Common Raised Bed Garden Questions Answered

Raised beds are one of the absolute BEST ways to grow a garden but there can be challenges to growing in raised beds. Often gardeners have questions about the best methods to grow in a raised bed. In this post I’ve taken some common raised bed garden questions and put together some answers based on my experience. I’ve grown in raised beds of some kind my entire gardening life and for small scale gardens, backyard gardens, and home gardens they are amazing options for gardening. Let’s get to answering some of the most common questions about raised beds.

What are the best materials for raised beds?

Raised beds are commonly made of an untreated type of timber. Pine has the advantage of being cheap and readily available but will decay much faster than other materials. Cedar is commonly recommend as being more rot resistant but is more expensive.

cedar raised bed with seating bench
Cedar Raised Bed with Bench side

The best materials are usually ones that are easily attained without a huge cost. No matter what wood material you choose it will eventually rot so you could consider stone and concrete blocks. Those tend to be more permanent but are on the more expensive side. I’ve grown in timber/lumber raised beds and concrete and between the two types I think I prefer the timber. It’s easier to put together, lumber will last at least 2 to 3 years in the garden, and if you design them right can look really nice.

Another alternative that I’ve use before is trunks and large branches of trees. As long as they are straight enough to form sides you can make a nice rustic raised bed!

I wrote another post on the Best Materials for Raised Beds that you should read if you have more questions on material choices for raised beds.

How deep should a raised bed garden be?

The best depth for a raised bed varies depending on many things. If the soil is decent to begin with then a raised bed as low as 4 inches would be fine. Essentially you would be creating a method of containment for the soil to stay in the bed and adding a rich compost to topdress the existing topsoil.

If the soil is poor with heavy clay or lots of rock then a taller raised bed is better. I would recommend at least 12 inches tall with poor soil underneath.

hexagonal raised bed made of cedar
These cedar hexagonal raise beds are set at different heights.

If you are wanting comfortable height raised beds to be able to walk around them then measure to just below your waist and build raised beds close to that height. 3ft tall may be a good guideline without making them too tall. The taller you make a raise bed the more soil you have to fill it with and for taller crops it may put some of the produce higher than you would like to reach. For extra height you can build your raised bed with feet and a bottom to make a planter box.

How deep should a raised bed be for tomatoes?

See the previous question for a general depth of raised beds but for tomatoes I would want to have a reliable 8-12 inches of good soil underneath them. 16 to 24 inches would be better but if you are building a raised bed for tomatoes on the ground and the soil isn’t bad underneath then you could get away with 6 inches or so for your raised bed height.

Should I Line Raised Beds?

Maybe. If you are using a pressure treated lumber and are concerned about chemicals leaking into the soil line them. Also if you are using an untreated lumber lining the beds will help the wood last longer and reduce the need to replace them as often. Is lining a bed absolutely necessary? If you are OK with needing to replace the beds every few year then it really isn’t necessary to line the beds.

What should you line raised beds with? Ideally a pond liner or similar material is good for keeping the moisture in the raised bed.

Should I put plastic under my raised garden?

NO WAY. Plastic under a raised bed can become a drainage issue. Plant roots need to breathe and the plastic will hold water which could drown them. Don’t put any plastic on the bottom of the raised bed. If you have already done that and planted the bed then puncture the plastic to allow drainage holes to release the water. Then remove the plastic next time you have an empty bed.

What do I put on the bottom of a raised garden bed?

As I just mentioned don’t put plastic on the bottom of your raised beds but you may way to put cardboard or thick layers of newspaper on the bottom. The biodegradable paper products will help smother existing weeds and grass that may be there and prevent them from emerging through your raised beds.

When setting your raised bed down you can lay the newspaper or cardboard layers directly on the grass and put the raised bed right over them. The grass will be smothered and it’s decay will become organic matter that your vegetable garden can eventually use to make you food!

raised bed vegetable garden with lumber
Simple raised bed made with lumber and planted with Lasagna Gardening techniques.

Also if you have issues with burrowing animals getting into your raised beds consider stapling hardware cloth or chicken wire to the bottom of the beds. This can help somewhat but may not prevent them completely. I generally don’t add any hardware cloth underneath my garden beds.

11 Tips for Designing a Raised Bed Vegetable Garden Layout

Should I put rocks in the bottom of my raised garden bed?

There really is no good reason to put rocks in the bottom of a raised bed. Rocks will take away space from valuable organic matter that your plants would rather have. Opt instead for a good layer of compost. Rocks may also make it harder if you ever needed to work the beds with a broadfork or small tiller.

Should I put landscape fabric under raised bed?

You can put landscape fabric under your beds if you want to but it isn’t necessary if you use the newspaper or cardboard layering method. The purpose of landscape fabric is to prevent weeds seeds from sprouting and growing up through the fabric. The newspaper and cardboard will do the same thing but eventually will break down in the soil. By then the beds will be thick enough that the weeds won’t be able to germinate an get to the soil surface.

What vegetables grow best in raised beds?

Almost all vegetables do well in raised beds! That’s why they are so great to use in your home garden. Here is a list of some great vegetable options to grow in raised beds:

  • Tomato
  • Pepper
  • Eggplant
  • Asparagus
  • Strawberry
  • Tomatillo
  • Potatoes
  • Squash
  • Zucchini
  • Onions
  • Shallots
  • Beets
  • Radishes
  • Carrots
  • Kale
  • Mustard
  • Pak Choi
tomatoes in the vegetable garden

How do you fill a raised garden bed?

To fill a raised garden bed you want to find a good well drained and rich soil medium. That can mean a lot of things like compost, Lasagna gardening, or even wood chips.

Use Compost to Fill a Raised bed

Compost is an excellent way to fill a raised bed with a caveat. You need to make sure that the compost is not fresh. Fresh compost often will have too much nitrogen and can either burn your plants or could encourage way too much leaf growth. If you have the opportunity to gather fresh manure from chickens, cattle, horses, goats or other farm animals take it but instead of using it directly in your garden let it age in a compost pile.

What is the best soil to put in raised beds?

The best soil for a raised bed garden is a rich blend of well aged compost! You can attain that simply by gathering compost materials in a compost pile and waiting for it to age properly. Compost/grow mixes can also be purchased at stores or landscape supply companies. Try to avoid buying soil mixes that have artificial fertilizers in them and lean toward organic/natural mixes if at all possible.

Can Wood Chips be used in a Raised Bed?

They can! They need time to full break down but if you have let them age for a little while you can fill your raise beds with them. Here’s a short video where I’m talking about using wood chips in my raise garden beds.

Do raised beds need drainage?

If your raised bed is a wooden frame and open to the bottom then you probably don’t need to improve the drainage. Your vegetable garden plants will need drainage but if your garden is open toward the bottom it will be fine. All plants need air around the root systems so having a raised bed that does not retain too much moisture is important for the roots to breathe and take up valuable nutrition from the soil.

Can you put raised garden bed on concrete? What about gravel?

You can place a raised bed on either concrete or gravel. The nature of a raised bed is the ability to add great soil. The main concern with a raised bed on concrete is that your bed needs to have enough depth to allow plenty of room for good root growth. That is easily adjustable by making the raised bed taller. Instead of a 6 inch high raised bed boost it to 18 or 24 inches.

The other concern I would have with putting a raised bed on concrete would be the heat island effect. The concrete absorbs heat and will keep that area warmer. That’s great in the winter but may not be great in the summer.

Do you have to change soil in raised beds?

You do not have to change your soil in a raise bed. What I recommend is to add compost to it every year. Adding compost combined with occasional fertilization will give your plants all the resources they need without the need to change out the soil in your raised beds.

If you end up with a disease that is a soil born disease then change what you plant in that garden bed and replace it with a member of another plant family that won’t be susceptible. An example of this is if your tomatoes start to get blight you may want to plant lettuce or onions in that bed and not grow tomatoes or peppers in that same bed for a couple seasons.

How many bags of soil do I need for a 4×8 raised bed?

To calculate the amount of soil you need to fill up a raise bed garden is a simple volume equation. Most bags of soil come in 2 cubic feet sizes. With that in mind multiply the

Length X Width X Height = Volume of Raised beds

For example a 4 x 8 Raised bed that is 6 inches tall would be:

4ft X 8ft X 0.5ft = 16 Cubic Feet

So since we need 16 cubic feet of soil we will need 8 2 cubic foot bags of soil to fill up that raised bed. If your dimensions are different just plug in the dimensions of your raised beds. It’s easy, you can do this!

How many tomato plants can I grow in a 4×4 raised bed?

I generally plan for a 2ft x 2ft area for each tomato plant. That’s 4 square feet. A 4 ft x 4ft raised bed then has room for 4 tomato plants. The problem with that is tomato plants love the sun. By putting 4 plants in a square raised bed two plants are likely getting shaded by the other two tomato plants. What might be a better strategy is planting 4 tomato plants in a rectablge raised bed in a row. A 2ft x 8ft raised is the same size but when oriented east to west will provide the maximum amount of sunlight for each plant.

raised bed vegetable garden made with untreated lumber with tomato plants

I would rather build larger raised beds with dimensions closer to 4ft widths and 6 or 8 ft lengths. Then I would interplant companion plants with the tomatoes.

I hope these raised bed questions are helpful! One tip, don’t overthink it! There is no rule saying once you put a raised bed in it has to stay that way forever. If you start something and it doesn’t work make a note of it and try it differently next year!