the words compost and soil interchangeably as if they are the same thing and they aren’t.
Soil is whatever combination of silt, clay, and sand you have on hand. Compost is something you add to it to give it a bit more body and in many cases additional nutrients.
Most compost is comprised entirely of organic matter like shredded tree bark. You might even have a backyard composter full of grass clippings and leftover food. While there is some organic matter in soil, also, soil is mostly inorganic minerals.
Although compost can contain a lot of nutrients, it’s also not the same thing as fertilizer. You can reduce the need for fertilizer by adding it, but it isn’t a suitable replacement.
Adding compost to packed soil will help keep it loose. It will also encourage the development of bacteria and fungus in the soil necessary for the development of humus, the richest growing medium there is. It also helps with moisture retention.
There are some good, generalized composts available. But, if you’re growing flowers in a bed, there are composts available specifically designed for those. While you can add generalized compost to flower beds, you’ll get your best results if you match your compost to your soil and provide a growing medium perfect for your needs.
Here are some composts we think are among the best for use in flower beds. As a side note if you are looking for the best soil type for vegetables, we made a list for that too.
Best Overall: Livestock manure
The best compost for flowers comes right from the farm. It’s livestock manure.
It does it all. It helps stimulate the growth of beneficial bacteria and fungi under the ground, creating a healthy micro-ecosystem. It aids in water retention and helps keep soil loose. Because we eat a lot of meat, it is also really pretty affordable.
Manure’s biggest plus is how it adds nutrients. Grass-fed animals produce manure with higher nutrient loads than do grain-fed animals. But both add plenty of nitrogen that is necessary to stimulate foliage growth.
It’s also easy to add to your soil. Before you prep your beds for planting — either tilling or turning the soil — spread a thin layer of it across the entire bed. When you work the soil, it will naturally blend in.
There are a couple of things you should know before using it, however.
The first is that, unless you know what you’re doing, you should only get commercially prepared manure compost. Manure itself, especially that from chickens and other birds, is so nutrient-dense that it can damage plants the same way that overfertilizing plants with chemical nitrogen will burn them.
Commercially available manure is always cool enough to use on your plants. You can also check to see how much of each nutrient the manure you’re buying has.
The other is that while it can assist in water retention and soil compaction, it is not ideal for those. If your beds dry out too quickly, have a lot of clay in them, or are just really compacted from years of use, you might want to blend in another amendment to help with those.
It’s also organic, which means it will eventually break down and need to be replaced.
Runner-up 1: Worm castings
Worm castings are one of the best composts available for any plant, and especially in flower beds. Worm castings are what worms produce when they eat vegetables. So, it’s basically worm poop.
Among composts, worm castings contain some of the highest levels of nutrients. We ranked it our first runner-up in large part because it just doesn’t provide the level of nutrients that livestock manure does.
If you are not tied to the idea of using just one kind of compost, worm castings blended with mushroom substrate create one of the best one-two composting punches there are.
Worm castings do a better job than livestock manure when it comes to water retention and a similar job when it comes to breaking up dense clay-heavy soil.
Among the composts we looked at, it’s also one that you can make yourself. It will require some equipment and work, but you can do it.
Beyond its lower nutrient load than animal manure, it’s also really expensive. It’s the most expensive soil amendment of the ones we looked at. You can probably find animal manure for a lot less money.
Runner-up 2: Mushroom compost
Mushrooms sold in the grocery store are grown not in soil but a crafted growing medium. It blends manure, gypsum, and straw.
The biggest benefit is that the straw helps to break up dense soils, especially clay. If you have pots or raised beds, the mushroom substrate is useful to add every couple of years to help reduce compaction.
It can also hold onto a lot of water. That also makes it ideal for raised beds and pots, where the soil can dry out quickly. It also has some application in sandy soil, where water retention is a serious problem.
It can almost hold on to too much water. If your soil has a heavy silt component, you might wish to avoid using the mushroom substrate as a soil amendment to avoid waterlogging your soil.
The actual mushrooms grown in the substrate tend to leach out most of the manure’s nutrients, so it isn’t great when it comes to reducing your need to use fertilizers. What nutrients it does contain will slowly add to the soil, which you’d expect from an organic soil amendment.
Like other organic soil amendments, it will also break down over time.
Runner-up 3: Peat moss
There are two things that peat moss has going for it as a soil amendment: It is very loose and it absorbs a lot of water. That will reduce the soil compaction problems in raised beds and pots.
If you need a soil amendment to address a compaction problem or just need something to boost water retention, peat moss is a great option.
If you’re starting your plants from seeds, we’d highly recommend it as a base. It allows young roots to easily spread and holds lots of water, which helps seedlings stay damp. It also doesn’t have a ton of nutrients, so while you’ll need to add a little fertilizer you won’t risk killing plants by burning them with nitrogen.
Something you’ll want to keep an eye on is the ph level. Peat moss is slightly acidic, so while that’s great for plants that like soil that way you might need to balance it out if your plants favor an alkaline environment.
If you like compost for an added nutrient punch, peat moss has very little of it. Again, it’s a little incomplete for our tastes to serve as a standalone compost. That is especially in a flower bed where the plants tend to feed heavily.
It’s also organic, which means eventually it will break down and you’ll need to add more. This is the same with all the composts we’ve looked at. But it is worth keeping it in mind.
Prevention and treatment of powdery mildew
One of the most common garden problems is powdery mildew. It can come seemingly out of nowhere. One day, your plants are clean, the next they are covered in it. Left unaddressed, it can wipe out your plants in short order.
So, how do you address it? We’re here to help.
The first thing you’ll want to know is that powdery mildew isn’t a single species of fungus. It’s a whole family of them.
The different species will also target different plants. The powdery mildew that can turn your summer squash into a wilted mess won’t touch most flowers, but those flowers have their own powdery mildews that will tarnish their leaves. Those will ignore your summer squash.
You can get an exhaustive list of plants that are affected by different powdery mildews, and which species target what.
Preventing powdery mildew from taking over your garden beds starts with prevention, which means knowing how powdery mildew takes hold.
Unlike most fungi, powdery mildew prefers conditions that are a little cooler and a little drier. Most people associate mildew with warm, damp conditions.
You’ll want to keep your plants pruned and the ground beneath them as free as clutter to allow air to flow freely between leaves to blow away spores in the air.
Also, moderate the amount of water you use and keep it as close to the ground as possible. Like most fungi, powdery mildew can splash up onto plants by water that hits the ground. This will also help you reduce other sources of fungal infection.
Give a thorough watering whenever the soil gets dry and do it in the morning. Watering in the afternoon can cause sunlight to shine through the beads of water and scorch plant leaves the same way that a magnifying glass can burn ants.
Watering at night allows moisture to stick around under leaves all night. While this won’t necessarily keep powdery mildew at bay, it will reduce other fungi from spreading.
You can also administer a preventative treatment of copper fungicide. This is best used before the mildew appears. Other, more natural preventatives include spraying baking soda on your plants.
If you wind up with an infestation, eradication is unlikely but you can manage it. First, trim any infected parts off. Burn them if you can. If you can’t dispose of them in the garbage. Don’t attempt to compost them.
You can apply some apple cider vinegar to kill some of the mold. Be careful how strong a concentration you use, however, because the vinegar can also kill your plants.
The most important thing is to not get frustrated and give up. Think ahead to the next growing season, too. If you plan to use plants previously infested with it, place them in a different location. Rotating plants around is a good idea, anyway.