Raised beds are freestanding garden beds built above natural terrain. Gardeners in Texas have found that raised bed gardens can help with many problems. In many parts of the state, the soil contains too much sand or clay, or is too alkaline for some plants to grow well. Poorly aerated soil due to compaction or poor drainage can also be a problem. Soil quality issues are often more severe in urban and suburban environments, where topsoil and vegetation have been removed or grades changed during construction.
Raised bed gardens improve growing conditions for plants by raising their roots above poor soil. The soil in the bed can be modified to provide a better growing medium for plants, even those that won't naturally thrive there. Raised bed soils warm earlier in the spring and are less prone to intrusion by certain grasses and tree roots. Also, the height of loft beds may make them easier to maintain.
The first step in planning a loft bed is to decide on its location. Site selection and plant selection go hand in hand. Many vegetables, ornamentals, and herbs require lots of sun; beds for these plants should be located where they will receive full sun. If that's not possible, choose a location that receives morning rather than afternoon sunlight. If only shade is available, try growing shade-tolerant cool-season vegetables like broccoli, cabbage, and lettuce. Also, some ornamental plants do best in partial shade. In windy areas, place beds and protect them from prevailing winds by fencing, buildings, or other structures. Hospital beds should not be located in frost pockets or in areas with poor airflow, as fungal diseases usually develop in places with little airflow.
Raised beds should be well-drained, as maintaining very moist soil can deprive plant roots of oxygen. Also, plant diseases are more likely to develop in wet conditions. Good drainage is especially important in vegetable jars. Soil and location determine the drainage capacity of raised beds. If the bed contains clay, amend it with at least one-third of the volume of grit, organics, or coarse-grade perlite to improve drainage.
Don't find a bed in the swamp, it will sit in the water. Build landscape beds so they slope about 2% (1/4 inch drop per foot of horizontal distance) away from any structure, or away from the center of the bed. Sometimes special drains need to be installed; determine this during the planning stage. Drain tiles or septic pipes extend the length of the bed and create drainage channels through the walls at both ends. Usually, a row every 4 to 6 feet is sufficient. Another method is to dig a trench in the desired direction of water flow (from the bed to lower elevations), lay 3 to 4 inches of rough stone in the trench, and then lay a tile made of clay, concrete, or plastic in the center of the trench or perforated tubes. Cover the trench with rougher stones, then soil. A French drain is another option, just a narrow ditch filled with rough stones leading from a poorly drained area to a lower elevation.
A loft bed should blend in with its surroundings. The bed design can be formal or informal, depending on its shape and the type of edge chosen. A rectangular bed with a low brick wall at the edge, filled with yaupon (Ilexvomitoria) or boxwood (Buxusspp), trimmed to a straight hedge or topography, has a formal look that might fit at the front of the house. The irregularly shaped perennial border hidden behind a dry stone wall is less formal but attractive almost anywhere in the landscape. Vegetable gardens have an informal look and are best suited for private areas of the yard. The size of the bed should be in proportion to the surrounding space.
A loft bed doesn't have to be very deep to be effective. 8 to 12 inches is usually sufficient. If drainage is an issue, or if you are growing plants that prefer dry soil, the bed can be taller and filled with porous growing medium. Vegetable beds should be 12 to 18 inches deep. The material used for the edge of the raised bed should be stable, durable and attractive. It is the edges that give the bed its "look" in the landscape. It also establishes the contours of the bed and holds the soil in place. Edges can be as simple as metal tape, rail ties, or landscape wood, or as complex as mortar brick or stone. A top bed is a bed in which soil is simply piled up from the edge of the bed to the center; it may or may not have an edge.
Metal edging is available in lengths of 8 to 10 feet, is easy to install, and is convenient for bending the edge of the bed. However, it will rust over time and may not be as appealing as you would like unless the plant overflows the bed or the edges are camouflaged with a more aesthetically pleasing material. Cable ties and wood can be laid individually or in layers and have a rustic look. Rail ties treated with creosote don't seem to cause any health problems, as most of the creosote has leached out. There is some controversy about the use of treated landscape wood, but research shows that any leached compounds are well within safe levels determined by the EPA, whether in growing media or in harvested produce. If you're concerned about using treated wood, line the inside of the bed walls with polyethylene, roofing felt, or a similar material to create a protective barrier. Stone walls make interesting beds, and cracks and openings can be built for creative planting.
However, stones can be expensive. Interlocking pavers are growing in popularity and are easier to install than mortar stones. No matter which edge material you choose, it should be strong enough to hold the growing medium and withstand being hit or ridden by a riding lawn mower. It should install properly and complement the rest of the landscape.
The design phase is the perfect time to decide how to irrigate your raised bed. Hand watering may be easiest in many cases, but it can get tedious; gardeners must also know when to water and how much watering or how much pain the plant will suffer.
Regular watering of beds is effortless with a sprinkler system, but this method wets the leaves, which can lead to disease and salt damage. If the system automatically timed it, it could appear regardless of recent rain, wasting water. So, an automated system may be the most convenient for the gardener, but it's not necessarily the best for the plants. Pop-up or fixed risers are prone to evaporation and drift in windy conditions. Low-flow systems can be more efficient in warm, windy conditions.
Low-flow irrigation systems for woody plants and vegetables include micro sprinkler, drip, drip and soaker hose systems. These systems conserve water, can be installed under mulch, can regulate flow at the rate desired by individual plants, and are less likely to wet the leaves. However, they do have some drawbacks. Unless the water used is very clean, the transmitter tends to clog, and if the transmitter is installed under a cover, it can be difficult to spot a problem. Dischargers are also sensitive to elevation changes along irrigation lines, requiring pressure compensation lines. Finally, rodents and other wildlife can easily damage some drip lines.
If you choose a sprinkler system, determine how many sprinklers you need, and whether the sprinklers will pop up or be set on risers. Be sure to consider spray overlap, spray angle and spray head height. Always design the system so that at least one additional riser card can be added to each section in the future. You may need this flexibility as your planting matures. If you choose drip or drip irrigation, determine the length of the hose and the number of emitters needed. Drip tapes with 12" emitter spacing are best for vegetables.
The beds should be divided according to plant needs, system size, available water pressure, and available water flow. Area watering can be manual or timed. There is no one irrigation system suitable for all raised beds. Sometimes a combination of systems works best.
Build a Raised Bed Garden
Set the perimeter layout
If the bed has straight lines, use stakes and string to outline the perimeter. Garden hoses or ropes are great for framing curved beds. Most vegetable beds are square or rectangular so vegetables can be grown in rows. Many decorative beds are curved. To make maintenance, especially trimming, easier, design the bed with long, flowing curves instead of many tight curves.
remove existing vegetation
Remove any woody plants with a wood, handsaw, or chainsaw, then dig out the roots. Use systemic herbicides to kill perennial weeds and keep them from returning. Alternatively, cover the bed area with clear plastic (anchor the edges with rocks or soil) for 1 to 2 months to kill vegetation without herbicides. If temperatures warm both day and night, the heat generated under the plastic will kill the plants, albeit not as quickly as herbicides. Once the site is clear of vegetation, you must till the soil thoroughly.
Metal. The metal edges are usually 4 to 6 inch wide metal strips of varying lengths. They are connected by wooden stakes inserted through overlapping notches. Lay the strips along the perimeter edge of the bed, overlapping the ends, lining up the notches. Hammer the stake into the soil through the overlapping gap. Using a rubber mallet or hammer and a piece of wood on top of the edge, gently hammer the edge into the soil between the stakes. It is best to partially sink the stakes until all the stakes are in place, then sink it to the desired depth. If the soil is hard and dry, soften it with water, or dig the soil to accommodate the edges.
Bricks/Cinder Blocks. To build a brick-edged raised bed, start by pouring concrete footers that are at least 6 to 12 inches high and 16 to 18 inches wide. This will be the bottom of the wall. Dig the footer ditches carefully so you don't need to use a form. After pouring the concrete, insert a 3⁄8-inch rebar rod into the center for stability (especially important in clay). Smooth the top of the footer with a spatula. After the footer has cured for 3 or 4 days, wet it and apply about 3⁄4 to 1 inch of mortar about 2 feet below the slab. Press the first brick into the mortar, leaving about 1⁄2 inch of mortar between the brick and the plate. Apply mortar to the side of the next brick and place it 3⁄8 inches from the first brick. Use the handle of a spatula to lightly crush the bricks to secure them and remove excess mortar squeezed from between the bricks. Continue until the edge is complete. Cinder block edges may not need mortar because the blocks are larger.
Stone. To elevate the stones, roll them up a plank over a pipe or use a hydraulic lift. To install dry stone wall, first level the surrounding terrain. Place stones in each row so that they overlap the stones below. Make the bottom wall wider than the top one, and don't push the stone inward for stability. If the wall is multiple stones thick, periodically insert tie stones/long stones across the width of the wall. This makes the wall stronger. If the wall is more than 2 feet high, it should be mortared in place and built into concrete footers. One test fits two to three stones before applying the mortar. To ensure good contact between the mortar and the stones, lay the first layer of stones while the footer is still wet, and use the handle of a spatula to crush the stones sharply to secure them. If the stones are heavy, insert dowels between the stones to prevent the mortar from being squeezed out before it dries. After the mortar has partially set, remove the dowels and fill the holes with mortar. You may need expert help, as poorly constructed stone walls can be dangerous. Also check local codes to determine if the plan requires an architect's stamp.
Landscape wood. Level the perimeter of the bed, level the first layer of wood or set it on the desired slope. Run rebar or galvanized spikes through the end of the wood at a 20-degree angle into the soil about 12 to 18 inches at a 20-degree angle. Overlap successive layers of wood and nail them to the previous layer with galvanized spikes. Check the level or desired slope frequently during construction.
Install the irrigation system
If you have gutters or sprinkler systems, install them before adding soil to the bed.
To help keep lawn grass away from the bed, especially Bermuda grass (Cydonondactylon), you should install a weed barrier between the edge and the soil. Then you can add soil or growing medium.
The soil should retain enough moisture so that the roots of the plants do not dry out, but it should also have good drainage. Soil with too much sand doesn't hold moisture well; soil with too much clay doesn't drain well. In general, sandy clay loam soils are best for most plants. It should be mixed with organic matter such as sphagnum moss, composted manure, sawdust or turf. Cacti and succulent beds may require highly aerated materials, such as crushed granite, with little or no water.
Soil is sold and delivered by cubic yards and can be ordered as a topsoil/compost mix. Common mixtures are three-quarters topsoil and one-quarter compost, three-quarters topsoil and one-third compost, or half topsoil and half compost. The higher the organic matter content, the sooner you will need to add more soil/compost to the bed as the organic matter will break down over time. Make sure the organic material is composted before adding it to the soil. Otherwise, it will deprive the plant of nitrogen as it decomposes. The best medium for vegetables consists of one-third topsoil, one-third peat moss, and one-third sand or coarse perlite. Standard potting soil or commercial container mixes are also good for growing vegetables, but are often too expensive to fill large beds. When filling the bed, grade the soil so that it slopes slightly from the center of the bed to the edges and away from adjacent structures.
Incorporating existing trees or shrubs into raised beds can be difficult. The easiest way to do this is to surround the plant with a metal edging to keep soil and excess mulch away from the plant's crown. Leave as wide a space as possible between the edge and the plant. Tree wells can be used for higher beds. However, it's important to remember that adding a lot of soil to the roots of established plants can kill them.
Planting and Covering Raised Bed Gardens
Make sure that the plants you choose are suitable for your area's climate and water, and that they are a mature size suitable for their location in the landscape. Perennials and permanent trees and shrubs should be located in the back of the bed where they are least disturbed. Plant annuals along the edges so they'll be easy to reach when it's time to replace them.
Mulch is probably the most important finishing touch to your raised bed garden. Mulch keeps plant roots cool in the summer, reduces evaporation of water from the soil, controls erosion by softening the effects of rain and slowing runoff so it can soak into the soil, and suppresses weeds. The mulch also adds to the attractiveness of the landscape.
After all the plants are in the bed, apply a 2 to 3-inch layer of mulch, tapering it to the base of the plants. To determine how much mulch you need, multiply the length of the bed by the width and depth of the mulch you need. Divide this total by 12 and then again by 27 to get the amount of mulch in cubic yards.
Both bark and pine needles are popular mulches. Many vegetable gardeners use shredded newspaper or strips of black plastic held in rows. Seeds or seedlings are planted in holes cut in the plastic. Newspapers and exposed plastic are not particularly attractive and should be kept in private areas of the garden.
Maintaining a Raised Bed Garden
Maintaining a raised bed garden involves weeding, irrigation, trimming and replacing decomposed mulch, as well as removing spent plants. Here are some guidelines for keeping your garden in top shape.
Water the bed as needed, allowing the top inch of soil to dry out between waterings. If plant species are complementary, their water needs will be similar.
Leave 2 to 3 inches of covering on the bed. The mulch should be suitable for the area and may be pine straw or wood chips in East Texas, and stone or gravel in West Texas.
Add compost or organic mulch twice a year in spring and fall. This replenishes the soil and acts as a slow-release fertilizer. Just rake the mulch back, add compost, and replace the mulch or add new mulch over the old. Alternatively, add inorganic slow-release fertilizers before and during active plant growth.
Trim each plant properly according to its purpose and intended design.
Control pests and diseases. You can reduce the need for chemical treatments by implementing integrated pest management: start with high-quality plants; handle plants carefully before and during planting; choose plants that are appropriate for your area.
Well-designed, constructed and maintained loft beds will be a source of lasting beauty in your landscape.