Customers visit Merrifield Garden Center everyday with a host of gardening questions. We have a Plant Clinic at both of our stores, which is staffed by garden experts who can diagnose any plant problems that you may be having, and answer any gardening questions that you may have. If you are experiencing a plant problem, we recommend that you bring a fresh sample that is representative of the problem into the garden center, and we will diagnose it and discuss control recommendations with you.
For your convenience, we have listed below a sampling of some of the most common questions that we receive at the garden center, along with brief answers to each question. Simply click on the categories that you are most interested in learning about. If you need further information or need to discuss a particular issue, please visit our Plant Clinic at either Merrifield Garden Center location.
Pruning & Fertilizing
Q: When should you prune spring flowering shrubs and trees such as azaleas, rhododendrons and lilac?
A: Since these plants bloom on previous year's wood, they should be pruned after they bloom or else you will sacrifice flower buds. Pruning should be done within six weeks after blooming. This is also a good time to feed them. We recommend Merrifield Flowering Plant Food, a high phosphorous formula that will promote flowering.
Q: When should you prune summer flowering shrubs and trees such as spirea, butterfly bush and crape myrtle?
A: These plants should be pruned in the early spring before the new growth begins to emerge. Bigleaf, Oakleaf and Climbing Hydrangeas are an exception to this rule. They are late spring or summer flowering, but they bloom from the previous years growth. So, they should be pruned only if necessary and after flowering.
Q: When should you prune evergreens?
A: Most evergreen trees and shrubs should be pruned either in the early spring (for a natural appearance) or late spring after the new growth has flushed out (for a more formal appearance). This includes both needled evergreens such as yews, spruce and juniper and broad-leafed evergreens such as boxwood, hollies and laurels. One notable exception to this rule is the spring-flowering group of evergreens such as azaleas and rhododendrons, which should not be pruned until after they have bloomed or else you will sacrifice flowers. These plants should be pruned within six weeks after they bloom for that is when they will begin to set buds for next year's blooms.
Q: When should you prune shade trees?
A: We recommend pruning shade trees in late February / March. This is also a good time to feed them with a good quality, slow release fertilizer. We recommend Merrifield Tree and Shrub Food, which contains slow release nitrogen, sulfate of potash, iron and other micro-nutrients.
Q: When should you prune roses?
A: Major pruning on roses should be done in March. Cut the roses back to about _ their current height (usually about 18Ó – 30Ó). Other light pruning can be done at other times of the year as needed, such as during the fall to remove long branches that might break off during the cold windy winter.
Q: When should you cut back liriope and ornamental grasses?
A: Both of these plants should be pruned in March. It is important that these plants be cut back each year, because they put out new foliage from the ground to replace last year's growth, which will not rejuvenate itself. Liriope should be cut back to about 3Ó. How far you cut back ornamental grasses will depend on the age and size of the plant. A smaller grass that has only been in the ground for a few years should be cut back to about 4Ó- 5Ó, whereas a larger one that has been there for some time will need to be cut back to about 6Ó – 8Ó. When cutting back larger grasses, instead of cutting straight across the top of the plant, make your cut in the shape of a mound with the center a few inches above the sides. Cutting back large ornamental grasses straight across the top of the plant could lead to the middle of the plant dying out, meaning that it will not come back.
Q: When should you fertilize most trees and shrubs?
A: Most plants will benefit from a spring and fall application of fertilizer. We recommend using Merrifield's custom blended plant foods, which contain slow release nitrogen, sulfate of potash and micronutrients. Choose Merrifield Flowering Plant Food for flowering trees and shrubs and Merrifield Tree & Shrub Food for evergreens and shade trees.
Q: When should I fertilize my annuals and perennials?
A: Annuals will generally benefit from frequent applications of fertilizer throughout the entire growing season. Using Merrifield's Flowering Plant Food every 4-6 weeks will keep your annuals growing and blooming all season. Perennials do not require as much fertilizer as annuals. Fertilizing with Merrifield's Flowering Plant Food one time in early spring will promote strong blooming.
Planting & Watering
Q: Should organic matter and starter fertilizer be mixed into the soil when planting?
A: Yes, we recommend using Super Fine Soil Conditioner and Merrifield Starter Plant Food at the time of planting. Please see our proper planting and watering instructions on the link above.
Q: Should shrubs and trees be watered after they are planted?
A: Yes, all plants should be watered thoroughly after they are planted, and then as needed to keep them healthy. How often you water may vary depending on factors such as the size of the plant, where it is growing, and how much natural rainfall we receive. You will need to monitor your plants water requirements by checking the moisture level of smaller plants every 2-3 days and larger plants and trees every 3-4 days to determine how dry or wet it is to know when it is time to water again. Please see our proper watering instructions above.
Q: How often should plants and trees be watered?
A: The real answer depends on several factors such as how long the plant has been growing in the landscape, where it is growing in the landscape and how much natural rainfall we receive. Obviously a newly planted tree will need more water from you in a dry season than during a rainy season. The short answer is that all plants need to be watered as needed for the first year or so until natural rainfall can take care of most of their moisture needs. Check the moisture level of smaller plants every 2-3 days and larger plants and trees every 3-4 days. If they are moist, leave them alone and check again in another few days. If they are dry, water thoroughly. Once you have checked a few times, you will learn how long it takes your particular soil to dry slightly between waterings. Please see our proper watering instructions on the link above for more guidance on watering.
Q: How often should I water plants in containers?
A: Plants growing in containers have a limited about of soil and therefore a limited amount of moisture for the roots to tap into, and therefore, need to be watered more frequently than plants growing in the ground. Monitor your container plantings daily and water as needed. During the hot and dry summer months, you may need to water your container plantings every day. Using a water-grabbing polymer such as Soil Moist can help reduce the frequency of watering.
Q: Should trees be staked when they are planted?
A: Generally speaking, trees do not need to be staked when planted. However, if you are planting trees that are in an especially windy location, then they should be staked. It is important to know that if you do stake trees, the stakes should be removed one year after planting. Otherwise, it could weaken the trunk of the tree and the roots may not develop the ability to anchor themselves into the soil properly.
Mulching
Q: When should you mulch the garden?
A: Mulching should be done at least once per year. This can be done at anytime of the year, be it spring, summer, fall or winter. Many gardeners choose to mulch in the spring because that is when they are cleaning up the garden for the year ahead and when a lot of weeds are beginning to emerge.
Q: How deep should you apply the mulch?
A: Approximately 2Ó-3Ó of mulch should be applied to garden beds, but remember to taper the mulch back to ground level as you get near the trunk of the plant.
Q: When applying mulch, should you remove the old mulch first?
A: This depends on several factors such as how often you mulch, how much mulch you apply each time and the type of mulch. If you only applied a thin layer of mulch the last time and it has broken down quite a bit, then it is generally best to turn the mulch over, work it into the soil and then add new mulch right on top of the old mulch. That way, it will continue to breakdown and become beneficial organic matter. But if you have several inches of old mulch piled up from previous mulching, you should remove the old mulch before applying the new mulch.
Q: What is the best type of mulch to use in the Washington area?
A: All mulches help conserve moisture, retard weed growth and provide an attractive appearance in the landscape. Simply choose the mulch that you feel looks the best. Merrifield Garden Center's shredded mulch is our most popular seller, but any of our good quality mulches will do the trick. In some situations there may be practical considerations; for example, mulch chips or nuggets are not ideal for hillsides or slopes for they can spill out of the beds more easily.
Q: Does mulch have termites?
A: Merrifield Garden Center's mulch, and other mulches made from the bark of a tree as opposed to the tree itself, does not have termites. Termites must have proper temperature and humidity to survive and they have only one reproductive queen in each colony. If a reproductive queen were to survive the debarking, shredding, double shredding, transport and delivery, which is nearly impossible, she would starve upon arrival. Termites feed on cellulose, which is found in wood, not in the bark. Termites will swarm in the spring to form new colonies. People often-put down mulch in the spring and assume the termites came from the mulch.
Lawn Maintenance
Q: After applying a lawn weed killer, how long do I wait before mowing the lawn?
A: For best results, mow your lawn 2-3 days before applying any weed killer and then wait at least two days after application to mow your lawn. This allows time for the weed killer to be absorbed by the weeds.
Q: How often and when should you fertilize the lawn?
A: Cool season grasses such as bluegrass, fescue and ryegrass should be fed once in the spring and two or three times in the fall during the months of September, October, November and December. Warm season grasses such as zoysia, (which turns a tan color from October – April) should be fed one or two times per year from May-August. We recommend using Merrifield Premium and Merrifield Select Lawn Foods, which have been custom blended for the conditions in this area.
Q: Can you seed the lawn and kill weeds at the same time?
A: No, you must either kill weeds first and then wait 3-4 weeks to seed, or seed first and then wait until the new seed has germinated and been mowed at least twice (about six weeks) before applying a broadleaf weed killer.
Q: Can you lime, fertilize and seed at the same time?
A: Yes, you can apply all three to your lawn the same day and then water it in when you are finished. Just remember you cannot apply a weed killer to the lawn and seed the lawn at the same time. The next time you are in one of our garden centers, be sure to pick up our brochure, ÒGuide to Year Round Lawn Care,Ó which contains detailed instructions for building a healthy lawn.
Q: When can you seed the lawn?
A: Although seeding can done at virtually any time of year, the ideal times to seed the lawn is during the fall between September and October or in the spring during the months of March or April. These times typically provide cooler temperatures and more reliable moisture, which makes for ideal growing conditions. Dormant seeding can also be done in the late fall and winter, but the seed will not germinate until the spring.
Q: When can you lay sod?
A: While spring and fall are the ideal times to lay sod, sodding can also be done at almost any time of year, except when the ground is frozen. Sod can be laid in the summer months, but you will probably need to water more frequently. So again, March through November is typically when sod is laid, but it can be laid even later if the ground is not frozen and sod is available.
Q: When type of sod is available?
A: At Merrifield Garden Center, we carry three types of sod. For cool season turf (which stays green year round and is what most of us in this area have), we carry both tall fescue and Kentucky bluegrass sod. If you have full sun / part shade, both varieties will grow nicely. If you have areas that receive more shade, tall fescue is the best choice. We also carry zoysia sod, which is a warm season grass that turns tan in color from October – April.
Q: When is the time to prevent crabgrass in the lawn?
A: Technically speaking, for crabgrass to germinate, soil temperatures need to be 56 degrees for three straight mornings measured at 10 a.m. In our areas, that means that crabgrass preventers should be applied between mid March and early April. If possible, do this before a good soaking rain. Otherwise, be sure to apply a _Ó of water to the lawn.
Q: Can you seed and prevent crabgrass at the same time?
A: You can seed the lawn only if you use a product containing Tupersan to prevent crabgrass. Tupersan stops crabgrass from germinating while allowing the grass seed to germinate. To make sure you do the job right the first time, we invite you to come into the garden center and speak to one of our turf specialists.
Q: Why do I have moss growing in my lawn?
A: Could be one of several factors such as low pH, lack of fertility, compacted soil / poor drainage or too much shade. See one of Merrifield Garden Center's plant specialists for guidance.
Q: What is the best grass seed for my lawn?
A: Tall Fescue is the most popular turfgrass in the mid-Atlantic region. It is a very adaptable grass, which grows in full sun or part shade. It is also the most heat and drought tolerant of the cool season grasses. Merrifield Tuff Play is a Tall Fescue blend mixed with a small amount of Kentucky Bluegrass. This combination of grasses develops a dense, wear resistant lawn for sun or part shade.
Merrifield Shady Lawn Grass Seed is for use in heavy shade. It is a mix of Fine Fescue that is able to compete with trees for sun, water and nutrients. It is slow growing and takes longer to establish than Tall Fescue.
Merrifield Sunny Lawn Grass Seed is a Kentucky Bluegrass blend mixed with perennial ryegrass. This will develop into a dense, fine bladed, dark green lawn. It does require more water and fertilizer than tall fescue.
All of the Merrifield Lawn Grass Seed Blends contain top rated turfgrass varieties for this region. They have been under evaluation for at least three years at the University of Maryland and Virginia Tech and blended to our specifications.
Q: Should I fertilize at the same time as seeding?
A: Yes, we suggest fertilizing with Merrifield Select fertilizer whenever you are seeding, or sodding. Merrifield Select is a high phosphate, slow release fertilizer that will help the seedlings to establish, without burning.
Trouble Shooting
Q: Why are the leaves on my azaleas turning yellow in the fall?
A: If you have white blooming azaleas, it is totally normal for the leaves to turn a pale yellow color in the fall.
Q: Why are the leaves on my azaleas turning burgundy in the fall?
A: If you have red or pink blooming azaleas, it is totally normal for the leaves to turn a burgundy color in the fall.
Q: Why are my white pines, arborvitae and hinoki cypress dropping so many brown needles in the fall?
A: It is totally normal for evergreens to have their interior needles turn yellow and fall off around October. This is normal shedding for evergreens.
Q: Why are the leaves on my azaleas (or other broadleaf evergreens) turning yellow, while the veins inside the leaves are dark green?
A: This condition could be caused by an iron deficiency in the plant, often brought about as a result of the pH level of the soil being too high or too low for that plant. If this is the case, you can apply iron to the plant and then check the soil pH to see if it needs addressing. See our staff for guidance.
Wildlife Damage
Q: Deer are destroying my garden, any suggestions?
A: Deer browsing is difficult to prevent and a combination of control strategies will be necessary. Fencing is the most effective way to prevent deer browsing. The fence must be a minimum of 7' and the more visible it is to the deer, the better. Selecting plants that are considered deer resistant will help to make your garden less attractive to deer, and using repellents on a preventative basis can help. It may take some trial and error to find the most effective repellent for use in your garden. Alternate between repellents to prevent the deer from becoming accustomed to any one repellent.
Q: Plants are disappearing from my garden, what's up?
A: Check for voles. Voles are burrowing rodents that look like mice. They tunnel through the soil and feed on plant roots. Excessive mulch will encourage voles, reduce mulch to a one to two inch depth. Vole Block is a natural, permanent deterrent to voles. It is an aggregate material mixed into the soil at the time of planting. Traps and poisons can also be used to reduce vole populations.
Q: Moles are destroying my lawn, what can I do?
A: Moles tunnel through the soil in search of insects to feed on. In the big scheme of things, they are beneficial critters helping to control insects and aerating the soil. They can become a nuisance creating raised tunnels through the lawn leading to scalping of the turf and causing a potential tripping hazard.
Mole repellents are non-toxic, easy and effective. There are various formulations of castor oil, sprayed over the lawn and watered into the soil. Repeat application may be required. Traps and poisons are also available, but must be used with caution.
Q: Squirrels are digging in my planters. How can I stop them?
A: Dried Blood is an organic fertilizer and a reasonably effective squirrel and rabbit repellent. Dust your planter boxes with dried blood every 2-3 weeks until the squirrels lose interest in your planter boxes.
Cultural Practices
Q: How do you raise or lower the pH level of the soil?
A: Lime will raise soil pH, while garden sulfur or aluminum sulfate will lower the pH.
Q: My bulbs have finished blooming and the green foliage looks messy, can I cut them back now?
A: Since bulbs get energy from the nutrients produced in the leaves, you should wait until the foliage turns brown before cutting them back.
Q: How do I change the color of my blooms on my hydrangea from blue to pink?
A: To make the blossoms pink, you need to sweeten the soil or increase the pH level of the soil. This can be done by applying lime to the soil.
Q: How do I change the colors of my blooms on my hydrangea from pink to blue?
A: To make the blossoms blue, you need to lower the pH level of the soil. This can be done by applying pelletized sulfur to the soil.
Q: How can I get my wisteria to bloom since it has not bloomed for years?
A: This can be tricky. Although most wisteria purchased from a reputable nursery will flower, many native wisterias can be very stubborn about blooming. In fact, regardless of what you do, some native wisterias unfortunately may never bloom. Here are some steps that you can try, however to try and help them flower. First, fertilize with a high phosphorous plant food (no nitrogen). Second, prune them back heavy in June to stimulate growth. Third, you can try root pruning, by taking a shovel and making a series of cuts in the ground. Making a circle around the tree about several feet out from the main trunk, take a shovel and cut into the ground about every 12Ó. So if the circle were a clock with the tree in the middle, make cuts at 12, 2, 4, 6, 8 and 10. By cutting the roots, you are stimulating growth, which often will encourage flowering.
Insects
Q: What are the white cottony balls that are all over my hemlocks?
A: They are Hemlock Wooly Adelgids. This is an insect pest that sucks sap from the tree. The tree is gradually weakened and eventually killed by the insects. Spraying with horticultural oil, or drenching the roots with a systemic insecticide can control hemlock Wooly Adelgid. Bring a sample to our Plant Diagnostic Clinic and we will confirm the problem and make specific control recommendations for you to follow. Always follow label directions.
Q: What are the white specks all along the stem of my euonymus?
A: These white specs are euonymus scale. Scale are insects that suck sap from the plant resulting in poor growth, branch dieback and death of the plant. Scale insects can be difficult to control and proper timing of spray applications is critical. There are two generations each year of euonymus scale. The spring generation is treated in mid and late May. The summer generation is treated in early and mid August. There are various insecticides labeled for use on euonymus. See our staff for guidance and specific control recommendations.
Q: What are the bags of caterpillars that form in the crotch of branches on my cherry tree?
A: The Eastern Tent Caterpillar is one of our earliest insect pests, hatching in early April. The caterpillars eat the foliage of cherry and plum trees while building ugly, web-like nests. They can easily be controlled with Thuricide, a biological insecticide. Spray the foliage of the tree and the caterpillars will ingest the thuricide (always follow label directions). See our staff for guidance.
Q: What are the bags that look like Christmas tree ornaments hanging from my arborvitae?
A: These are bagworms, caterpillars that feed on a number of different needled evergreens. They can be controlled with Thuricide, but it must be applied when the caterpillars are young, around June or early July (always follow label directions). If you discover the bagworms later in the year, remove them by cutting them from the tree and throw them out with the trash.
Q: What are the black spots that are all over my rose bushes?
A: This is a disease called black spot. It is a common and disfiguring disease of roses. Fungicides are more effective when applied as a preventative disease control. We suggest alternating between different fungicides to reduce any chance of disease resistance. Roses will need to be sprayed once every 2-3 weeks from May through September to keep black spot and possibly other problems under control. See our staff for guidance and specific control recommendations.
Q: What is eating holes in the leaves of my hosta?
A: Slugs are the most likely culprits for chewing holes in hosta leaves. Slugs are most active during wet, cloudy weather in late spring and early summer. Slug baits offer easy and effective control of this pest. Sluggo is the most popular bait because it is approved for use around pets and children. Always follow the label directions.
Q: Ants are everywhere in my garden, how do I get rid of them?
A: Ants are beneficial insects. They are scavengers and predators and do not injure plants. They may become a nuisance by building mounds in the garden or entering into the house. Ant mounds can be treated with a drench of permethrin. If ants are becoming a nuisance entering the house, try placing a 2'-4' wide band of granular permethrin around the perimeter of your home. Always read the label directions before using.
Q: What can I do about Japanese Beetles?
A: Japanese beetles can be difficult to control, combining different strategies will give you the best results. They spend most of their life in the soil as a grub feeding on plant roots. Treating the soil with Milky Spore is a long lasting, natural control for the grubs. Adult beetles may continue to be a problem in July and August and will require periodic spraying with insecticides to keep them under control. Ask one of our plant specialists for recommendations on which insecticide should be used.
Q: Help, these mosquitoes are driving me crazy!
A: There is now easy answer for this one. Combining a variety of control strategies will be the most effective approach. First, eliminate a sources of standing water such a puddles, clogged gutters, etc. If you have birdbaths, or standing water, which cannot be eliminated, add Mosquito Bits to the water. This is a natural product that will not harm pets, people or wildlife. It is a bacterium that infects only the mosquito larvae. Protective clothing and insect repellents can also be effective in preventing mosquito bites. Also consider creating a habitat for birds and bats, natural predators of mosquitoes. Spraying the area with insecticides will offer temporary relief at best and should be used with descretion. See our staff for guidance.
Q: What about ticks?
A: Ticks are treated much the same as mosquitoes, however we have fewer control options. Ticks live in tall grass, weeds and wooded areas. Keeping weedy vegetation under control can help to eliminate habitat. Protective clothing and repellents are the most effective approach for preventing tick bites. Spraying the area with insecticides will offer temporary relief and should be used with descretion. See our staff for guidance.
Houseplants
Q: Why are the leaves on my ficus tree turning yellow and dropping off?
A: Leaves turning yellow and dropping off is how a plant responds to stress. The stress can be caused by being too wet, too dry, too hot, etc. If you contact one of our plant specialists, we can discuss your situation with you and determine what might be happening. Ficus plants will frequently react to the stress of being moved from one location to another and will drop leaves for the initial 2-4 weeks as they become acclimated to their new environment.
Q: What is the sticky substance on the leaves of my houseplants?
A: The stick substance is honeydew, a substance secreted by sucking insects. The most common cause for this in houseplants is brown scale. Brown scale is difficult to see, and they do not look like insects you are familiar with. Brown scale attach to the leaves and twigs of plants and look like bumps on the plant. You can apply horticultural oil and other products to control the scale. See a member of our staff for specific product recommendations.
Q: When is the time to bring my hibiscus and other tropical plants indoors for the season?
A: Tropical plants should be brought indoors when nighttime temperatures are going below 50 degrees Fahrenheit. Consider spraying the plants with an insecticide such as horticultural oil, or permethrin to prevent bringing any insects in with the plants. See our staff for specific product recommendations. Always follow the label instructions.
Q: In general, when should houseplants be re-potted to allow room for adequate root growth?
A: If your plants slow down in their growth rate, the soil seems to be drying out rapidly, or you see roots coming through the bottom of the container, it is time to repot your plant. When it is time to repot, select a container just slightly larger than the one it is currently in and check to see that it has drainage holes. Loosen up the roots of the plant, place it in the new container at the same depth as before and add additional potting media such as Merrifield Potting Mix. Water thoroughly to settle out any air spaces.
Q: Do I need holes in the bottom of my pots for drainage?
A: Yes, good drainage is essential for healthy plant growth. Pots that do not have drainage holes are best used as decorative containers. You can place a container that has drainage within the decorative pot if you like.