This is a tricky situation. Looking over your past questions has helped us understand your planting areas. You may want to check with your county about the critical area buffer zone and using herbicides. From past photos though, it looks like you are far enough from the edge of the water to safely and successfully use herbicides. 

To help manage the crabgrass, you may need to use a pre-emergent and hand weed (if you don't want to use a liquid systemic herbicide) and wait a few weeks to plant. Typically after applying the pre-emergent it will take 4-6 weeks (it will say on the label directions) before you can seed anything else. Perhaps you could plant the poppies and other annuals in plug or seedling containers and transplant after they are big enough. 

Another thought if you are constantly struggling with weed management, is to incorporate thicker plantings of perennials, and perennial ground covers to help cover bare areas in the garden beds. You could still add in some visual interest with annuals in pockets throughout the garden. Using 'green' or living mulch is a good way to help cut down on weed seed germination in the garden. 

We would not recommend using corn gluten for a preemergent organic alternative since it will make the nitrogen content too high which could wash down into the water. When looking at the labels or searching for a product, you may want to make sure you can find one that is aquatic safe. 

In Calvert county you can apply crabgrass pre-emergent probably around mid- March. You just need to watch the soil temperatures since if you apply it too early it will not be able to activate and if it is too late the seed will start to germinate. This is explained on the link above for pre-emergent. 

If you have further questions on timing or how to apply, please let us know. 

Emily 

There is no easy way to successfully prevent crabgrass from germinating while still being able to direct sow your annual seeds. To get the crabgrass under control you may need to only plant transplanted annuals that you start in containers for this year. The preemergent needs to go down just BEFORE the soil temperature is consistently 55 degrees for multiple days so this could be done around mid-March. You would have to wait to direct sow annual seeds about 4-6 weeks depending on what the label says for the seeds to be able to grow and not be effected by the chemicals. A second application if needed can be applied but you would need to refer to the product label on timing since it could be different for different chemicals. 

A lot of people who plant annual seeds have success with winter sowing in milk jugs and various containers to obtain the cold stratification necessary for many of those flowers. The link is to a blog post which will explain how you can start this.  There are also groups you can join on social media platforms to learn more and they can be really helpful with sharing different techniques of what has been successful for them. 

We don't have a specific product we can recommend for a preemergent but you can explore the different chemicals listed on our Preemergent site to see which is best suited for your needs. 

Just to caution you though, we wouldn't recommend using a product called PREEN with the active chemical of trifluralin since it is harmful to marine and aquatic life. The label explains that it should not be used where it could potentially runoff into a water source. 

Emily