Yard-Challenged? Garden Help for Small Lots
As part of my Master Gardener volunteer activities, I teach classes at the Mesa Public Library. Over the winter, I have a substantial increase in the number of winter visitors who attend the classes. Unfortunately, when it comes to gardening, many of these folks have challenges, including limited space, lack of sunlight and restrictive HOA rules. These gardeners would like to grow, but are concerned about whether they can grow with limited space and sunlight. Others I have spoken to are renters and not allowed to create in-ground gardens. Therefore, I have assembled the following guidelines for these challenging situations.
First, assess your location. On a sunny winter day (December/January) evaluate your outdoor space several times throughout the day. Evaluate what parts of the yard or lot are receiving sunlight and for how long. Your plants need 6-8 hours of sunlight per day to thrive. Obtaining good light is more difficult in the winter for two reasons. From sunrise to sunset on the Winter Solstice in Phoenix, we receive less than 10 hours of light. The sun is also much lower in the sky, such that trees, other homes, and/or walls may be shading portions of the lot. (Ref. 1)
What if the area you wish to use as a garden doesn't receive the necessary 6-8 hours of sunlight? There are several options. Use containers on wheeled bases so they can be moved with the sun. Another option is to select plant varieties that tolerate more shade. Good winter shade-tolerant vegetables include lettuce, spinach, chard, arugula, broccoli, and related plants, kale, and radicchio. While growth may not be robust, these edibles can produce well with less sunlight than other vegetables. Beets, turnips, and carrots tolerate partial shade. Flowering and fruiting plants, such as tomatoes and peppers, require significantly more sunlight. For sunlight requirement of common vegetables, see UA Extension Publication AZ1713: Container Gardening In The Southwest Desert.
Bill Robinson's Container Vegetable Garden
Reflected light is nearly as beneficial as direct sunlight. If your lot receives reflected sunlight from a light-colored or reflective surface, your plants will benefit.
If you plan to garden all year long in Arizona, you will need to assess sunlight in the summer as well. Since the pattern of light changes, evaluate throughout a summer day. There are some differing considerations for summer light. Many plants won’t tolerate afternoon sun, and planting containers will heat up quickly in these conditions. Look for areas that have morning and noon sunshine and afternoon shade. If the home structures are close together, heat may build up between them. You will likely need to use shade cloth to keep both the foliage and the container from overheating. Be cautious of heat sinks, such as block walls, pavement, and buildings, which may radiate afternoon heat onto your plants.
Small Raised Beds
Small raised beds can be achieved with any scrap clean lumber, including pallet wood. Avoid using treated wood or wood that is contaminated with paint, oil, and the like. If you don’t intend to line the base of your raised bed, loosen the earth before adding garden soil so the plant roots can extend as deep as they need. We need to allow most vegetables a minimum of 12 inches of soil; root vegetables should be provided 16 inches. When starting, add soil about the level listed above, as it will settle when watered.
These blocks, available from hardware stores, allow inserting lumber to create easy raised beds. Pound a rod or piece of rebar through the hole in the center to hold the block in place
Over time, add compost and topsoil as the soil level drops. In raised beds, it is not necessary to fill with purchased topsoil. Our native clayey soils are sufficient for a good portion of the material you add to the bed. Clay soil holds water well and contains many minerals. What native clay soils lack is organic material. Therefore, mix in compost up to 35%. Over time, continue to add compost, as it breaks down and is used by the plants and soil. Sandy soil is not a good choice for a raised bed, as it drains too quickly, requires more frequent watering, and does not contain near the number of minerals in clay.
Given your situation, you may need to garden in containers. There are several critical differences between container gardening and in-ground gardening. The most important consideration is that the soil in containers will heat up and cool down much more than the earth. Therefore, your plants and their containers need protection from heat and cold. In the winter, water the plants and then cover them with a cloth-based material before any expected frost. Ensure the cloth goes all the way to the ground, to hold in warmth and prevent frost infiltration. In summer, both the foliage and the container need to be shaded from the afternoon sun, and heat-sensitive plants can benefit from a permanent shade cloth of approximately 50% shade during all daylight hours.
The second way in which container growing differs from growing plants in the ground is the action of the soil. Field soils drain by capillary action, which pulls excess moisture downward. Soils in containers have poorer drainage characteristics due to the shallow depth and reduced capillary pull; therefore, use a porous planting mixture and plenty of drainage holes. Keep in mind that there is a delicate balance between under-watering and over-watering in container gardening. (Ref. 3)
Carefully select the type of containers used for the garden. Typical nursery black plastic pots absorb heat. They are also thin-walled and will transfer heat and cold quickly. If you must use these pots, paint them a light color to reflect the sun. Another option is to use a pot-in-a-pot, with a layer of insulation between the containers. Insulation can be made from straw, leaves or soil. This is useful in both winter and summer to insulate soil and roots from temperature extremes. Add mulch to the top of the soil to protect against heat/cold, direct sun, and rapid evaporation. Choose the largest pot you can obtain, as the more dirt in the container, the longer it takes to heat and chill. Consider the size of the root system on the mature plant. Food grade 55-gallon drums cut in half results in large containers. The barrels and be purchased for around $25, making the resulting half-barrels $12.50 each. They are sturdy, last a long time and can be obtained in white. However, consider that these can become very heavy when filled with a foot or more of soil, so a furniture dolly or other wheeled arrangement permanently underneath is useful if you may need to move them.
Laura's half-barrel garden. Barrels are up on blocks for less bending. Wire is on top of barrels to keep out cats, dogs and goat. There is no wire over the arugula because none of the animals except the humans like it.
Don't forget, if you make your pot, drilling drain holes is very important. Your container should also be able to hold at least 12 inches of soil for vegetable planting, to allow the roots to go as deep as they would in the earth. Root vegetable need at least 16". Shrubs and trees will need much deeper pots. However, the bottom line is to use the largest containers you can obtain to minimize soil temperature variation.
Compost contains small amounts of Nitrogen, Potassium, and Phosphorus (NPK) as well as micronutrients, and provides these nutrients in slow-release form. The primary purpose of compost in the garden is to build soil by increasing the beneficial microbes needed to jump-start healthy soil. However, compost is not a complete fertilizer. Depending on the ingredients used to make the compost, the NPK will vary, but typically is not higher than 4-3-2, and may be as low as 1-1-1..
Container plants need more fertilizer than plants grown in the earth. Look for a fertilizer that contains micronutrients as well as the standard NPK. Many container potting mixes will contain fertilizer, but fertilizer will need to be added regularly. Fertilizers also include salts, and as we fertilize our container plants, the salt content of the medium increases. Excess salt is toxic to plants, just as it is to humans. The most apparent symptom of "salt burn" is browning and death of the tip or edges of the leaves that is bordered by a yellow "halo." To leach the accumulated salts from the containers, periodic applications of large amounts of water are necessary to flush out salts. Be sure that the excess water during these leaching events drains quickly and easily away. Softened water should not be used to water plants because of the high salt content. (Ref. 3)
You do not need to fertilize container plants the first two to three weeks after planting if you used a potting mixture amended with fertilizer. If you use native soil amended with compost, fertilize after planting. Nutritional levels usually drop after two to three weeks because plants use them and because nutrients are also leached from the soil with frequent watering. (Ref. 3)
The frequency of fertilization depends on the method you use. For example, if you use a liquid or soluble fertilizer, make an application every two to three weeks during the growing season. If more rapid growth is desired, fertilize every one to two weeks. Mix soluble fertilizer according to the label directions and apply as a normal watering. Apply enough of the solution so some drains out of the bottom of the container. If you use a dry, garden type fertilizer, apply it every three to four weeks. A one-half teaspoonful of fertilizer per gallon of soil mixture spread evenly on the soil surface is adequate. Watering after applying the fertilizer dissolves the nutrients and carries them into the root zone. Watering-in the fertilizer reduces chances of fertilizer damage to stems and roots. (Ref. 3)