Q: What can you tell me about the tiny yellow flowers that I'm seeing this year? They're low-growing and smell so nice. I see them along the streets, and they seem to have taken over undeveloped lots and grass along sidewalks. I suppose they're weeds, but what fragrant little weeds. - Patricia Belknap, Fargo.

A: The low-growing fresh green mats of foliage covered with golden yellow flowers are birdsfoot trefoil, widely seen along street boulevards in newer developments and along roadways. A closer look shows clover-like foliage and pea-like flowers typical of members of the legume family.

Birdsfoot trefoil is a good example of a weed's definition: any plant out of place. Agriculturally, it's seeded in livestock pastures as a forage crop, and there are even named cultivars. Because it's a legitimate, valuable crop, it's only a weed if it's in an unwanted place, such as the unintended overtaking of a home lawn.

The Minnesota Department of Natural Resources has declared it an invasive species because its dense mats can choke out other vegetation as it spreads by seed and underground rhizomes. It's a perennial plant, winter-hardy in our region.

Birdsfoot trefoil thrives under dry conditions, allowing it to spread easily in lawngrass that is stressed by drought. Whether or not to use lawn weed herbicides to control it depends on your viewpoint.

Q: Our Summer Wine ninebark shrubs around our patio are developing an increasing number of white leaves on them. Can you tell us what might be happening and is there anything we should be doing about it? - Loren and Jennifer Lien, West Fargo.

A: Summer Wine ninebark and other purple-colored ninebark shrubs are susceptible to a common fungus called powdery mildew, which appears as a grayish-white coating on leaves. It can begin as small spots on a few leaves and progress until gray leaves cover most of the shrub.

Powdery mildew doesn't usually affect the long-term health of shrubs and perennials, but they become less attractive. However, it's certainly best for the shrub if it's controlled.

Once leaves are infected, the powdery coating usually won't disappear. Application of an all-purpose fungicides labeled for powdery mildew control on shrubs and perennials sprayed over the foliage can prevent the spread to healthy foliage. Avoid wetting the foliage with overhead sprinkling, which greatly increases the disease's spread.

Q: Leaves on a tomato plant are curling inward yet there's no sign of bugs, blight and no herbicide spray. The plant is dark green and has fruit. What's the cause? - Carol Rethemeier, Perham, Minn.

A: It's the disorder called physiological leaf roll. It's not a disease, but is caused by environmental interactions including excess moisture, insufficient moisture, heat and root damage.

The good news is that according to Clemson University it doesn't affect the overall production of tomato fruits. The rolled-up leaves often first appear when early summer transitions to mid-summer. It's more common on indeterminate (vining) varieties than determinate (bush) types.

Once leaves roll, they usually don't unroll. Mulching the soil before the disorder occurs might help and is generally a good tomato-growing practice.

If you have a gardening or lawn care question, email Don Kinzler at ForumGrowingTogether@hotmail.com. All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.