When is the best time to start seeds indoors

  • Article by: Nancy Rose
  • Contributing Writer
  • March 6, 2002 - 10:00 PM

QWhat vegetable and flower seeds can I sow indoors and when should I start?

ASome flowers and vegetables grow rapidly from seeds while others take much longer. Ideally, the seeds should be sown early enough to produce sturdy transplants by the time outdoor weather conditions are right, but not so early that plants become lanky and pot-bound.

Proper planting time varies depending on whether the plants can tolerate colder air and soil temperatures (pansies, snapdragons, broccoli and cabbage are examples), or whether they must have completely frost-free conditions before planting (impatiens, tomatoes, peppers).

So how to divine the precise moment for sowing seeds? Many seed packets and seed catalogs provide information on when to start particular varieties. The timing is usually put in terms of "sow seeds X number of weeks before planting time."

Late February is still too early for sowing fast-growing plants, such as tomatoes and marigolds, which only require about four to six weeks before planting outside in late May. But many vegetables and flowers can be started now. Onions and leeks can be started in February, and parsley, both curled and flat leaf, is somewhat slow to germinate and can be started now.

Numerous annual flowers that require 10 to 12 weeks of lead time should be planted in February as well. These include annual geraniums, impatiens and petunias. Other flowers that can be started within the next few weeks include snapdragons, lobelia, statice, vinca (Cathyranthus) and stocks.

All of your work will be for naught if you plant your seedlings outdoors without first hardening them off, a process of acclimating the tender, succulent indoor-grown seedlings to the much harsher conditions outdoors. Temperature changes are greater, winds are stronger and the sun is much brighter outside, so the seedlings must gradually be introduced to these conditions.

On warm days (usually by early May), the flats of seedlings can be put outside in a shaded, wind-protected spot for a few hours. Bring plants back inside at night when starting the hardening-off process. Frost-sensitive plants must be protected when freezing temperatures are predicted, even if the plants are nearly fully hardened off.

Increase the length of time plants are outside each day and gradually move them into more sun. Plan on one or two weeks of hardening off, depending on weather conditions.

QI want to choose a lawn care product that's best for my family, pets, and the environment, but I'm confused about the content of these products. I bought a bag of phosphorus-free 25-0-10 "weed and feed," but was dismayed to read all the warnings about not letting children or pets on it and requirements to wear gloves, long pants, etc. when applying it. Then I read about an environmentally responsible 8-1-1 weed and feed product with corn gluten as the active ingredient. My questions are 1) what do the numbers 25-0-10 and 8-1-1 refer to?, 2) is it true that some phosphorus is necessary, and too much nitrogen is not good?, and 3) is it the polymer coated urea and/or the regular urea in the 25-0-10 product that results in all the warnings on this product?

AThe numbers 25-0-10 and 8-1-1 refer to the amounts of nitrogen, phosphorus (in the form of phosphate) and potassium (in the form of potash) present in the fertilizer. These three nutrients, often abbreviated as N, P, and K, respectively, are essential for plant growth. Fertilizers are available in many different formulations, or grades, and these grades must be clearly marked on the package. The numbers 25-0-10 mean that there is 25 percent nitrogen, no phosphorus, and 10 percent potassium. The 8-1-1 has 8 percent nitrogen, 1 percent phosphorus, and 1 percent potassium.

Too much of this is bad

Phosphorus is an essential nutrient required for plant growth. However, most soils in this region already have adequate amounts of phosphorus present in them. When excess amounts of phosphorus enter waterways it can pollute streams and lakes and cause overgrowth of algae. Runoff from lawns treated with high-phosphorus fertilizers seemed a likely culprit in this pollution, but studies have shown that carefully applied phosphorus fertilizers are not a major source of phosphate pollution. For any fertilizer, with or without phosphorus, it's very important to avoid spreading it on driveways, sidewalks, or gutters where it can be washed into storm sewers and then into waterways. Also make sure to gently water all fertilized areas after treatment so that the fertilizer moves into the soil. Once phosphorus is in the soil it moves slowly and is unlikely to leach out. A much larger source of phosphorus pollution is eroding soil and plant material, such as grass clippings and fallen leaves, that are washed into storm sewers. You can help prevent lake pollution by keeping fertilizers and vegetative yard waste out of streets and sewers.

Nitrogen is also an essential nutrient. It moves rapidly through soils and is the nutrient most likely to need replenishing on a yearly basis. Applying fertilizers with high nitrogen contents can result in sudden lush growth in turf grass. Unless it is formulated to release more slowly, nitrogen causes a quick growth response but then the grass may decline as the nitrogen is depleted.

This leads to the third question. Urea is a form of nitrogen which is commonly used in fertilizers. 'Regular' urea will give the quick burst of growth I just mentioned. This can be useful for giving vegetable crops or annual flowers a quick boost in early summer, but for turf grasses a more even release of nitrogen will result in steady, moderate growth. That's what the 'polymer coated' urea helps with. The coating on the urea nitrogen makes this a slow-release fertilizer. Slow release fertilizers are also useful for perennials, plants in outdoor containers, and for houseplants.

Wearing gloves is recom


It's a good basic safety precaution to wear gloves and suitable clothing when applying any lawn product. Urea fertilizer has some potential hazards, such as getting stuck in a pet's paws where it could cause skin irritation, but the main cause of the warnings was probably the 'weed' part of the 'weed and feed'. These products combine herbicides such as 2,4-D with fertilizers, and herbicides must always be used with caution. Follow label directions carefully, don't over-apply, and make sure the product is thoroughly watered into the lawn.

While corn gluten meal is a less dangerous product than herbicides such as 2,4-D, it is not effective at killing existing weeds like dandelions. It is a pre-emergent herbicide, which means it prevents weed seeds such as crabgrass from germinating. The weed preventative effects of corn gluten meal may improve after two or more years of use on the lawn.

Follow label directions carefully, don't over-apply, and make sure the product does not contact non-target plants such as perennials, shrubs, and ground covers.

-- Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.

© 2018 Star Tribune