MaryAnne Spinner, Chicago Master Gardener

The calendar says it's Spring, and the daffodils and crocus are blooming. The woodies are budding out, and everywhere you look, little green and burgundy sprouts are popping up from under the mulch. Garden centers have stocked their shelves with pansies, violas, primroses, and ranunculus, and we are just so ready to rock and roll.

Time to go shopping and plant up those window boxes, right? Well, not so fast. How long have you lived in Chicago? If your long-term memory bank hasn't emptied yet, you will recall many an April when the temperatures fluctuated wildly, when frosts came upon us willy-nilly, and when we awoke to find snow covering the tulips.

If you sell them, they will come...

The problem, like the apple in that first garden of Eden, is temptation. All those frilly flowers call to us from the shelves of the local nursery, and a still-bleak landscape just begs to be jazzed up. Beware the tender trap!

Case in point: A couple of years ago, dear friends moved here from Texas. They had just survived the brunt of their first Midwestern winter, which was coming to an end with a gorgeously mysterious spell in the 70's, while the calendar still only pointed to the second week of March. That weekend, I happened by their house and noted two huge urns flanking the door, stuffed with fully leafed-out caladiums, speckled red and pink and looking very perky. I was aghast at the sight–didn't they know? I rang the doorbell and enquired delicately as to why they had put caladiums outside to suffer in Chicago's March. Well, they replied, we always put out caladiums in Texas this time of year. And, don't y'all know, the garden center was selling them. Didn't that mean it was time to put them outside?

Don't fall for it

Yes, you can buy ranunculus in March, and maybe they'll survive. But if that frost hits, you'll remember bitterly not only the cost of the demised plants, but also the painful hour you spent planting, fingers freezing inside the flimsy green gardening gloves, nose running, only to find raggedy ex-flowers on brittle stems two days later. Better to wait until at least mid-April, when your investment is safer and the selection is better, too. Garden centers will put plants out at the time most convenient for their shipping contracts and inventory needs, and that does not guarantee survival. Next time there is a cold snap, in fact, drive by your local center, and you'll see that they will have covered their outdoor displays with tarps or brown paper.

Even the most honest and reliable garden centers are guilty of this little white marketing lie, just as they sell hydrangeas and kalmia that are only marginally hardy in our zone. Plus, they know how crazed we gardeners can be, and how to take advantage of our fear that if we don't buy those unusual begonias today, they may not be there next week and we will never, ever see them again, oh no! What separates the ethical nurseries from the shoddy, I have found, is their willingness to tell you the truth, if you know enough to ask.

The good, the bad, and the frozen

Once April is here in earnest, you can buy a number of plants that will tolerate cool weather. Besides the afore-mentioned pansies, violas, primroses, and ranunculus, try annual flowers such as snapdragons, sweet peas, bacopa, nasturtiums, zinnias, calendula, and sweet alyssum. Certain vegetable crops actually should be planted at this time, including peas, carrots, radishes, beets, lettuces, spinach, cool-weather greens such as chard and kale, and the various hardier Asian greens like mustard and mizuna.

However, tomato, eggplants, and peppers belong inside this time of year, under lights. Don't even think about setting them out in your garden, whether or not Garden Depot sells them. The cucurbits–cucumbers, melons, pumpkins, and squash–also demand warmth, and should not be planted out until the soil is truly warm and the weather is settled. In our Zone 5 climate, I typically wait until Memorial Day weekend to plant tomatoes and peppers, and another week or two before planting cucurbits and eggplants.

Other planting pitfalls

Plant purchase missteps don't just occur in the earliest part of the garden season. Later on after the last frost (generally around mid-May here), you will find that garden centers are filling up with tropicals. Resist the temptation to buy these until June, as most tropicals–colocasias, alocasias, cannas, and the like–prefer warm soil. Even if the air temperature is balmy, the soil in your garden may not have warmed up sufficiently to support proper growth. Soil temperature should be at least 50 degrees Fahrenheit, but even then, growth will be slow; aim for 60 degrees at a minimum. Another popular foliage plant that absolutely must have warm temperatures is coleus. Without warmth, both in the air and soil, your coleus may just keel over and collapse.

A number of herbs can be grown successfully in early spring, such as parsley, lovage, borage, chives, and sweet cicely. But basil is a wimp and absolutely detests cold weather, and rosemary is most definitely a sun-worshipper. Use geography as a proximate rule of thumb: if you're considering herbs that grow abundantly in Italy or the south of France or Viet Nam (or if you're not big on geography but like to cook and know that they are commonly used in those countries' cuisines), then the herbs in question won't like Chicago in April. But if the herbs grow well and are much-loved in England or Germany or Korea, then you're probably ready to plant.

If you've been growing annuals or veggies from seed indoors under lights, remember to harden them off properly when you move them outdoors. Plants grown inside under perfect conditions will be highly sensitive to extremes of both cold and heat, and especially to desiccating winds. About ten days before you're ready to plant, take them outside and put them in a sheltered spot away from bright sunshine and wind for an hour or two, then bring them back indoors. Continue doing this for the next several days, increasing the time spend outdoors by a couple of hours each day. Then they will be ready for transplanting. Even then, check your transplants carefully for the next few days, and cover them with an overturned pot or bag if it's too sunny or windy.

Make sure you keep young plants well-watered after planting out; when plants are not yet established, their roots cannot take up all the water that they need. This is especially important if you have planted up containers and hanging baskets, which dry out quickly. At the other extreme, watch your plants carefully if there is a great deal of rain (such as our typical April thunderstorms). Without extensive root systems to anchor them, young seedlings can be uprooted from their containers and washed away. You can tuck them back into their pots if you're vigilant, but if you let a day pass, they may dry fatally out.

Strategies for beating the weather

There are a number of gizmos on the market that allegedly help extend the growing season, both at the front and back ends. These include hot caps, glass cloches, floating row covers, and plastic gadgets that look like upside-down umbrellas, as well as all manner of cold frames. While I have not tried many of these products, my understanding is that they will allow you to plant tomatoes a couple of weeks earlier than normal; only you can decide if it's worth the effort and cost. In my experience, a couple of Marshall Fields shopping bags upended over my plants works just fine when frost threatens (although after this year I will refuse, as a loyal Chicago native, to use any Macy's bags).

One device I do swear by is a relatively inexpensive, lightweight portable greenhouse. Constructed of green metal poles and four grid shelves, it is protected by a clear heavyweight plastic covering with a zippered door. At a very manageable size (about as tall and wide as a small refrigerator, but weighing only a few pounds), these greenhouses can go in the garden or up on the deck when needed, then break down and fold flat for storage in the basement over the winter. The most ingenious part of their construction is the door: by day, unzip the door and roll it up so that the plants get warmth and air, and then at night zip it back up again, so that the trapped air keeps the plants warm through the night. I have found that this makes the perfect substitute for the heavy lifting and constant ferrying of plants during the hardening off process; I can put all my tender plants in the greenhouses, and then unzip the door for the requisite amount of time each day. Several mail order companies such as Burpee carry this item at widely varying prices. The best price I saw recently was $65 at Smith and Hawken (www.smithandhawken.com).

Another practical and relatively inexpensive way to extend the season is by "solarizing" the soil in your garden beds: cover the soil with heavy black plastic, weighted down with bricks or rocks, for four to six weeks before planting your veggies or annual flowers. The solarizing process will warm the soil and make your garden beds more hospitable to your plants, but remember that the soil must be moist before covering it, and the plastic heavy enough to keep in heat. Note that there are important ancillary advantages to the process. Not only does the soil warm more quickly, but solarizing destroys some common soil-borne diseases (such as tomato viruses), and also kills many weed seeds, so you will have less weeding to do later. Just remember not to cultivate too deeply after removing the plastic and planting, or you will bring buried weed seeds up to the top and back into the sun's warmth.

When all else fails

Now that I have described some best practices, it's time to 'fess up. Just last week, seduced by the jewel-like intensity of ruby, amethyst, and sapphire petals glowing in little green plastic pots, I purchased several small primroses for the old concrete fountain-turned-planter in my backyard. Yes, yes, I know it was the first week of April and the temperatures were borderline, but I needed to have something growing out there after the long winter...and I don't know if I'll find primroses anywhere next month, and I've just got to have them. Now every day, when I boot up my computer, my first task is to check the forecast at www.weather.com, and pray.

Do you have a gardening question? Email the Extension's Electronic Plant Clinic at rwolford@uiuc.edu, and our Master Gardeners will be glad to assist you.