Growing Concerns 598: Boston fern indoors, dog urine

Early Winter! 

Humidity and light keep a Boston fern in fine fettle


Dear Janet,

Any tips on overwintering Boston Ferns indoors? I trimmed their dead leaves and gave them a shower yesterday. They look pretty happy now. How often should I water them? When they were outdoors, I watered them everyday. Should I fertilize at all?


 Dear D.R.,

Give them the best light and humidity you can. The best place for them may be in a bathroom with a south or east facing window. Keep them away from heater vents. Even so, it's unlikely they'll be receiving as much light or humidity as they would get outdoors or in a greenhouse. They'll have to skinny down by losing some leaves. Expect more shedding, and the need for more grooming sessions.

Standard rules for watering interior plants apply to Boston ferns. How much water they need is determined by the size of the pot and number of leaves there are to take up water.

Put water into a measured container and pour it slowly over the soil surface until it begins to seep out of the drainage holes. Let water sit in the catch tray for just twenty minutes, while light is on the plant, to see if more water is taken up into the foliage. Then pour off the excess. Note how much you used and how much you poured off. Each time you water, apply that same amount

How frequently the plants need water is directly dependent on how much light they get. The better the level and duration of light, the more water they'll use. Unlike some plants that need periods of warmth and drought, Boston ferns like steady moisture on their roots, so don't let the soil dry down between waterings. Water whenever the soil surface begins to feel warm and dry, or the pot loses water weight.

Don't fertilize in winter unless you have the plants under grow-lights.


 Dear Janet,

I planted an arborvitae hedge two years ago. Recently, I noticed some of the bushes had brown spots on the bottom about 12 by 12 inches. I believe these are from dog urine. I think the dog is cooperating now but what can be done about the brown spots? The bushes are very healthy otherwise. Also, what fertilizer do you recommend and how often should I apply it next year?


 Dear R.C.,

Dog urine burns foliage. Needles and twigs in those spots are probably dead, but the plant can eventually fill those spots with new growth from branches nearby. This coming March, cut out the brown. That will allow light to reach into the gap to stimulate adjacent buds. You can even bend and tie in a few flexible limbs, to speed the process.

What kind of fertilizer you use isn't tied so much to the plant as to the soil. If a soil test through shows that an area is deficient in phosphorus or potassium, you'll use a formulation that compensates for that.  High phosphorus- and high potassium fertilizers have relatively high second or third numbers -- 5-10-5 or 6-24-24, for instance.

However, don't use such fertilizers unless you have a soil test that indicates a deficiency. Instead, use a balanced fertilizer such as 10-10-10 or 2-2-2. If it's a fertilizer that indicates it is slow release, or formulated with micronutrients for acid loving plants, all the better in your alkaline soils.

No matter which fertilizer you use, apply it so it can be taken up by the plant while it is in most active growth. Spread slow release formulations such as Osmocote or Driconure in late winter or early spring. They will then be dissolving or breaking down throughout the April to June flush of growth. Spread water soluble products, granular or powdered, two or three times at intervals from mid-April to early June.

Whatever you use, scratch it into the top few inches of soil or make sure it's covered by moist mulch so that it will melt or decompose.

Apply enough so that every hundred square feet of soil surface over the root zone receives about two-tenths pound of nitrogen during the shrubs' growth period. The nitrogen content of a fertilizer is given in the first number on the three-part formula. A 10-10-10 contains 10 per cent nitrogen, and two pounds of that product supplies the needed two-tenths of a pound of nitrogen. A 2-2-2 has two per cent nitrogen, so you need ten pounds for each 100 square feet of ground.


Green thumbs up

to evaluating a landscape now. What looks good in December is probably a keeper. What looks bad now will compromise that scene's appearance for three months. Does that plant's spring bloom or summer luster really compensate for this long spate of ugliness? If not, start looking now for spring and summer bloomers that also carry their weight in winter.


Green thumbs down

to that feline compunction that causes a cat to begin each houseplant-eating episode with an attack on an undamaged leaf. I could grant a cat one leaf at a time, to be chewed off in stages over a week or so. What riles me is that wasteful progression to the point where every leaf is just a little bit tattered.

Originally published 12/25/04