This article was published originally on 4/28/2010
In just a few short weeks we will pass the frost-free date, May 10th, for most of Iowa. Then, gardeners will finally be able to plant warm season vegetables. In the mean time, your cool season crops can use maintenance.
The acclimation process can begin now for warm season crops that were started as seed indoors. On nice days put the starts outdoors in a protected area for a few hours at a time then bring them back in before evening. Avoid direct sun until the tender starts have acclimated to the relatively more extreme conditions present outdoors. Plants that are 'hardened off' early can withstand transplanting and other stresses more effectively.
Remember that it is good practice to rotate your vegetable garden every year. For example, if tomatoes or their close relatives in the Solanaceae family are grown in the same location for too long, they tend to build up disease and insect populations. At least a two or three year rotation with other crops will prevent these harmful buildups because pests are typically specific to either one or a few species within a plant family. However, exceptions apply for certain generalist pests.
The benefit of diversity in rotation is only one reason to branch out to cool season vegetables - they can also tolerate light frosts. Some examples of cool season vegetables, which can be planted up to four weeks before the frost-free date, are broccoli, cabbage, lettuce, onions, peas, potato, radish, rutabaga, spinach and turnip. For those cool season crops, it might be time to thin the direct seeded varieties. Most gardeners tend to plant species with small seed at high rates. In the image below, the rows of radishes, spinach and rutabaga need to be thinned. Vegetables that are planted too densely do not yield well.
Now is the time to incorporate compost into your garden as well. Prepare the planting bed for warm season crops by incorporating compost during tilling. Additionally, compost can be top dressed in cool season vegetable beds.
Early spring garden. Photo by Jenifer Bousselot.