What to do with a new flowerbed

Q: The only place in my yard that gets full sun is the garage. Half of it was converted into a guest room. I want to build up the area in front of the guest room with stones for plants. It would be about 10 feet long by 4 feet high and 4 feet wide. Since the bottom will be concrete from the driveway, shall I treat it as a big planter with drainage and new soil every year, or can I just plant perennials and treat it like the rest of the garden?

A: You can treat this flowerbed either way, but it is probably much more economical to leave the soil in it each year. If you build a retaining wall completely around the 10-by-4-foot area and it is 4 feet high, it would hold 160 cubic feet of soil, which is around 5 cubic yards.

First, lets discuss the stone wall. If you need to build a wall that tall for some reason, go ahead and do it, but it won’t be necessary for most plants. An 18-inch-to 2-foot tall wall will supply all plants from medium size shrubs on down to annuals with plenty of soil. This height range is also a natural size for use as a sitting wall. Roots need air in the soil and there won’t be enough air in the soil 4 feet down for roots to grow well. If the planter must be that tall, you could fill the bottom 2 feet with gravel. Use a weed barrier cloth between the soil and gravel to prevent the soil from eroding and plugging the gravel with dirt.

You can build a three-sided planter if the fourth wall will be the foundation of the structure. Never allow the soil to be higher than the top of the foundation. Moist soil should not be against any siding.

If you are in a climate that freezes, you will want to line the inside of the planter with 1 inch or 2 inches of foam board insulation to protect the plant roots from cold and drying winds. You do not need to add a drainage pipe, layer of gravel or any coarse material at the bottom. Water will naturally reach the concrete and move downhill out from under the walls. Whichever direction the driveway slopes will get a layer of dirty or slippery water flowing over it. It could be stained from the material in the soil. Cutting some grooves in the concrete in a different direction may allow the water to flow where you want it to go.

Fill the planter with good top soil or a mix of soil and lightweight potting soil. If the driveway were raised like a parking garage, then the whole thing should be a lightweight mix. Leave the soil several inches below the top of the wall so that bark mulch can be added without it spilling over the wall. Even after the mulch is added, a little more room is needed so that rain can land on top without washing everything over the wall. The bottom 2 feet of a tall planter could be filled with Styrofoam beads to keep it lightweight. If you are going to grow desert plants or succulents, then the mix should be sandy, with some loam for water retention.

Any perennials, annuals, vegetables or small shrubs will do fine in a good soil with such good drainage. It is easy to maintain plants, especially vegetable gardens, in a raised bed. There is less bending over to do for weeding and harvesting. They can even be maintained while seated in a wheelchair. If the bed has access from all sides and is only 4 feet from front to back, the whole area can be reached. You must take into account the front to back thickness of the wall stones to keep the whole bed reachable. Also, some walls need to be wider at the base, so take that into account, too.

You can take out a stone or two in various places around the wall and use these spots as planting pockets. Many perennials spread as vines or ground covers and they can look very nice as they cascade down the wall. Strawberries can also be used.

It is even possible to install a small water garden pond in a raised planter. You can use a preformed plastic pond just by sitting it on the concrete and supporting the shelves with stones or bricks. A flexible rubber liner can be used by adding the soil first, then digging and shaping it. Or, by using stones or bags of sand to create the shelves the liner lies on. In either case, soil and plants can be added around the pond liner to finish the plantings. A two-tiered stone wall can be built so that a small waterfall can be built across the middle of the planter.

Q: I planted a gardenia and the next year, it only had a few flowers. In the following years, it has never bloomed. It is planted by itself, 2 feet away from a south white wall that gets a lot of sun. No matter how I have fertilized it, it hasn’t bloomed. What seems to be the problem?

A: Gardenias tend to prefer more shade than yours seems to be getting. They do like to be protected from winter winds and so the south side near the house may be good from that point of view. The flower buds can be less hardy than the plant, so maybe they are getting killed each winter. They should be noticeable on the plant for several weeks or months before they bloom, so you can see if they develop and fall off or just never develop.

They prefer acidic soil conditions and the fertilizer should have been labeled as being specifically for gardenias and maybe rhododendrons or azaleas. If not, try some of that. They do get several insect problems of aphids, spider mites and whiteflies, but any of them would make the whole plant sickly, besides the non-blooming.

Gardenias do not tolerate abrupt changes in air temperature or soil moisture. If they experience either condition, they will develop yellow leaves that fall off. If it happens several times in a row, they will drop flower buds too. They normally will drop leaves at about the time they normally bloom.

Maybe your plant is protected from the cold until it gets really cold. If it were farther from the building, it would have experienced cooler weather before the big drop in temperature. Being next to the warm south wall may also cause the soil to dry out too much.

E-mail questions to Jeff Rugg at info@greenerview.com.

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