Question #1

ImageMyprettyflowers asks: In Dave's Garden plant descriptions, sometimes three different pH's are listed as well as multiple zones. Is there any connection between the two? For instance, when multiple pH and zones are mentioned, is a lower pH better in a lower numbered zone and a highter pH better in the higher numbered zone? Or, does it just mean that the plant will do equally good in any of the pH's listed in any of the zones listed? I just want to get the optimal pH for each plant in my zone (9b).

Melody answers: This is an excellent question! The various zones and PH listings in PlantFiles give you a range where the plant can successfully grow. Most often, the middle numbers are the optimum growing zone or PH. The ultimate height and spacing numbers are also a range of what a gardener can expect. Generally, there isn't a connection between the zone and the PH number as you described, but climate and PH will have an effect on the ultimate height and spread. The healthiest and largest plants will be found in the optimum ‘middle conditions' of climate and PH.

Question #2

ImageWetlandgardener asks: I want to fill sinkholes with compost to enrich the soil. I filled them with leaves, now what? Do I buy soil and mix in with the leaves and add vegetable scraps from the kitchen? Do I buy sand, straw, or potting mix? Such fillings could be expensive. I'd like to fill the holes ASAP, and plant trees in them. The sinkholes often fill with water because the back yard is a wetland.

Melody answers: By adding leaves and kitchen scraps to the holes, they will eventually fill with compost. However, it will take several seasons without some additional material. Since you'll be planting trees, the rootball will take up quite a bit of space. This will help keep from having to use so much additional soil. Depending on the size of your sinkholes, you might not need much, and you could check with some farms or stables to get some of their manure to help fill in. Old manure and composted leaves make a great planting medium and many places will be grateful for you to haul it away. Potting mix is expensive and if you need to supplement with bagged material, you can actually buy garden soil or humus cheaper. Just remember that most trees do best when planted at the same level that they are growing, so make sure your holes are filled enough to raise the tree to that level. If the area is a wetland, I'd make sure that the trees I chose are ones that like wet conditions such as cypress, willows or sycamore.

Question #3

Image1googalous asks: I am new to the gardening world and have decided to plant a perennial plant garden. The coneflowers label states that I am to plant them 28 inches apart. My husband says that I am to double the inches to 56 inches apart. I am so confused. Can someone answer my question? When it comes to plants, trees etc. how much space am I supposed to give my plants?????

carrielamont answers: I agree, it IS confusing! It really depends on how long you want to wait and how much you want to do about the bare spots. (When my house was landscaped 50 years ago, the owners-builders didn't want to wait at all so everything is too close together and too close to the foundation.) Anyway...because coneflowers (Echinacea spp.) have a long taproot they might object to being moved once established. (Some people move their plants frequently.) Even planting them 28" apart, it should be a long time before they get too close together. Unless you're planting something else in between, 28" is going to look pretty sparse and need to be mulched heavily to keep down weeds. At 56" apart you would almost have to plant something else in the middle; look for other drought-tolerant plants because you're not going to be watering your coneflowers much, once they get established. Dave's Garden Plant Files suggest a maximum of 18" for spacing Echinacea. Maybe consider some bulbs (Lily of the Nile or species tulips with interesting foliage) or one of the many lovely Salvias. These should grow around or through the Coneflower if they get close. These are just suggestions I'm throwing out off the top of my head; feel free to do some exploring and come up with your own ideas. Here's a tip, though:coneflowers were developed from wildflowers growing on prairies where they got little water. To find companion plants, look for ones that are "drought-tolerant" or "suitable for xeriscaping". And welcome to the wild and wonderful world of perennial gardening!

sallyg adds: Plant spacing
28 inches apart means place one plant, then measure 28 inches from its center to place the center of the next plant. You'll end up with a little less than 28 inches of bare ground in between them. This is sometimes called "planting on 28 inch centers," ( or whatever the measurement may be.) Planting 28 inches apart will certainly assure ample growing room for those plants. One last tip: Try not to gloat when you tell hubby you are right. You may need him for heavy lifting at some point!

Question #4

sweet potatoJoelcoqui asks: I rooted very easily the green sweet potato vine. Can this be planted to stay indoor over the winter and brought outside in the spring?

Melody answers: Yes indeed! The ornamental sweet potatoes do fine as a houseplant. I like to take several cuttings and just keep them in water. They seem quite happy and I've had better luck with this method, rather than potting them up in soil. They grow, produce roots and seem quite happy. Every week or so, I change the water to keep it fresh. Sweet potatoes from the grocery store make a great houseplant too. I've stuck one end in water and the top part sprouts and produces a lovely vine. If the vines get too lanky, trim the tops and start again. Critterologist wrote a wonderful article about ornamental sweet potatoes that is quite informative and you can read it here.

Question #5

ImageCheviothunter asks: I have 3 flourishing citrus trees in containers that will need to come in when the temperature drops further. I have no sunny windows. What kind of lamp should I buy? The trees are about 2.5 feet tall. Would like to buy something attractive. Thanks for your help.

sallyg answers: I'm afraid you may have to compromise somewhere between attractive and functional. First, you will have to use fluorescent light. Incandescents will be too hot. Next you will have to direct the light onto the leaves as much as possible. Plants that flourish under indoor lights have a very bright situation. For example, I now have some small plants under fluorescent tube light fixtures. The plant leaves are all within eight inches of the surface of the bulbs. Any placement with natural light will give the trees some help, and in fact sunlight through a glass window can be too hot anyway.
This page from recommends 15 to 20 watts of fluoresecent lighting per square foot of growing area, for plants needing medium to high light . I would think citrus wants at least medium light. Place the lights within several inches of the plants. This might at least give you an idea. Good luck on finding fixtures that can provide those watts and fit your decor needs. By the way, leave the lights on for 12 hours a day if there is some natural or other light, up to sixteen hours a day if there is no other light source.

Remember, if you have a gardening question that you would like to suggest for this feature, post it here. Our writers and admins will handpick a few of your questions and answer them in an upcoming Ask-a-Gardener, one of our Saturday morning features. Other questions may be moved to one of our other forums so your fellow members can help you.