Raised Bed Gardens

I live in Queen Creek, AZ (Low Desert), ZONE 9a. That translates as hot, arid summers reaching 110-115 degrees, and winters with a low number of freeze days. It has its challenges because the mild winter is followed by harsh summers. However, the mild winters also provide an opportunity to have two growing seasons. Greens and root vegetables are wonderful during our cool season, which lasts from September through mid-January. Our warm-season planting from mid-February through mid-July includes fruits, beans, corn, some squashes and of course tomatoes. May & June offer the least precipitation then we get a deluge, called a monsoon, in mid-July through August. It’s feast or famine in the desert.

A few friends who want to garden asked me how to get started. My advice to new gardeners and advanced gardeners alike is to create raised gardens. They are the easiest way to get started in gardening and in places that have poor soil, they are the best choice for high yield, quality food.

As you can see from the photos below, two tomato plants that have the same height estimate on the seed packets had different results as to where they were planted. The raised garden bed produced a plant that grew to 47 inches and has produced 17 tomatoes so far. The second plant was planted into the ground in soil that was previously used for grass. I mixed 40 percent compost in with 60 percent of the native soil and fed it with the same natural fertilizer (fish emulsion) as I did with the raised bed. It only grew to 31 inches and it is just getting started with production.

Raised bed tomato plant
This tomato plant is currently 47-inches tall. It was grown in a raised garden bed.
Tomato plant in native soil
This tomato plant is growing in native soil with a mix of 40 percent compost and 60 percent native soil. It received the same fertilizer treatment as the tomato plant in the raised garden. It is only 31 inches tall currently. Both transplants were planted on the same day.

RAISED BED PROS
• Weeding is minimal. You are using a quality mix of soil that is weed free from the start. Since your bed is raised, many of the seeds that blow through the wind close to the ground won’t reach your raised bed soil either.
• It’s easier to control pests. Stressed plants draw bad bugs due to inconsistent watering or nutrient-starved soil. If you use quality soil and water consistently, much of your pest problems will be taken care of. I have a major problem with gophers in my area of the Valley. If I didn’t have raised beds, I would be at their mercy. When I built my beds, I laid down hardware cloth (much like chicken wire but much sturdier) at the bottom of each bed and rolled it up the insides a couple of inches so the gophers can’t enter on the edges. Some of you may have moles instead. We also have those cute little bunny rabbits – at least they are cute until they decimate your garden. With a raised bed, I can easily attach rabbit fencing to the PVC low tunnels I create on each bed (PVC arches over each bed that allow me to attach shade screens, winter blankets, bird netting, clear plastic for a greenhouse effect and rabbit fencing easily). They don’t like to hop up on the sides of the beds much, but the more daring ones are stopped by the fence.
• You can relax as your neighbors rototill or spade their gardens. All I have to do is put a new layer of compost on top of the soil after each season and give it a good watering of fish emulsion. I am good to go for the next rotation.
You will have immediate quality soil; you won’t have to deal with our alkaline, clay soil in Arizona or problematic soil in other regions. The correct mix of raised bed soil is below under Rules for Success.
• Your plants will receive better drainage, which will prevent soggy plant roots. Yellowing leaves can come from either under-watering or over-watering. It is hard to tell. Basically, it is a sign of stressed plants. Raised gardens allow better drainage so you avoid water-logged plants.
You will get a higher yield from your crops because the soil is such high quality. This also means that you can plant closer together, although make sure that you don’t let one plant shade another. It will stunt the growth of the shaded plant. The plants you have will also produce more fruit.
• You can lengthen your growing season(s) by using the low tunnels. Use shade cloths in the summer if you are in an area of high heat and use winter blankets to lengthen the production prior to frost. You can use low tunnels in a ground-level garden also. It’s just more difficult to manage.
• You can build raised gardens directly onto your grass, compacted soil, cement slab or pavers. I just want to caution you that if you create a raised garden on a cement slab, wood or pavers, you will lock out worms, which are so beneficial to your garden. If you are planting on grass, lay down a layer of cardboard at the bottom of your raised bed before you add soil. It will act as a grass/weed barrier and worms love to eat the cardboard.

CONS
• The Initial cost of construction & soil can be a deterrent for some gardeners. You can recycle products but don’t use any chemically treated woods like most palettes, railroad ties, or tires, which also release chemicals into your soil and vegetables.
• The soil may dry out faster because the walls can heat up the soil faster. You can correct this problem by using a water barrier and mulch. Or you can seal your wood safely
• Your space is more controlled since in order to add to your garden, you will have to build more raised beds.

RULES FOR SUCCESS
Mix the following ingredients in the following order for quality raised bed soil:
1. 2-3” native soil for natural water response for area
2. 6-8” Good quality organic- certified raised bed soil (not potting soil)
3. 1” Coconut Coir (retains moisture & nutrients) layer
4. 1” Earthworm castings
5. 1” Azamite (rock dust) minerals missing from our soil
6. Repeat Steps 2-5 until you reach the height you want
7. Fertilize with fish emulsion before planting

If this sounds too complicated, just use about 75% raised bed soil and 25% compost. You will still do fine to start and then build from there the next season with the added nutrients. The above mix is the best start, but I understand that new gardeners just want a simple plan.

• Grow what you will eat and buy plants locally and pay attention to what grows here
• Purchase seeds according to your zone and appropriate growing season
• Install an automated watering system when possible. It can be a professional installation or as simple as a timer on a garden hose. Next week, I’ll write about alternative ways of watering.
• Mulch and fertilize (spray foliage every other week: fish emulsion/compost tea)

Use your local planting calendar.

I have attached my Maricopa_Veg_Calendar, but also watch your frost dates – you want ground temperature at about 60 degrees to plant warm season vegetables. Cool season is dependent upon date, heat and precipitation.

NEXT WEEK: Raised garden structures and watering systems

Jknapp

I am a certified agriscape designer and Maricopa County Master Gardener. I have been gardening since I was six years old and worked in my grandfather's garden. I believe that the only way to be a responsible gardener is to garden organically. It improves our soil, is safer for us to eat, sustainable and it protects our pollinators and soil from chemical poisoning.