How to maximize dahlia blooms and keep grass green
In the Chicago area so far this year, there has been adequate rain to keep bluegrass lawns green and growing, and my home lawn is still looking healthy.
Established bluegrass lawns need about an inch of water each week to continue to actively grow and stay green throughout the summer. Water deeply once a week — no more than twice a week — rather than lightly multiple times a week. This promotes a deeper root system so the grass will hold up better to stress.
I do not ever water my lawn at home and always appreciate it when it goes dormant and only needs to mowed once every couple of weeks or so.
To determine how long it takes your sprinkler to deliver one inch of water, set out a coffee, tuna or other shallow can with straight sides and time how long it takes to fill it with an inch of water.
Be consistent with your watering practices — either water regularly all summer, or let your grass go dormant during hot, dry periods. If your soil is heavy clay and long periods of watering cause water to run off, you may need to split watering into a couple of times per week. Mowing your lawn at a height of three inches or more will also help the grass withstand stress and keep out weeds.
Banishing blackspot
If your hybrid roses are losing their lower leaves and remaining leaves have yellowish foliage with dark spots, you may have a common fungal disease called blackspot. Begin a spray program with approved fungicides immediately. The fungicides must be applied once every seven to 10 days as they work to prevent the disease.
These fungicides do not cure what is already infected. Be sure to clean up any leaves that have fallen from the plants.
Many landscape shrub roses are resistant to black spot disease, so they do not need to be on a spray program.
Maximizing dahlia flowers
If you want to maximize the size of your dahlia flowers, keep the main stems free of side shoots. This allows only the terminal bud to develop, which results in one flower per stem. This method is most effective for the large, dinner-plate-sized cultivars. The plants may need some support to prevent wind damage and to keep stems from breaking from the weight of the flowers.
Dahlias growing in pots in garden centers are usually bedding types that do not produce large flowers. These do not need staking.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.