Most gardeners across the country generally buy and plant out annual bedding plants on a certain magical date. It's the one that, over time, has been deemed the safest for planting because the chance of frost and extremely cold temperatures is much decreased by this point in the season. In my USDA Zone 5 garden, Memorial Day weekend is the traditional target.
But many ornamental annuals, as well as some vegetables and herbs, actually benefit from being planted out earlier and will consistently grow better under cool, moist conditions. (For me, late April to early May.) Even petunias would fare far better if they were planted out long before their first buds begin to open. Gardeners who save their planting for later dates are missing a unique opportunity to get their plants in the ground when the conditions for growth are ideal. And despite common wisdom, not all | annuals will be harmed by the light frosts to which planting out early may subject them.
The Memorial Day formula I was brought up on is based on the common assumption that annuals are a universal group of similar plants, with identical needs. In fact, they are just as complex a group as perennials, with varying requirements of soil, temperature, water, and light. The plants we grow today as annuals originate in all the u corners of the world, and their needs have a great deal to do with their place of origin.
THE KEY TO SURVIVAL
Critical to the survival of any plant set out in spring is the period when plants are gradually transitioned from a sheltered growing space to harsher outdoor conditions–usually referred to as hardening off. But these days, even hardy perennials are commonly grown inside greenhouses and then offered directly for sale. If the nursery where you bought them can't guarantee that your plants have already been hardened off, you can do it yourself. Over three or four days, put the plants outside during the day, then bring them into a sheltered spot at night. Their cell walls will adapt quickly to weather conditions. In fact, exposing a plant to direct sunlight and windy, cooler conditions than those to which it is accustomed will result in changes that you can actually feel in the plants physical texture if you run your hand across the top of it. After a few days of hardening off, transplants will be prepared to survive chilly nights in the garden. Of course, if temperatures are predicted to dip really low (into the middle 20os F) you may want to throw a blanket over them that night.
Some nurseries and garden centers offer a limited selection of cold-hardy annuals, but more often than not, they offer them only later in the season. So, to plant annuals outside in April or early May, when the weather is best for their establishment, you may have to grow them yourself. Starting your own seeds is a good way to greatly increase the selection of plants you can grow. From my own experience, the key points to remember when starting seeds are to use a well-drained soil mix and to avoid over-watering. Provide your seedlings with adequate air circulation and as much light as possible. Full sunlight (or the equivalent from an artificial source) is essential for the growth of quality transplants.
Once they've grown to a sturdy size, try to time the plants' move outdoors so that it coincides with a stretch of cooler, overcast or even rainy days. Ideally, they should have three to four days of hardening off to adjust to outdoor conditions, and then move permanently outside in weather that will not unduly stress them. After they are planted, if there is no appreciable rainfall, water your transplants by soaking them thoroughly every three to four days for the first week or so. By the second week, their roots should extend beyond where they were in the cell packs, ready to search for moisture and nutrients from the garden at large.
Not all plants are cut out for transplanting. Some have roots that resent disturbance, and despite the gardener's best efforts, they will not recover well from the shock of a move.
Instead, these will grow best seeded direcdy into the soil, in the garden location where you want them to remain. Corn cockle (Agrostemma spp.), throw-wax (Bupleurum spp.), larkspur (Consolida spp.), hounds tongue (Cynoglossum spp.), and annual poppies (Papaver spp.) are among the annuals that perform best from direct seeding. The great thing about fhese plants is that once established, they will generally self-sow, requiring only a quick thinning in future seasons.
The best time to direct sow is from late summer to early winter. The seeds will lie dormant until the spring. If you grow them in groups, your seedlings will look distinct from weed seedlings. Survivors should be judiciously thinned, or the seedlings will be far too crowded to reach maturity in your garden. After thinning, they will require surprisingly little care, as long as you keep an eye on early spring conditions.
When you have especially enjoyed any plant, you should consider saving its seed. It's a relatively straightforward process; the trickiest part is figuring out when the seed has ripened. Generally speaking, when you cannot penetrate a seed with your fingernail, it has sufficiently ripened to harvest. Once the seed has been harvested, it should be left to air dry for several weeks before it is placed in an airtight package and clearly labeled. After that, storage in a home refrigerator is ideal. Seeds stored in this fashion will generally keep for several years, although their viability is best in the first season. Remember that in the case of annuals that are best sown directly, planting the seeds later that same year may be preferable to storing them until the following spring. H