Spring planting tips from a gardening meteorologist

Since we last spoke two weeks ago, we have been below freezing and well up into the 80s... Yep, it is springtime in D.C.! I mentioned a time or two that getting down a bed of mulch right now sure helps to even out those temperature extremes and protect all those wonderful plants now just coming to life

I did want to make a pitch that in addition to the mulch this year, think about putting down some compost prior to the mulch. Compost (basically decayed vegetable matter) is a great source of nutrients for your flower and vegetable beds. As unprocessed health food is to us, compost is to plants. Not only that, but it also helps to lighten up those dense clay soils that many of us here on the East Coast fight every year. You can get the gardening gold at most large nurseries in the area, either in bag or bulk. I put some down every year and the soil just gets more and more amenable to all my plantings.

Current average temperatures where are a good approximation for soil temperatures. (High Plains Regional Climate Center)

In addition to waiting for the right temperature to plant, you should also hold off planting until threat of frost has passed. So when is that? Well, it does vary across the area.

One website I like that gives frost dates by probability of occurrence is Davesgarden.com. Just enter your zip code and it lists a few representative sites. For me in downtown D.C., the average last freeze date is April 15 but if I want to plant something that I absolutely do not want to take a chance of frost with it shows that the 10% probability of a frost is May 4.

From a moisture standpoint, we are in a really good spot right now. With recent rains (over the last couple of weeks) running only 50 to 75% of normal, the topsoil has dried enough to be easily workable. And due to the abundant rains earlier in March, our subsoil moisture is favorable so plants will have water to root down to.

The rain outlook for the next two weeks promises about a half to three-quarters of an inch in the next 5 days and then a good week of drier weather leaving us a nice window to work the soil. Avoid tilling for at least three days after a normal rain.

Looking at all those beautiful beds of daffodils and now some of the early tulips is such a treat. I recommend planting annuals or later perennials in these beds. They will help to cover the floppy foliage after the bloom is over. That way we won’t be tempted to the torture of bound daffodil leaves later :)

I would like to make an impassioned appeal as our lawns start to green up and the plantings go infor restraint when it comes to fertilizer. I love a lush green lawn as much as the next person but recent studies have contended that we may be responsible for a significant part of the runoff fertilizer that challenges our beloved Chesapeake Bay. If you do it yourself, please be conservative in your applications. And if you use a service, try to ensure that they are environmentally aware.

As for the flower beds, there are many good slow release fertilizers on the market now that help to limit runoff. The added benefit is with most of them you only need to apply it every four months allowing more time for weeding! Yes, the dandelions are already in full bloom and we will talk a little about them and other fun spring time topics in two weeks. Happy gardening!

Capital Weather Gang meteorologist David Streit is also an active gardener. He earned a certificate in landscape design from the USDA Graduate School and volunteered many years at the National Arboretum.